1998 January 1

Painting Railway Equipment:

By ERIC WILDE

This article covers the steps that should betaken to prepare railway equipment for painting(both interior and exterior), the application ofpaint, the types of paints that are available andcan be used to paint railway equipment and thetools that are used to apply the various coatings.

The painting of railway equipment is apractice that is as old as the business ofmanufacturing railway equipment itself.Consequently, the profession of car painter is anold and honorable one. However, over thedecades, as the profession has gained itsvenerable status, many things have changed. Thecoatings industry, under pressure forenvironmental concerns, has developed paintsand finishes that were undreamed of when mostof our cars were built.

Along with the advances made in coatingscame many commensurate advances inapplication equipment, some of them as a directresult of the need to apply the new coatings. Theadvances have been so great in many ways that agood paintbrush, far from being all that isnecessary to get into the painting business, isnow just the tip of the iceberg as far as paintingequipment is concerned.

Although we are restoring old railwayequipment, there is no reason why the coatingsand finishes that we use shouldn’t be state of theart. In fact, some of the old paints that wereoriginally used aren’t even available now so wemust switch to the latest types.

This article will detail all of the stepsnecessary to prepare and paint railway equipmentboth inside and out. It will cover the all-important area of surface preparation with specialemphasis on the materials encountered in arailway car. The types of coatings and finishescommonly used to paint railway equipment willbe examined along with their properties andmethods of application. As the story unfolds, themodern tools and equipment employed by thepros to achieve the beautiful and durable finishesthat one sees today will be covered.

It should be noted in passing that there are aplethora of products designed for the automotiveindustry along with volumes of referencematerial on how to use it. Anyone who is settingout to paint their railway car is advised toexamine the literature where they will find ampleuseful and applicable information. They are alsoadvised to consult with their local automotivecoatings supplier where they will find numerousproducts of direct utility. In addition, suppliersof industrial coatings (such as Rustoleum) andequipment fleet finishes (such as Dupont) shouldbe able to provide one with much usefulinformation, free for the asking.

Surface Preparation

The most important step, in my mind, thatcan be taken towards ensuring a good lookingand long lasting paint job is surface preparation.This is where you should spend the most time –applying the paint, from the standpoint of theamount of work required, is almost anti-climactic.

Practically anybody can learn to spray paintbut getting the surface ready is another story.This is where skill, dedication and perseveranceis required. You must decide how much workyou want to put into surface preparation becauseit will have a direct effect on the outcome of thepaint job. A poorly prepared substrate will onlyresult in paint that looks bad and fails early.

Eric Wilde is a software engineer byprofession and a railroad car rebuilder byavocation. He has extensive knowledge aboutrailroad car rebuilding gained over twentyyears of restoration and rebuilding ofstreetcars and railway equipment. Hiscurrent project is the upgrading of a 1950’sPullman-built sleeping car to current Amtrakstandards.

2 1998 January

There are two goals to be achieved inmaking a surface ready for painting: cleanlinessand flatness.

The first is important because the paint muststick to be effective. Consider a typical mode offailure of a ferrous-metal painted surface.Perhaps some minor imperfection or bit of dirt orrust remains behind under the paint film.Expansion and contraction of the metal orvibration leads to a tiny crack due to the paint notadhering properly. The next thing you know,water and air are able to penetrate the paint filmand start to work on the metal. Once these twoculprits start work, the rest is history.

There are other reasons why the paint willfail (flying rocks, for example) but, suffice to saythat, besides being next to Godliness, cleanlinessis extremely important when paint is to beapplied.

Flatness is important because most surfaceirregularities will show or telegraph right throughthe paint. Think about the dry film thickness ofmost paints: prime coats are typically 1.5-3 milsand top-coats are typically 1-1.5 mils. Perhapsthe whole paint job adds up to a layer 6-9thousandths of an inch thick. That’s not going tohide much, is it?

Another reason to strive for flatness is toavoid paint failure. At any sharp edges or abruptchanges (the edge of a pit or chip, for example)the paint film is thinner, due to the effects ofsurface tension (did you ever notice how difficultit is to get paint to cover the sharp edge of a pieceof metal or something similar – rounded edgesand smooth transitions are much easier to cover).Add to this the increase in mechanicaldisturbance of the paint, caused by the sharpedges that it is applied to protruding into the fray,so to speak (e.g. exterior paint is constantly beingimpinged upon by the passing air-stream loadedwith abrasive dirt) and you have a recipe forearly failure.

Flatness of the surface is not to be confusedwith smoothness, however. On the grand scaleor macroscopic level, smoothness is desirable butdown at the microscopic level a certain amountof surface roughness or tooth is important. Thetooth gives the paint something to stick to. Thisis the reason for lightly sanding pre-existing paint

(to break the glossy sheen which is very smooth)or for etching new metal (to roughen the perfectmill finish) before applying paint. It is also thereason for sanding between coats of paint, if along period of time has elapsed betweenrecoating (within the recoat time, succeedinglayers of paint adhere to prior coats chemicallybecause the prior coat is not completely cured).

Achieving Surface Readiness

The coatings industry has categorizedsurface preparation treatments for metal objects(primarily steel) based on the quality of thesurface achieved (see Table 1). Not all paintsrequire the highest level of surface preparation(although it never hurts). Paint manufacturerslong ago realized that surface preparation is thebiggest cost in a paint job and so they haveformulated paints for different applications.Some, like red-lead, are amenable to beingapplied directly over bird-shit, while others, likecertain epoxies, prefer a surface that the FDAwill let your customers eat off of.

Deciding what type of paint will be applied,ahead of time, will indicate what type of surfacepreparation is necessary. The applicationinstructions usually specify what is required (ifthey don’t, ask the manufacturer). Various paintsare formulated to be applied over existing paint,rust, new metal, etc. (See “Paint Selection” formore help).

At the very minimum, anything loose orflaking such as dirt, heavy bird-shit, rust, greaseand oil, old paint, etc. should be removed. Thiscan be accomplished by hand wire brushing,scraping, needle-scaling, power washing orrunning the car down that branch-line with thelow joints. Whatever will knock things loose.

The next level of surface preparationinvolves wire brushing with a power tool (usuallythe infamous angle grinder). My personalfavorite brush is the cup wheel but a straightwheel is useful too. An aggressive wheel such asa knot wheel will remove dirt, loose paint andrust much better than a straight crimp type. Youshould wear a dust mask and safety glassesbecause lots of small particles will fly off duringthis operation as well as pieces of broken wirefrom the brush.

1998 January 3

Using the wire brush, you can removeeverything that’s loose or you can go right downto bare metal. I find that wire brushing doesn’treally remove everything, no matter how hard Iwork. At a certain point it starts to spread things

around and blend them together. If completelybare metal is what you want, sand-blasting is theanswer.

Without a doubt, sand-blasting is theCadillac of the surface preparations. Using a

sand-blaster, it is possible to render an itemsurgically clean. Not only that but the minutepits left in the surface of the metal by the impactof each grain of sand provide an excellent toothfor the paint that follows. Sand-blasting is messy

and time-consuming but it produces wonderfulresults. Appendix A describes different types ofsand-blasting equipment and how it is used.

There are several different grades of sand-blasted surface preparations, as can be seen from

Rating Name Description

SP1 Chemical Cleaning Use one or more of the following techniques:Cleaner/Degreasers: for removal of grease, oil and dirt. Apply directly to surfaceand rub with cloth, sponge or stiff bristled brush.Steam Cleaning: for removal of grease, oil, salt, acid, alkali and similar chemicalresidue. For maximum effectiveness, use in conjunction with Alkaline Cleaning.Alkaline Cleaning: for removal of dust, dirt, wax, grease, oil, fat, salt, acid residue,etc. Scrub surface with a strong detergent such as Trisodium Phosphate (TSP).Volatile Solvent Cleaning: Apply solvent to surface with cloths and scrub to removegrease and oil. Several successive wipings with clean cloths and fresh solvent areusually necessary. For best results follow with Alkaline Cleaning.The surface must be rinsed thoroughly with water and be completely dry before theapplication of the coating.

SP2 Hand Tool Cleaning Scrape with a hand wire brush for removal of loose rust, loose mill scale anddeteriorated coatings. Prior to scraping, remove grease, oil, salt, chemicals, dirt andother contaminants by Chemical Cleaning.May require Commercial Grade Blast Cleaning for problem areas.

SP3 Power Tool Cleaning Wire brush with a hand-held angle grinder, etc. for removal of loose rust, loose millscale and deteriorated coatings. Prior to wire brushing, remove grease, oil, salt,chemicals, dirt and other contaminants by Chemical Cleaning. Care should be takennot to polish metal surfaces or abrade them too deeply.Sound coatings which are very hard or glossy should be sanded to remove gloss.Examine carefully for signs of rust beneath coating and remove, if present.May require Commercial Grade Blast Cleaning for problem areas.

SP5 White Metal BlastCleaning

Complete removal of all mill scale, rust, rust scale and previous coating by abrasiveblasting. Surface will have a dull, gray/white appearance.

SP6 Commercial Grade BlastCleaning

Removal of at least 66% of all mill scale, rust scale and previous coating from eachsquare inch of surface area by abrasive blasting. Shadows and/or streaks caused byrust stain and mill scale oxides may be left behind.

SP7 Brush-Off BlastCleaning

Removal of loose rust scale, loose mill scale and loose coatings by abrasive blasting.Tightly bonded material may be left in place.

SP10 Near-White BlastCleaning

Removal of at least 95% of all mill scale, rust scale and previous coating from eachsquare inch of surface area by abrasive blasting so that only slight discolorationremains but surface is otherwise free of all visible residues. Only light stains andsmall specks of previous coating may be left behind.

SP11 Power Tool Cleaning toBare Metal

Power tool cleaning to produce a bare metal surface. This specification exceeds SP3in that it requires complete removal of all visible oil, grease, dirt, dust, mill scale,rust, paint, oxide, corrosion products and other foreign matter. Slight residues of rustand paint may be left in the lower portions of pits.

Table 1: Recommended Surface Preparation From The Steel Structures Painting Council

4 1998 January

Table 1. Essentially, each grade depends on howmuch time you want to spend. Simply removingthe loose material and dirt with the sand-blasteris very quick but yields the minimum surfacepreparation. Removing the majority of thematerial on the surface yields a much bettersurface while removing everything and blastingthe metal until it is uniformly gray/white yieldsthe best surface preparation.

In difficult situations, where rust is presentbut it is not possible to wire brush or sandblast,rust reformers may be useful. Although it isdoubtful that we will ever be able to truly reformrust’s nasty ways, these products can help to putit in its place for a while. Most of them containphosphoric acid and come as a heavy liquid. Youpaint them onto the rusted surface and theyconvert the iron oxide to a stable form thatprotects the underlying metal and is suitable forpainting. Not an ideal solution (the idealsolution is to remove the rust) nor one thatshould be used everywhere but one that iscertainly handy in a pinch.

Dealing with existing paint on a surface isalso necessary because most of the equipmentone sees has been painted before, sometimesmany times. The old paint should be examinedcarefully to determine what condition it is in.Look for cracking, peeling, blisters, pin holes,chips, etc. If it is found to be intact and adheringto the surface, there is no need to remove it. Ifthe paint lasted this long, it is protecting what isunderneath just fine.

Normally, old paint that is to be left in-situ issanded to prepare it for painting. Start work onthe old paint by sanding off anything that’s roughor loose. Sandpaper around 80 to 100 grit can beused for this step, followed by 120 grit. Next,move up to 150 grit and smooth everything out.My favorite tool for this step is a palm sanderwith Aluminum Oxide sandpaper but you mayprefer a random orbit sander with SiliconCarbide paper or something else. A discussion ofsandpapers can be found in Appendix B and thisshould prove useful for selecting the right paperfor the job.

As mentioned in the previous paragraph, twotypes of sanders that can be used are the palmsander (accepts a 1/4 sheet of sandpaper) and therandom orbit sander (accepts circular disks ofpaper, usually stuck in place with pressure

sensitive adhesive). Both of these sanders areuseful to give a surface its final preparationbecause they move the sandpaper in a fairlyrandom pattern producing small swirls that aren’tvisible under the paint.

For heavier sanding, a jitterbug sander maybe more useful. This type of sander accepts a 1/3sheet of sandpaper and can be used to removelarge amounts of material. The pattern ofscratches left behind, however, is not conduciveto immediate painting. Similarly, an orbitalsander (using circular sanding disks) can beemployed to aggressively remove material butthe pattern of scratches left behind will alsotelegraph through the paint.

For large areas (such as a side-sheet) thatneed to be rendered flat and level without smallundulations, a stroke sander is just the ticket.This sander accepts a long strip of paper that cancome on a roll or in pre-cut lengths. Its long baseremoves small bumps and so on and renderseverything flat. This sander should be used firstfollowed by one or more of the other sanders tofinish off the surface.

Most sanders can be purchased in electric orair-powered versions. If you have thecompressor available, air-powered tools tend tobe smaller and cheaper than electric tools. Thereis often much more choice in the air-tool line too.

One word of caution is in order here. If youare going to be doing a lot of sanding, get a pairof anti-vibration gloves and wear them.Otherwise, you may find yourself the victim ofan affliction known as white-hand – the fingersstart to tingle and go numb followed by turningwhite of the hand and fingers and then loss of allsensation. If left unchecked long enough, I’mtold that the loss of sensation becomespermanent.

The idea of sanding is to make everythingflat (as mentioned before). Typically with oldpaint, there are chips, scratches, dings, and so onthat need to be addressed. With chips andscratches, the paint should be feathered out sothat there are no abrupt changes in altitude.What does feathering mean? Simply that thethickness of the existing paint varies graduallyfrom its full thickness down to zero thickness atthe surface of the bare metal like the edge of abird’s feather. How do you tell when the paint isfeathered properly? Easy! Look at the old

1998 January 5

paint’s edges and make sure that they are broadbands. If there are several colors, each colorshould change from one to the next in a broadband. Any narrow bands indicate a sharptransition. What constitutes a broad band?Perhaps 1/4 - 3/8”, depending on the thickness ofthe paint film.

Removing Old Paint

There may come a time in the life of someor all of your previously painted surfaces whenstripping may be necessary. There are a numberof reasons to strip (unsightly paint buildup,obscured details, environmental reasons [i.e.

lead] or spectacularly failed paint film). The bestadvice that I can give about stripping is, “leave itfor the next guy”.

Often, you can repaint a surface withoutstripping, if the paint on it is sound. If thesurface can be tuned up a little by feathering out

chips, spot-priming, etc., this is the way to go.On the other hand, if new paint is applied overold, poorly-adhering paint, the potential fordisaster is very real. So, how do you know forsure whether the old paint is solid? U.S. Paintrecommends the steps detailed in Chart 1 to testthe existing paint. If your paint passes all of the

1. If old paint is peeling extensively, heavily chalked (chalking is when the paint turns to powder, like chalkdust, and is washed away by rain), blistered or cracked, it fails the test.

2. If there are obviously corroded or blistered spots, soft spots or other indicators of corrosion, the paint is nogood.

3. Perform a cross hatch adhesion test as follows:

a) Select a test area on the surface to be painted and thoroughly clean, de-wax and degrease this area.

b) With a razor blade, scribe a 2" x 2" area in a 1/4" cross hatch pattern (this should look like a checkerboard). The cuts must be deep enough to reach the surface.

c) Apply a top-quality plastic filament packing tape (masking tape isn’t acceptable) over the scribed area,making sure that the tape adheres tightly to the paint.

d) With an abrupt yank, pull the tape back parallel to the surface. Pulling straight up will not test the paintproperly.

e) Examine the test surface. If any square of old paint in the scribed area was removed, the paint fails thetest.

4. Perform a solvent resistance test as follows:

a) Saturate a cotton ball with the reducer used to thin the paint to be applied.

b) Tape the reducer saturated ball over the scribed area for 30 minutes.

c) Remove the ball and examine the old paint. If it has been dissolved or severely softened, it isincompatible and the paint fails.

d) Allow a 15 minute recovery period and then perform the cross hatch adhesion test detailed in step 3again.

5. Perform a coating compatibility test as follows:

a) Select a new test area and lightly sand it with 220 grit sandpaper. Clean the sanded area, as appropriatefor the paint to be applied.

b) Paint this area with the paint to be applied.

c) Allow the paint to cure for the proper amount of time necessitated by the ambient temperature (e.g. 24hours at 70 degrees).

d) Perform the cross hatch adhesion test detailed in step 3, on the new test area to check for inter-coatadhesion.

Chart 1: Existing Paint Fitness Tests

6 1998 January

tests, it is a good bet that it is sound, whereas, ifit fails, it undoubtedly isn’t.

If you do decide to strip, there are severaltechniques, available: mechanical, heat,chemical, and freezing.

“Mechanical” means scraping, sanding,abrasive blasting or wire-brushing. Wire-brushing should only be done on surfaces thatcan stand the gaffe (i.e. don’t even think of usingit on aluminum) because the brush will try tochew up more than just the paint. Sandingshould be reserved for the last pass over thesurface because old paint tends to load up thepaper and clog it (although stearate paper canhelp) and there are admittedly faster ways toremove paint. Similarly, abrasive blasting isbetter suited to removing rust, loose paint, etc.rather than stripping layers of old paint.

Which leaves scraping, that ancient, triedand true method. Not much has changed in thetechnique used for scraping since the good olddays, although the introduction of the carbidescraper (mine are by Sandvik and they feature areplaceable slug which stays sharp longer andcan be tuned up on the side of a green grindingwheel) means that you can scrape longer andremove paint easier than with a traditional springsteel blade. The one modification that I make tothe carbide blade is to grind (once again, with agreen wheel) a slight bevel on the ends of theblade so that it won’t make gouges in anythingsoft (e.g. aluminum). Gouges are to be avoidedat all costs because they may prove downrightdifficult or even impossible to remove by sanding(requiring filling to remove).

Scraping by itself, isn’t going to get youanywhere but frustrated. The paint needs to beconvinced that it should come off with thescraper. To do this, one uses either heat orchemicals.

Heat can be supplied by one of the manytypes of electric heat guns. I use a 1” diameternozzle and run the sucker on high. It isn’tnecessary to wait until the paint blisters – it willbe soft enough to scrape long before thathappens. Pay particular attention to ply-metal.Too much heat can cause de-lamination of thethin aluminum skin. I have also seen problemsarise with items such as doors (due to cut-outs formirrors), etc. Heating the tiny bit of remaining

material on the obverse side of the cut-out causeswarping and the door no longer closes.

With sheet aluminum, the heat is suckedaway from the spot being heated and the metalbuckles well before the paint begins to soften.While the buckled metal usually returns to itsnormal shape, the bulge or indentation that iscaused can render scraping very difficult. Metalssuch as carbon steel and stainless don’t exhibitthese problems and are usually easy to scrapewith the assistance of heat.

If you are faced with a tough problem,chemicals may be the answer. There are twogroups of chemicals used for stripping paint:organic solvents; and caustic compounds. Theorganic solvent of choice is methylene chloride.The caustic compound of choice is sodiumhydroxide. Here is a little more informationabout each.

Organic strippers usually contain methylenechloride (a toxic, carcinogen – isn’t everythingthat works a toxic, carcinogen?) in varyingproportions and work by dissolving the old paint.Other ingredients in solvent-based paint strippersare acetone, toluene and methanol, N-methylpyrrolidone (NMP) and dibasic esters (DBEs)such as dimethyl succinate ester and glutarateester (see Table 2).

If a stripper doesn’t contain methylenechloride, it probably won’t work very well. Onecould argue that some of the other organicsolvents are pretty good paint strippers but whymess with success? Methlyene chloride works.The only other thing that needs to be mixed withmethylene chloride to yield a good paint stripperis a small percentage of wax (say 10%) toprevent the volatile liquid from evaporatingbefore it has a chance to attack the paint.Everything else in a paint stripper is usually justcheap filler. So, the rule is generally, the moremethylene chloride, the better the paint stripperand the more expensive it is.

A cautionary note is in order. Methylenechloride attacks aluminum and, in the process,yields an explosive gas. Its not as if your ply-metal will be instantly turned into plywood but,aside from the toxic and carcinogenic propertiesof this stuff we add explosive gas (methlyenechloride by itself is not flammable but when cutwith acetone, toluene or methanol, the resultingwitches brew is). Methlyene chloride evaporates

1998 January 7

quickly and the vapors are easily inhaled andabsorbed into the bloodstream where they cancause a host of problems, not the least of whichare dizziness, headache, heart and lung problemsand liver and kidney damage. Maybe workingoutside or in a well-ventilated area is a good idea.

Caustic compounds are those such as Peel-Away that contain alkalis. They work by

breaking down the old paint into a soft goo. Thegoo is then stabilized by applying a sheet ofplastic after which it can be peeled away in onesheet (no scraping here). They are usuallyformulated “for use on aluminum” and “for useon everything else”. Once the paint is strippedaway the surface must be neutralized by a mild

acid (such as household white vinegar). After thesurface is neutralized, it should be flushed withwater to remove the residue and cleaned up bysanding, if necessary.

Again, caution is in order when using causticstrippers. Although there's no danger ofexplosion or toxicity, these products contain verystrong caustic compounds that can produce

severe burns, should they come in contact withskin, blindness, should they get in one's eyes, etc.Wearing rubber gloves, long-sleeved shirts,goggles and other protective gear is more thanjust prudent (see Appendix C).

Cleanup is also an area to give considerationto. Caustic paint strippers work by literally

Product Contains Remarks

ParksEco Strip

30-45 mins, 10-15 coats.Oil-based and latex paints.Non-flammable, low vapor toxicity, semi-paste.

ParksPro Stripper (1513)

Methylene ChlorideFive other organic solventsAmmonia

10-20 mins, 10-15 coats.Oil-based, epoxy and polyurethane paints.Strong, non-flammable, toxic, fast-acting, semi-paste.

ParksLiquid Strip (1553)

AcetoneIsopropanolTolueneHexaneN-Bytyl-acetate

10-15 mins, 4-5 coats.Oil-based paints.Liquid formula penetrates cracks, details and difficult toreach areas (great for soaking parts). Extremelyflammable.

Klean-StripPremium Stripper (KS-3,KS-221)

Methylene ChlorideIsopropanol and MethanolEthylene GlycolMonobutylether

10-30 mins, 10-13 coats.Epoxy, polyurethane, oil-based and marine paints.Strong, non-flammable semi-paste (KS-3) or sprayable(KS-221).

Klean-StripEasy Off Stripper (WC-203)

Citrus oils 3-30 hrs, 10 coats.Oil-based and latex paints.Non-flammable, non-toxic, semi-paste.

Klean-StripHeavy-Bodied (HB-2)

10-30 mins, 5-6 coats.Oil-based paints on metals.Non-flammable, medium viscosity.

Citristrip N-Methyl-2-Pyrrolidoned-Limonene

Stays wet up to 24 hours.Combustible, skin irritant.

Dumond ChemicalsPeel-Away (ST-1)

Sodium Hydroxide 24 hrs, coats up to 40 mils.Alkyd and latex paints on steel.Non-flammable, caustic.

Dumond ChemicalsPeel-Away (ST-2)

24-hrs, coats up to 40 mils.Alkyd and latex paints on aluminum.Non-flammable, caustic.

Nu-Tec IndustrialChemical Mfg.Nu-Tec Paint Stripper

Four organic solvents 3-4 hrs, coats up to 40 mils.Alkyd, epoxy and polyurethane paints.Skins over on application and reverses the solvents backinto the paint, flammable, sprayable.

Table 2: Examples of Commonly Available Chemical Paint Strippers

8 1998 January

liquefying old paint. When you pull away thebacking sheet, most of the old paint will comewith it but some liquid will remain behind on thesurface. You will need lots of paper towels towipe it off, a container to safely dispose of thestill-caustic waste, neutralizer and plenty ofwater to flush the surface with to rinse it off.And, keep in mind that this whole process ispretty messy so don’t attempt it in areas wherethe mess could pose a problem.

The last method for removing old paint isapplicable to painted metal surfaces, especially

ply-metal and aluminum. It involves freezing thepaint with liquid nitrogen which causes the paintto shrink more than the metal and becomeextremely brittle. The stresses from shrinkagecause the paint to crack, making it easy toremove from the underlying surface. The residueis a dry powder that can be swept or vacuumedup. If you are interested in this method, contactone of the industrial gas suppliers for moreinformation.

Repairing Surface Imperfections

Ding’s and other divots need to be filledwith Bondo (a commonly used name for plasticautobody fillers) or some other type of filler.Large holes may require kitty hair Bondo (fillerwith chopped up fiberglass added to it forstrength) or a fiberglass patch, although I preferto cut out any rot and replace it with new sheetmetal or build up decayed structural members bywelding and reinforcement.

Most plastic fillers contain a filler material(such as plastic micro-spheres) in a styrenemonomer base. When a catalyst (usually benzoylperoxide) is added to it, the monomer reacts andcures to create a hard, plastic polymer. Fillerswith fiberglass chop often employ a differentbase than the plastic fillers, one that uses methylethyl ketone (MEK) as a catalyst.

The higher quality plastic fillers are usuallyworth their premium price (see Table 3) becausethey offer superior workability, sandability andadhesion. They may even incorporate the ability

to etch the metal that they are applied to(promotes adhesion) and resist bleeding throughthe paint sprayed over them. In short, usingcheaper fillers will probably not gain oneanything but grief.

Bondo should be applied in thin layers ratherthan trowelling it on heavily because the settingmechanism is an exothermic reaction and thebuild up of heat caused by using large amounts ofBondo can cause cracking or weakness.Applying it in thinner layers takes longer butensures a better patch. The color of the activatorcan be varied to show the different layers, as theyare applied.

Before applying Bondo, the surface must beclean and dry. It doesn’t hurt to roughen thesurface a bit and it is even a good idea to drillsome holes in large areas so that the Bondo willhave something to grip.

Filler Price Rating Viscosity Cures Sandability

3M High Excellent Thick Quickly Excellent

Platinum High Good Medium Quickly Good

Bodyman’s Request Low Fair Thick Quickly Good

Body Pro Low Fair Thick Quickly Fair

Feather Rite Moderate Fair Thick Quickly Fair

Golden Extra High Poor Medium Slowly Poor

Marson Low Poor Thick Average Poor

White Lightning High Poor Thin Average Poor

Table 3: Plastic Fillers

1998 January 9

Immediately after applying Bondo, cover itup or prime it, if it will be outside. ExposedBondo will absorb water which can causeproblems for the paint film later on (think aboutsteam forming under a layer of paint on a hot,sunny day).

Repairing Sheet Metal

Replacement sheet steel can be welded intoplace with a MIG welder. The edges of the cutsheet should be beveled to form a vee where theymeet or they may be bent inwards on thinnersheets. A straight butt weld applied to thesurface of the sheet will have most of the weldbead ground away when it is flattened later on,hence the reason for the vee. Magnets can beused to hold the sheet in place and to line theedges up while it is tacked. Skip welding will tieeverything down before the final weld pass andprevent buckling. Car sides and other parts oflightweight steel cars were usually made of #16gauge hot rolled steel. I keep a sheet of this stuffhandy (it is very cheap) for patching and it seesplenty of use.

Fresh welds should be ground flat with thesurrounding surface. I use an angle grinder witha stone for very rough work and then finish it offwith an 80 grit sanding disk (if you want thelatest, killer product for grinding sheet metal, tryone of the layered flap wheels such as the TigerDisk made by Weiler. They are expensive butlast a long, long time. Use the next grit down[i.e. 60] from what you’re used to in a sandingdisk).

Lay the sanding disk flat against the sheetand move it back and forth constantly to ensurethat the surface will be smooth and even and thatthere won’t be any gouges. The Tiger Diskworks especially well for smoothing andsculpting and you will find that, with practice,you can produce nearly invisible patches andrepairs.

The last step, after applying a sheet metalpatch, is to fill any irregularities with Bondo. Ofcourse, if you were paying attention to the lastparagraph about sculpture and you were thinkinglike Renoir, you won’t be needing much Bondo.But, even if you didn’t create a work of art, youcan work carefully with the Bondo to lineeverything up and achieve a patch that is virtuallyundetectable. Exercising extra care at this step is

well worth it for the quality of finish achieved inthe long run.

Exotic metals (e.g. aluminum) present moreof a problem, if repairs are necessary. While theexotic metals can be welded, it takes specialknow-how and special equipment (admittedlyaluminum can be MIG welded with the propershield gas but I’ve never been real impressedwith the results).

I usually punt on aluminum and fix it withpop rivets. A counter-sunk rivet can be used topatch holes in an aluminum sheet by attachingthe patch to a backing piece. Strips of backingare first riveted around the edges of the hole sothat they stick out 3/4”. Next, the patch is cut outto fit the hole and then riveted in place. After therivets are ground flush and filled (I use analuminum-powder-bearing epoxy filler calledMetal-to-Metal) the patch is invisible. One tip isto bevel the outside edges of the patch and thehole so that the joint between them can be filledwith a goodly amount of filler. This shouldprevent hair-line cracks later on.

Repairing Ply Metal

The interior walls of many cars areconstructed of a material called ply-metal. Thisis essentially a sheet of plywood (of varyingthickness’) laminated to a thin overlay ofaluminum sheet on both sides.

Prior to painting the interior you may need tomake repairs to ply-metal. It has, in myexperience, two modes of failure. The first iswhen the aluminum sheet de-laminates from theplywood (usually due to the presence ofmoisture). This type of failure can be repaired bycutting out the de-lamination and filling it withanother piece of sheet. The new sheet is glued inplace with Resourcinol glue (a two-part glueavailable from DAP [among others] at betterwoodworking supply stores). If it is a largepatch, I add some counter-sunk flat-head screwsto hold it in place permanently.

The second mode of failure is more seriousand usually results when a great deal of moistureis present (say from a periodically explodingtoilet). In this case, the ply-metal is rotted outand there’s nothing substantial left (a third modeof failure results when the idiots from the moviecompany cut a hole in a wall with a Sawsall, butthat’s another story).

10 1998 January

If the rot is only beginning, one of the liquidepoxy rot repair products may be able to stabilizeit. If so, the de-laminated sheet may then bepatched (as described in the preceding paragraph)or a heavier piece of aluminum plate may be

spliced into the good plywood to providereinforcement.

Replacing a missing or totally destroyed ply-metal wall presents two problems. One is toremove and re-install the wall (railway

Paint Examples Composition Remarks

Epoxy Dupont 25P, Corlar 26PRustoleum 9100, 9300Griggs DC733Anchor 3900, 3950Ben Moore M33/M34

Catalyzed epoxy resins

Acetone, MEK or otherketone solvents

Tough, impermeable, long-lasting. Excellentlong-term solvent, chemical and abrasionresistance. Used for priming and surfacingunder high performance coatings. High-buildcan fill small surface irregularities and pits.

Polyurethane Dupont Imron 326, 333Rustoleum 9400PPG DCCUS Paint AlumigripGriggs MIL-C-83285B,

MIL-C-83286BAnchor Ancothane 9400

Two-componentaliphatic polyesterresins (cross-linked byisocyantes)

Hard, super-gloss finish. Superior corrosionand chemical resistance. Extremely impactand abrasion resistant. Longest lasting.Product of choice in transportation industry.PPG DCC and Anchor Ancothane are acrylicurethanes which are even tougher thanpolyurethane.

Acrylic enamel Dupont Centari Similar to alkyd enamelbut modified withacrylic resin

Dries by solvent evaporation, is not stickywhen dry and cures by oxygen absorption.Centari is one of the most forgiving paints.

Industrial Alkydenamel

Dupont Dulux 30P, 31P,34P

Rustoleum Labor SaverBen Moore Iron Clad 163,

M24 DTM

Alkyd resin

VM&P Naptha,Stoddard solvent

Tough, flexible films having excellent colorand gloss retention. Dries by solventevaporation, is sticky when dry and cures byoxygen absorption. Use in mild to moderateenvironments. Periodic recoating necessary.

ArchitecturalAlkyd enamel

Kelly Moore 1625, 1630Ben Moore Impervo 235,

Dulamel 207

Alkyd resin

Stoddard solvent

Interior alkyd enamel can be used in theinterior of equipment with excellent results.

Primer Dupont 25P, Corlar 26PRustoleum (many kinds)US Paint G9072 (ZnCr)Kelly Moore 1710, 1711Ben Moore M06/M07

Formulated to adherelike a bandit to thesubstrate

Can be epoxy, alkyd or acrylic. Special paintslike zinc-selenium for cathodic protection,zinc-chromate for aluminum and others areavailable for solving special problems.

RustoleumDamp ProofRed Primer

Rustoleum 769 Alkyd resin

Fish oil

VM&P Naptha solvent

Used on rusted steel only. Fish oil penetratesrust to the metal and drives out air/moisture.Bonds tightly to rust. May be applied toslightly damp surfaces.

Surfacer Dupont 25PRustoleum high build

9500US Paint D8003, D8002

Formulated for sanding Can be epoxy, alkyd or polyurethane.Surfacers are normally used with automotivefinishes. A high build epoxy can be used onrailway equipment exteriors.

Acrylic Enamel Rustoleum 3000, 3100DTM, 5200

Kelly Moore 1725Ben Moore M04-01, M29

DTM

Acrylic resin

Water solvent

Fast-drying. Better gloss and color retentionthan alkyd enamels. Low toxicity and odoreven in enclosed areas. Easy clean up withsoap and water. Can be applied direct tometal: steel; galvanized steel; aluminum.

Acrylic Epoxy Dupont Corlar 76PRustoleum 5300Ben Moore M08/M09Griggs Hydropox #2

Catalyzed AcrylicEpoxy resin

Water solvent

Fast-drying. Low toxicity and odor even inenclosed areas. Easy clean up with soap andwater. Excellent base for high-performancetopcoats.

Table 4: Paints For Painting Railway Equipment

1998 January 11

equipment is put together like automobiledashboards – in layers – and the layer you’retrying to work on is at the bottom) and the otheris finding new ply-metal.

Removing and replacing the wall is donehowever is necessary. Screws can be cut with athin saw blade, the wood can be cut in half, etc.One method to consider for re-installing the wallis to cut it in half, rout two recesses (beforecutting) to accept an aluminum splice plate,install the wall and then splice and patch it withBondo after installation.

The tools used to work with ply-metal arestandard woodworking tools, although I prefer touse carbide cutters and blades. You may want toreduce the feed rate and/or cutting speed and useblades with a greater number of teeth.Otherwise, I have found ply-metal to be veryamenable to working with portable saws, jig-saws and routers. Also, like plywood, it can bechiseled, planed, etc. Don’t let that aluminumbother you, its like paper anyway.

And speaking of finding ply-metal, where doyou find it? The best source is a company thatsupplies sign blanks to the advertising industry.They will have this sheet in 1/4” and 1/2”thickness and sometimes 3/4”. It comes coatedwith paint (shiny and meant for screen-printingwith ink) that can be scuff-sanded with 320 gritand painted directly (after you peel off the plasticprotective sheet).

If you need other thicknesses, good luck.Some wood shops will laminate it up for you butthis approach is very expensive. Try fabricatingit yourself out of a top-grade plywood andaluminum sheet. The glue to use is Resourcinolor epoxy or maybe polyurethane (something witha long set-up time may be necessary to allow youto get the sheets together) and the clampingmethod of choice is a vacuum press.

In a pinch, you can use MDO plywoodwhich is an exterior type plywood made ofhardwood veneer overlaid with a resin-treatedfiber overlay. Medium density overlays aredesigned with just the right tooth for smoothpaint application, making MDO the preferredpanel for sign manufacturers. Consequently, itshould also be available from any company thatsupplies sign blanks to the advertising industry. Ihave seen at least one car remodeling job donewith this material and, when painted, it makes a

very acceptable substitute for ply-metal, if thereal thing isn’t available.

Paint Selection

All paint consists of pigments, resins andsolvents. The resin is the coating material whilethe pigments determine the paint color and thesolvents reduce the paint to a workable viscosity.Given this basic formula for paint, there aremany different ways to produce useful paints andthis yields many kinds of paint that areappropriate for use on a railway car. The type ofpaint being used will depend on the particularapplication. Table 4 lists most of the paints thatare available and shows some of theircharacteristics. I will discuss the uses of each,where appropriate.

If we start outside the car, the properties thatwe are looking for in a paint are: protectionagainst severe corrosion and abrasion; chipresistance; longevity; resistance to fading; ease ofapplication (i.e. minimal surface preparation);and lowest cost. Pretty impressive list, huh?Good luck finding this miracle coating. Actually,it isn’t possible to meet all of these criteria but itis possible to come close.

When one considers the longevity of acoating and the amount of work involved inpreparing the surface, the cost formula looksmuch different than just the initial cost of thepaint (see Table 5). If this is done, the epoxypaints look pretty good. Epoxy providesexcellent protection against corrosion andexhibits toughness against chipping andscratching. High build epoxies can be used as asurfacer as well as a primer. Although its colorcan fade significantly in a short time, thelongevity of the coating is high (the fading doesnot affect its performance). Epoxy paint is easyto apply (can be brushed or sprayed), but there isa problem with pot life (once mixed, the paintwill harden in a few hours to a few days). Thenet result is that epoxy should be considered forthe exterior of a railway car in all places (roof,sides, underframe, etc.) as a primer andintermediate coat in a 2- or 3-coat system.

The primary problem with epoxy is its colorfading. Although it continues to offer protectionto the painted surface, the aesthetic quality willdiminish rapidly. Fortunately, there ispolyurethane paint which has an unsurpassed,

12 1998 January

long-lasting aesthetic quality. Many paintmanufacturers offer a two- or three-coat systemwhereby polyurethane is applied over epoxy togive a tough, long-lasting and beautiful finish.

Polyurethane’s biggest drawbacks are itscost (perhaps $75-$150 per gallon) and itsdangerous properties. The cost is actuallyexcellent, if you consider longevity but there isno getting around the danger. Basically,polyurethane is poisonous (remember the methyl-

isocyanate leak in Bhopal – same stuff). Itcomes in two parts (the paint and the activator)and before, after mixing and until it has cured,the vapors or atomized paint must not bebreathed. Application must be done whilewearing a supplied-air respirator with a full-facemask and there must be a good supply of freshair to disperse the vapor. No kidding! I’ve seenpeople get very sick just from breathing a smallamount of residual vapor.

Inhalation of isocyantes may sensitize aperson, causing an asthma-like reaction. Thereaction may occur within days of exposure ormay take months or years to develop. Oncesensitized, a person is likely to experiencerecurring shortness of breath upon repeatedexposure. Direct skin contact causes rashes,blistering and reddening. Repeated contact maycause skin sensitization. Exposure to airborneisocyanates can cause eye irritation andtemporary blurred vision. Direct contact with theeye may cause cornea damage, hence the needfor a full-face mask, supplied air respirator.

Polyurethane essentially is plastic that youmake at the site. Once you mix it, it’s going toturn into plastic, one way or another. The pot lifeis about eight hours (shorter on hot days) so onlymix what you need. Furthermore, it cures byabsorbing water so it must be kept dry whilecuring (roughly four hours). If the paint gets wet(this includes condensation as the sun sets as wellas the more obvious sources of moisture such asrain), it will go nuts – you won’t like what

happens.

Other than these little problems,polyurethane sprays pretty much like regularpaint (it is thin so it levels exceptionally well butit will not hide sharp edges and may form runsand sags easily) but it cannot be applied anyother way except by spraying. Once it is on, thefinish cures to a hard, glossy surface that looksgood for a long, long time. Many car ownersconsider this paint to be the finish of choice forcar roofs and sides.

If polyurethane makes you nervous (or poor)you might consider acrylic enamel instead. Ihave seen several beautiful paint jobs done withDupont Centari and there are some proponents ofit who claim that it effectively lasts just as longas polyurethane – it certainly is more amenableto the repair of rock chips, scratches, etc.

Enamel (either alkyd or acrylic) can be usedanywhere and it is very easy to apply, with brushand spray being the preferred applicationmethods. The main disadvantage of enamel is

Paint/Surface Prep Service Life Initial Cost per Foot

Surface Prep Application Paint Total

Cost perFoot per

Year

2-Coat AlkydHand Tool Clean

2 yrs $0.49 $0.41 $0.10 $1.00 $0.50

3-Coat AlkydHand Tool Clean

4 yrs $0.49 $0.61 $0.15 $1.25 $0.31

3-Coat AlkydCommercial Blast

7 yrs $0.82 $0.61 $0.15 $1.58 $0.23

1-Coat EpoxyHand Tool Clean

5 yrs $0.49 $0.26 $0.22 $0.97 $0.19

2-Coat Epoxy,1-Coat PolyurethaneNear-White Blast

12 yrs $0.98 $0.84 $0.31 $2.13 $0.18

Table 5: Coating Cost per Year of Service Life

1998 January 13

that it doesn’t last as long as epoxy and it mayfade in color. Otherwise, it is safe and easy touse and relatively cheap to purchase (althoughmore expensive, if application costs areconsidered – see Table 5).

The acrylic enamels, such as Centari, maybe used with a hardener which alters theirdurability to be more like that of polyurethane(many automotive shops swear by this system).Unfortunately, this hardener is a cyanidecompound so the danger associated with usingthis paint increases significantly to the pointwhere it is similar to that associated withpolyurethane. I have had many auto-body guystell me that they spray paint with hardener andeven polyurethane with only an organic vaporrespirator but I wouldn’t try it.

Regardless of the kind of paint that will beused for the finish coat, once the surface isprepared, the first one or two coats of paintshould be primer. The primer stops corrosionand glues itself to the surface (some primerscontain special additives such as fish oil topenetrate rust and stop it. In any case, all primerscontain additional binders to adhere them to thesurface being painted). A second coat of primer,perhaps a contrasting color, may be applied foradded protection.

If you want the finish to look extra good,follow the prime coat or coats by one or morecoats of surfacer. The surfacer is designed to besanded to produce a very smooth finish to whichthe top coat is applied. This step is common inthe automotive refinish business but probably isunnecessary for the exterior of railwayequipment, especially if epoxy or high buildepoxy primers are used.

In general, the primer is chosen to work withthe top coat. The recommendations of themanufacturer should be followed but here are afew rules of thumb. A primer can be like its topcoat (e.g. alkyd/alkyd). Epoxy is generally goodunder anything, especially polyurethane. So isalkyd, given a good chance to cure (say for amonth). For acrylic enamels such as DuPontCentari, an epoxy primer may be used instead ofan enamel primer.

The top coat or coats are applied to seal theprimer and yield the final finish and color (mostfinishes will cover in one coat but a second coatmay be necessary to achieve proper hiding – the

primer can also be selected to be close in color tothe top coat to aid with hiding).

Car interiors can be painted using the samekinds of paint as noted for car exteriors (althoughpolyurethane is not really appropriate). Epoxiesmake good, long-lasting finishes in critical areassuch as kitchens where frequent scrubbing islikely but be sure to choose a paint that isacceptable to the FDA for incidental food contactareas.

The remainder of the car’s interior surfacescan be painted with a good quality alkyd housepaint (using house paint allows you to get anycolor that you want, tinted by your paint dealer).You will probably want to spray this finish sochoose one that levels well without orange peel.Not all house paints will do this, but I have foundBenjamin Moore Impervo Satin to be excellent.If you aren’t sure, get a quart mixed up and try itto see.

For interior surfaces, they consisting mostlyof aluminum in lightweight cars, you may wantto use a primer meant especially for aluminum onany new (or stripped) surfaces. I prefer zinc-chromate primer and apparently so did the carbuilders because they seemed to apply it to everypiece of aluminum on the cars I’ve seen. Eventhe backs of aluminum sheet in walls and otherplaces were given a coat for added protection.Other primers may be acceptable for use onaluminum (if in doubt, contact the manufacturerof the intended paint) but this isn’t true in allcases. Zinc-chromate will take a bite out ofaluminum, forming a permanently-adheringfinish which is what we want, isn’t it?

A direct-to-metal acrylic paint also workswell as a primer for aluminum. I have hadsuccess with Rustoleum's 3081 water-basedacrylic primer applied under alkyd house paintsin car interiors. This kind of paint is great forpainting during winter time when fast dry time(i.e. while the heat is on) and no possibility ofgood ventilation is a requirement.

Estimating Paint Needs

Once you have selected the paint that youwish to use, you should check the manufacturer'srecommendations for dry film thickness andcoverage. Using these figures and the desiredthickness of the film that you wish to apply, youcan determine how much area a given quantity of

14 1998 January

paint will cover. Thicker films will provide moreprotection but will also require more paint andresult in a corresponding reduction in the areathat can be covered.

You should estimate the entire surface areato be painted by breaking it down into smallerconstituent parts whose surface area can beestimated (see Chart 2). Calculate the surfacearea for each constituent part and then add themall up to arrive at a total. Don’t forget to leaveout cut-outs such as windows.

The amount of paint necessary is the totalsurface area divided by the practical coverage ofthe paint. This will give an estimate of howmany gallons of paint to buy, have tinted, etc.Remember that the type of paint gun used tospray the paint can have a large effect here.Depending on whether it is a traditional or HVLPgun, it may put up to 50-60% of the paint into theair, not on the surface being painted (seeAppendix E).

Final Preparation

Now that we’ve prepared the surface forpaint and selected the paint to use, we’re ready toapply the paint – almost. Before you start, checkthe weather forecast (if painting outdoors),prepare the area for painting and get everythingready to go. Once you start painting, stopping toscrew around isn’t good. Unless there is anatural place to break off painting, stopping willproduce lines or obvious joints.

I am assuming that you will be applying thepaint with a spray gun so we’ll proceedaccordingly (scope out Appendix E for moreinformation on spray guns). First check over thesurface to be painted for any minorimperfections, etc. and repair them. If the recoattime has passed on a previously painted surface,

lightly scuff sand it to break the gloss and givethe next coat of paint some tooth to stick to.

Wipe down all of the surfaces with cleanrags and solvent. You should use the two-ragmethod to perform this step. First, wet one ragwith solvent (each paint manufacturer has aspecial solvent that they recommend for this jobbut mineral spirits work well) and wipe off anarea about 4 square feet. Next, before the solventevaporates, wipe it off with a second, clean rag.Repeat this process over the whole surface usinga clean section of both rags on each new area.When a rag becomes dirty, throw it away andalways ensure that the first rag is wet, not justdamp, with solvent.

If the surface is really dirty, wash it with anindustrial type detergent and rinse it off with lotsof clean water. For new or shiny metal, you maywant to etch it with a mild acid (such as MetalTreat) to give it tooth (rinse well and wipe offany powder that forms) or you may want to use aself-etching primer such as DuPont Variprime.Automobile manufacturers next apply a zincphosphate acid treatment to new steel followedby another rinse to remove the acid. If you dothis step it will provide extra corrosion protectionand improve paint adhesion. Finally, the surfaceis allowed to dry thoroughly.

Clean up any dirt and dust that surrounds thearea being painted (the spray gun will blow itonto the fresh paint where it will surely stick –not the desired effect). Vacuum and/or wash anyfloors next to walls and wet down any loose dirt(outdoors). Mask off any areas where over-sprayis likely (and even some where it isn’t) usingpainter’s masking tape and masking paper.

Tape any striping or other details that are tobe left a prior color. Always try to paint stripesand such, where practical, from a lighter todarker color (e.g. paint a yellow stripe first andthen paint the blue surrounding it next).

Give all of the surfaces to be painted a finalonce over to make sure that there is no dirt ordust to mar the paint job remaining anywhere. Apainter’s tack rag should be used as a final wiperag, at the very last moment before spraying, toremove any dust.

Get out all of the supplies that you’ll need:paint; activator; solvents; rags and paper towels;paint gun; etc. Set up your ladder or scaffold, ifnecessary, at the first spot to receive paint. Drag

Shape Area Formula

Rectangle/Square length * widthTriangle height * base / 2Circle radius * radius * 3.14Sphere radius * radius * 12.56Cylinder diameter * height * 3.14Pipe diameter * length * 3.14

Chart 2: Areas of Various Simple Shapes

1998 January 15

out the air hoses and position them to reach thejob.

Before you begin spraying, it is a good ideato take care of your bodily functions, eat lunch,etc. Once you get started, stopping to dosomething else can cause problems with thefinished look.

If you’ll be spraying polyurethane paint,hook up the supplied-air respirator (see AppendixD for more about respirators). I position thecompressor for mine about 150 ft. upwind ofwhere I’m painting and I’m still alive but be sureabout this because, if you smell almonds, you’rein trouble. With most paints, it is a sound idea towear a respirator at all times (even alkyd enamelscan cause a sore throat, dizziness and nausea) soget in the habit of putting it on before you openthe paint cans.

In addition to a respirator, consider wearinggloves and some kind of body protection such asa Tyvek suit or, at a minimum, a long-sleevedshirt and long pants (bear in mind that manyorganic chemicals can be absorbed through theskin, including many of those chemicals used inyour favorite paint). The gloves that I prefer arenitrile and they look like dishwashing gloves.They have the best tactile feedback that I’vefound (one word of caution – lacquer thinner andketones such as acetone and MEK will softenthem in a few minutes rendering them easy totear). Before you don the gloves, blow them uplike a balloon and squeeze them shut at the cuffs.If they won’t stay inflated, toss them out and geta new pair (see Appendix C).

Paint Mixing/Reducing

Open up the paint can and stir the paintthoroughly to ensure that the pigment and resinsare distributed evenly. Do this even if the paintwas mixed mechanically beforehand. Someepoxies may require that the activator be stirredalso. Always use separate tools to mix andmeasure paint and activators. A tiny bit of eitherone can contaminate an entire can of the other(unless, of course, your goal is to make someplastic curling stones).

Pour the paint and optionally the activatorinto the paint pot through a strainer. Strainingwith a paper filter cone is an easy way to ensureno surprises (e.g. a gun clogged by some foreignmaterial and filled with rapidly setting paint). A

filter costs 15-20 cents per use and they are easyto find (most big paint stores sell them in boxesof 100). Compared to fifty or a hundred bucks agallon for paint, a few cents for a strainer is acheap insurance policy.

Try to mix only as much paint as you’ll needor feel comfortable spraying. As you go, you’llget an idea of what kind of coverage to expect or,if possible, try a small area to get a better idea.Alkyd or acrylic enamels can be poured back intothe can in a pinch but activated paint and acrylicsmixed with hardener are history in a relativelyshort time after they are mixed.

Also, some of the newer alkyd enamels,which use the latest low-VOC formulations,especially if they have been thinned for spraying,can cause problems such as seeding when theyare poured back into the can. Given the choice ofsaving a few dollars worth of leftover paint alongwith the possibility of contaminating a wholegallon of paint or throwing away the few bucksworth of paint remaining in the gun, I choose thelatter.

Another thing to bear in mind is that, shouldyou run out of paint on a large, flat surface, bythe time you mix up some new paint, the paintwill have dried on the surface and the new paintwon't blend. Consequently, you should try tomix an amount of paint that will take you to theedge of a panel, molding or some other logicalstopping place (either that or stop, before thepaint runs out, at a good spot).

There are two measuring devices that youwill find very handy for mixing activated paints:soup ladles; and coffee cans. Soup ladles comein a handy 8 oz. size and can be used to scooppaint out of the can without making a mess.They are cheap and the chrome plating cleans upeasily with solvent. Coffee cans are plentiful(especially if you co-habitate with a coffeeaddict, as I do) and they have the added benefitof coming with a resealable lid. Calibrate a fewahead of time with a kitchen measuring cup andtap water. A small dent (visible on the inside ofthe can) should be made at the 8, 16, 24, and 32oz. marks with a screwdriver blade, nail, etc.(being careful to dent only, not punch through) orthe natural rings stamped in the can may beemployed.

Mix up the paint in the correct proportions (Icould tell all sorts of funny stories about this so

16 1998 January

make sure you get it right – apparently, its easynot to). If it needs an induction period (i.e. timeto contemplate the meaning of being paint beforeit is applied), mix it ahead of time and let it standas required. For big jobs, having one person tospray and one to mix, etc. is a definite plus.

Reducers (painter’s jargon for thinner) are:mineral spirits (Stoddard solvent); VM&PNaptha; toluene; xylene; ethyl acetate; butylacetate; acetone; and methyl ethyl ketone(MEK). Various blends of any or all of thesesolvents in combination with retarders,accelerators and leveling agents are used toreduce the viscosity of the paint to a sprayableconsistency, accommodate climatic conditions(e.g. temperature and humidity), facilitateleveling, speed drying, etc. In general, thesmaller the molecular size of the resin (resin sizeis usually inversely proportional to the solidscontent), the less reducer required. Following theadvice of the paint manufacturer with respect toreduction is wise unless you are familiar with thefinish being sprayed.

If a reducer is necessary, add it in smallamounts until the desired consistency forspraying is reached. Most paints come with atime marked on the can (e.g. 15 seconds in a #2Zahn cup), that indicates the ideal sprayingviscosity. So what the heck does that mean,anyway? Simple! A Zahn cup is a little cup witha fixed volume and a carefully sized orificedrilled in the bottom. You fill it with paint andtime how long it takes the paint to run out of thehole. When it matches the time given (in ourexample, 15 seconds), the viscosity is correct forspraying. In the software business, we call this akludge – in the paint business, its called a Zahn.Another name for this kludge, in the paintbusiness, is a #4 Ford viscosity cup – same idea.

Anyway, the pros just eyeball it or time howlong it takes for the paint to stop dripping off ofthe end of a stir stick (say four seconds). If itruns pretty good, it will probably spray prettygood (actually, most anything will spray, its justa question of how will it level out or run and sagand how good it will look when you’re done).

You can spend plenty of dough buying theapproved reducer with the paint manufacturer’sname on the can or you can try my favorites:MEK (methyl ethyl ketone) for epoxy andVM&P (Varnish Maker’s and Painter’s) Napthaor mineral spirits for alkyd enamel.

Polyurethane, having roughly the same viscosityas water, needs no improvement nor do some ofthe newer alkyd formulations which aresprayable right out of the can or with the additionof a small quantity of mineral spirits.

One other thing: unless your name is SpeedyGonzales, you can probably skip adding anyaccelerator to your paint. The pot life is usuallyshort enough as it is and the accelerator will onlymake it shorter. If being assured of an adequatedrying time is not possible (or if you are paintingthe day before a charter) you may wish to use itbut, otherwise, I wouldn’t.

Paint Application

Begin spraying by testing the flow rate,spray pattern, etc. on a piece of scrap orsomeplace hidden. I make a note of my paintgun settings for each kind of paint, as I becomefamiliar with the gun. That way, I can load thegun with paint, dial up the numbers and beginblasting with a minimum amount of fine tuning.

You should hold the gun about eight to teninches from the surface to be painted and at rightangles to it. Start off of the surface, if possibleand trigger the gun to start the paint flowing (anyspattering will not mar the surface). Move thegun in a straight line, holding it perpendicular tothe surface and moving it at about one foot persecond. Avoid sweeping the gun in an arc as thiswill result in an uneven application of the paint atthe ends and center of the arc. Continue yourpass right off of the end of the panel beforereleasing the trigger. Start the next pass so that itoverlaps the first pass by half and continue in thismanner.

The paint should go on with the edge of eachstripe having a dry appearance and the center ofeach stripe appearing slightly wet or shinylooking (this is called a medium wet coat). If itgoes on wet, the paint will level and look good.If the paint goes on too dry, the surface willacquire a dry textured look like fine sandpaper.If the paint is too thick or has lousy levelingproperties it will orange-peel (the surface of thepaint will look bumpy like the surface of anorange).

There is a fine line between too thick and toothin, too heavy and to light when spraying paint.If the paint is too thick, it will not level properly.If it is too thin, it will run and sag. Similarly, if

1998 January 17

the paint is applied too heavily, it will sag,curtain (long lines of sagging paint caused by thepaint running down in a united front, like a wave)or run. And, if the paint is applied too lightly, itwon’t hide and may telegraph unwanted detailsuch as surface imperfections. If you do haveproblems, resist the temptation to fix them whenthey happen – they’ll only get worse. Rather, fixthem up later when the paint has cured (its not ashard as it sounds).

Other problems that can occur from layingdown the paint improperly include failure toprotect the underlying surface (dry film thicknesstoo thin) and pores in epoxy (epoxy outgassesslightly when curing. If the paint is applied tooheavily, the outgassing will cause a tiny bubbleto form. When the bubble bursts, a pore is leftbehind that can allow water and air to penetratethe film). Effects such as fish-eye (a circular,eye-like appearance to the painted surface) areusually caused by surface contamination(especially by contaminants containing silicone).Orange-peel can be caused by surfacecontamination as well as poor leveling.

The proper approach to use when spraypainting is to lay down several thin coats of paint,one on top of the other, with a short drying timein between (if it isn’t practical to allow only ashort drying time in between, scuff sand betweencoats that have cured for longer than 72 hours).Each coat should go on slightly wet or shinylooking. The last coat may go on a little wetterthan its predecessors because it has something tostick to. This approach works much better thantrying to apply the paint as a single, thick coat inone pass.

Most paint guns spray in a fan-shapedpattern (although my HVLP gun will alsoproduce a circle). The motion to use whenspraying, with this kind of spray pattern, is backand forth or up and down in a series of partiallyoverlapping stripes. The air cap can usually berotated so that the fan is at right angles to thedirection of motion (having the fan set at 90degrees to the direction of travel will lay down awide stripe) while the gun handle is aligned withyou hand so that it can be held at a comfortableangle.

Start painting the spot that is farthest awayor hardest to reach (you want to work towardyourself so that you never have to lean on or over

the freshly painted area). To reiterate, if you arepainting flat or gently curved surfaces, move thegun along in a straight line at an even pace whileholding it equidistant from the surface beingpainted at all times (think about what will happenif the motion is jerky or if you pull the gun awayfrom the surface as you go – the paint is sprayingout at a constant rate and it will either build up orget too thin). Do not swing the gun in an arcwith it far away from the surface at the beginningand end of the arc and up close in the middle. Ifat all possible, begin and end each spray pass offof the surface being painted. As you make eachstripe, overlap the previous stripe by 50 percent.

You can work on any area that iscommensurate with your reach. Try to moveyour whole body as you go back and forth in asmooth, flowing motion. If you want to ensureeven coverage, lay down two sets of lighterstripes at right angles to each other. Connecteach area to the next before it dries too much oryou will have a problem with leveling andmisting that can be visible in the paint after itdries. If you must stop (e.g. to refill the paintpot), try to do so at a natural break such as anedge, window frame, seam, molding, etc. whereit won’t be obvious to the eye. Smallimperfections due to misting can be rubbed outwith rubbing compound later on, if absolutelynecessary.

If you are painting oddly-or irregularly-shaped parts (e.g. undercar components), try toaim the gun at each part from several differentangles. Remember, the air (and the paint it iscarrying) doesn’t go around corners – it onlygoes one direction (i.e. straight-in) – unless youare using an electrostatic rig. Also rememberthat, if you can’t see it, it probably doesn’t haveany paint on it.

You will usually start out by applying one ortwo coats of primer and possibly a coat ofsurfacer, followed by one or two finish coats.For primer, if two coats are being used, I like toapply a contrasting color with each coat. In thisway, I will notice any holidays (a spot notreceiving any paint) and, hopefully, correct them.

The finish prime coat should end up being alight color (gray is frequently the choice ofdiscerning painters). Once the primer has cured,study the surface carefully under glancing light.Either wait until the sun is shining at an oblique

18 1998 January

angle so that it glances off the roof or car sides orshine a strong light parallel to the surface ofwalls, etc.

The combination of the strong light, lowillumination angle and the light color of theprimer will cause any surface imperfections to behighlighted by shadows so that they stand out.Each imperfection can be circled by a pencil sothat it will be visible later on when it comes timefor final repairs.

The inevitable small nick can be filled withautomotive spot and glaze putty. This product isformulated for application over primer and itneeds no priming afterwards so it can be used forfixing small areas without requiring repainting.Major divots must be filled with Bondo, sandedout and re-primed.

Once all of the imperfections are repaired,the surfacer, if any, is applied. If you chose aprimer that can be sanded or if you aren’t lookingfor a mirror-like finish (or you are just tired ofsanding), skip this step. Otherwise, apply theproper surfacer for your chosen paint system,hopefully in a contrasting color and allow it tocure for a few days.

Now, the final sanding should be done. Fora surface as smooth as the proverbial baby’sbum, you can’t beat wet sanding, preferably with320 grit silicon carbide wet or dry paper. Whensanding with this paper keep it well flooded withwater. The water will float away the materialremoved and prevent the paper from clogging(clogged paper can cause scratches as well aswearing out very quickly). Remember that youare not trying to remove too much material. Justsmooth things out. The surface is smooth whenit appears uniformly dull.

Applying the final coat or coats of paint isjust like applying the primer coat or coats. Workon areas that are easy to reach, don’t overreachfresh paint, hold the gun level and lay downoverlapping stripes so that the paint looks wet. Ifyou are using polyurethane, don’t let it spookyou. To me, it sprays pretty much like any otherenamel or epoxy.

Striping

Striping can be applied in two ways: paintedon; or taped on. Wide bands are usually paintedon while narrower bands or reflective stripes are

taped on. If you have the time and the patienceto mask and spray narrow stripes, there is noreason not to paint them on, however.

Products such as Scotchcal and Scotchlitecan be used for striping that appears clean andcrisp and is easy to apply. This kind of striping ispreferred for separating wider color bands, alongthe edges of side sheets and belt rails oranywhere that a reflective, safety stripe isdesired. Essentially, these products are apolyester tape, available in a wide variety ofwidths and colors, that is applied much like anyother adhesive tape. Once it is applied, theadhesive laminates the tape onto the paint toform a strong, unbreakable bond.

If you are spraying on color bands or stripes,plan the painting sequence so that you paint thelighter colors first. Spray the underlying color sothat it extends six inches past the boundarybetween the two colors (e.g. for a six inch stripe,spray approximately 18 inches) and so that thecoat of paint tapers off in thickness to thesurface. The idea is to avoid any sudden changesin thickness that will telegraph through theoverlapping color. You may even wish to sandthe first color nearly up to the boundary tofeather it out.

Apply the masking using a good qualitystriping tape like 3M FineLine plastic tape andmasking paper, if necessary. Make sure that allof the edges are pressed firmly into the surface sothat the paint will not bleed under the tape bycapillary action and leave a ragged edge.

Once you have sprayed the paint, allow it tocure for the amount of time specified by themanufacturer and then remove the maskingpromptly. Pull the tape off carefully by doublingit back, flat on itself and pulling away from thepaint at 45 degree angle. This will ensure thatthe tape peels cleanly away and doesn't removeany fresh paint.

Lettering

Lettering, like striping, can be applied byeither painting it on or by using adhesive filmssuch as Scotchcal or Scotchlite (described in thearticle, “Lettering Railway Equipment”). If youhave the time and patience to cut and applystencils, painted on lettering is the way that itwas done in the past. Most lettering, however, isdone with adhesive film nowadays because the

1998 January 19

time to apply lettering film is much shorter thanthe time required to paint on lettering and theresults are just as good or better.

Should you wish to paint on lettering, thefirst step is to have a stencil cut or to cut oneyourself. Many places that paint signs,billboards, etc. can either cut stencils or directyou to someplace that does. If you elect to cutyour own stencils, you will need a large, clear,flat area where you can lay out the stencil filmand cut it.

Lettering patterns are pretty easy to generate,especially if you have a computer and a laserprinter. There are literally hundreds of fontsavailable and you can pick one that you like orthat matches what you need. Havingenlargements made of these letters will give youany special patterns that you require. Otherwise,many common patterns are available from theplaces that cut stencils. Much of the period carlettering was done with the famous RailroadRoman font which is a classic serif font that isclose to Times Roman (and everybody hasTimes Roman).

Sheet products are now all cut by a machinethat features a computer-driven cutter thatfollows an outline of the chosen font. As aresult, the selection of fonts available is huge(font libraries often have upwards of 600 fonts).On top of this, practically anything that can bedigitized can be used to generate an outline thatwill drive the sheet film cutter.

After you receive your cut stencil, carefullyapply it to the car side using layout linesmeasured from the edge of the side sheet, beltrail, etc. Use something that won’t permanentlymark the paint, such as a soft pencil, watersoluble marker or registration marks made withsmall pieces of tape.

Stencils are applied in the same manner aslettering film, by removing the backing paper andcarefully pressing the stencil film in placeaccording to the layout marks. Be sure to rubdown all of the edges to ensure proper adhesionand eliminate bleeding of the paint under thestencil. Mask around the stencil with maskingpaper, if you anticipate overspray problems.

Spray the paint at the stencil just as youwould normally spray the surface that it isapplied to. Start off of the cut-out area and

stroke the gun in stripes, as usual, ending up offof the cut-out area. Paint the entire stencil in thismanner, overlapping each stripe, the same asalways.

When the paint has dried the requisite lengthof time, the stencil should be carefully removed,exercising caution so as not to peel off any freshpaint with the stencil. A sharp knife may beuseful in cutting just through the paint so that thestencil pulls away cleanly from any problemspots.

Finishing Touches

Once the final coat of paint is applied, thereare a few things that can be done to enhance yourpaint job and keep it looking great.

Satin-finish surfaces, such as those found incar interiors, can be kept clean by washing withwarm water and a mild detergent. Theoccasional scratch or chip can be touched up witha small artist's paint brush without appearing toobad. Besides keeping the paint clean and touchedup, nothing much else needs or should be done toit.

Glossy-finish surfaces need slightly morework to keep them looking great. Smallimperfections, including misty areas caused byoverspray from adjacent panels, can be rubbedout using an automotive rubbing compound,available from your paint supplier (see Table 6for information about the ubiquitous Meguiar’srubbing compounds). Rubbing compound isessentially a very fine abrasive suspended in alubricant so it removes paint as you rub. Go easyand don’t rub through the paint or you’ll be verysorry.

Outside paint should be given an initial coatof wax (after it cures for a few months) and thenmaintained by a periodic application of wax (sayonce a year). A good quality automotive waxshould be used and then buffed out (a poweredbuffer may help) with a soft cloth.

Any small rock chips (I know it is sad tothink about this subject but it is inevitable) can becleaned out and touched up with an artist’s brushor may be feathered out and re-sprayed, followedby rubbing. Polyurethane is, unfortunately,difficult to fix but enamel responds well to thistreatment. In either case, bare metal should becovered up before it has a chance to start rusting

20 1998 January

and before the rust can work its way under thepaint film, causing it to lift.

If the car gets dirty, it can be washed toremove the dirt. Be sure to wash first with

detergent and lots of water to loosen the dirt andfloat it away. To loosen the dirt, use a soft rag orbrush and lots of water. Dirt bears a remarkablesimilarity to the grit in sandpaper so you canimagine what pushing it around and around, overyour paint, will do. Follow up with lots of rinsewater to flush away the dirt and detergent [Hey,how many times did he say lots of water,anyway].

Other than following these few simplemaintenance steps, your paint, if properlyapplied, should look good and keep looking good

for 10 to 15 years. And, you’ll look great inthose publicity photos, standing next to yourcatchy paint job, for years to come.

Appendix A – Sand-Blasting Equipment

When tackling a restoration project the sizeof a railway car, owning your own sand-blastingequipment is almost mandatory. There arehundreds of opportunities for using a sand-blasterto clean up parts, remove rust and old paint andso on. Making an investment in some goodquality sand-blasting equipment is well worth it.

Sand-blasting equipment can be divided intotwo categories: pressure feed; and siphon feed.The former type usually is sold as good industrialand professional equipment while the latter typeis sold as the cheap, backyard, do-it-yourselfsand-blasters. The exception to this rule is inmost sand-blast cabinets which are frequentlysiphon feed, primarily for the purposes ofcontinuously recycling the blasting media.Although, siphon blasters work, they are muchslower and less aggressive than pressure blasters.For my money, there is no reason to mess aroundwith siphon blasters when doing big jobs such aslarge castings, your center-sill, etc. For smalljobs and in a blast cabinet, a siphon blaster is OKbut even some blast cabinets make a provisionfor you to use a pressure blaster.

Sand-blasting works by propelling sand (orsome other abrasive) against the surface to becleaned by a high-pressure jet of compressed air.The impact of each particle knocks looseanything that isn’t firmly affixed to the surface(e.g. rust, loose paint, bird-shit, etc.) Because theparticles are tiny, they can get into every nookand cranny and remove all of the extraneousmaterial. The cleaning action of each individualparticle is small but the cumulative result of aconstant stream of them is large. Observing asand-blaster in action is almost a miraculoussight.

Item # Description

M-0216

#2

Fine-Cut Cleaner

Removes stubborn paint defects such as lightoxidation, swirls, scratches and hard waterspots.

M-0116

#1

Medium-Cut Cleaner

Quickly removes swirls, water spots andwater sanding marks.

M-0416

#4

Heavy-Cut Cleaner

Removes serious paint defects. Removesdeep swirl marks, scratches and severeoxidation as well as etching from acid rain.

M-8432 Compound Power Cleaner

Fastest, most aggressive cutting poweravailable for rapid removal of deep paintdefects and sanding marks.

C-2000 Compound Power Cleaner

Gently wipe away overspray, bug debris,water spots, oil and grease and other surfacecontamination.

M-0316

#3

Machine Glaze

The ultimate machine-applied shine.Revitalizes paint. Residue wipes off easily.

M-0916

#9

Swirl Remover

Cleaner and polish in one. Eliminates swirlmarks, tiny scratches and mild defects.

Table 6: Meguiar’s Compounds and Polishes

1998 January 21

The concept is pretty simple so how do youput it into action? In a siphon blaster, the airfrom the compressor is fed through a nozzlewhich is drilled with a small orifice. Ahead ofthe orifice is a siphon tube set at right angles tothe air passage (see Figure A1). As the air passesthe siphon tube a vacuum is created. A hoseattached to the siphon tube is attached to agravity-feed hopper filled with sand. Thevacuum at the other end of the hose causes sandto be sucked up the hose to the nozzle where it isentrained by the passing air and propelled out theorifice towards the part being sand-blasted.

A pressure-feed sand-blaster uses positivepressure on the sand to feed it to the nozzle. Thesand reservoir is a pressure vessel that is filledwith sand and then closed. When it ispressurized with air the sand is pushed out of thesand reservoir and mixed with more air. Thewhole mess, sand and air, accelerates down thesand hose to the nozzle where an orifice forms itinto a jet and aims it at the piece being blasted.Because the sand has longer to accelerate, ittends to be form a more energetic stream and,hence, be more efficient at cleaning than thestream of sand from a siphon-blaster.

Both kinds of sand-blasters use a nozzle toform the sand stream into a high pressure jet.The nozzle, as you might imagine, exposed as itis to a constant stream of abrasive, is subject to ahigh rate of wear. Typical nozzle materials arecarbon steel, ceramic and tungsten carbide.Typical nozzle lifetimes are one hour for steel, 3-5 hours for ceramic and 60-100 hours for carbide.The prices vary correspondingly but, when all

things are considered, carbide, although pricey, isthe best deal and steel, although cheapest, ispretty much pointless.

Although it is frequently called sand-blasting, other kinds of abrasive are often used.Table A1 shows some of the more commonalong with their suggested uses. Whatever

blasting media you use, it should be clean andvery dry and you should strain it through ascreen, to prevent clogging ,before every use.

Sand-blasters are known to be air hogs and itis not hard to see why. A sand-blaster isbasically an open pipe connected to your aircompressor. The amount of air used isdetermined mainly by the amount of friction inthe nozzle. Consequently, one of the things toconsider carefully when setting up a sand-blasteris compressor selection.

Figure A1: Siphon Blaster

Media Description/Uses

GlassBeads

Several sizes available (60-80 isgood).

Produces a satin finish on brass,aluminum and other soft metals.Removes rust and scale. Creates littledust.

CrushedGlass

40-80 mesh is typical.

Sharp edges cut fast. Coarser finish,moderate dust.

SiliconCarbide

80 mesh is typical.

Highest quality abrasive. Stays sharpand lasts longer. Cuts fast.Significant dust. Excellent for etchingglass.

AluminumOxide

Several sizes available (50 is good).

Leaves a smooth, textured finish.Cuts fast. Significant dust. Longlasting.

WalnutShells

35-60 mesh is typical.

Slow rust/paint removal. Verysmooth finish. Will not pit or damagechrome. Can be used on wood withcare.

Plastic 30-40 mesh is typical.

The latest technology. Used to stripairplanes. Perfect for stripping paintand oxidation from aluminum. Willnot etch or scratch aluminum orchrome. No dust.

Table A1: Blasting Media

22 1998 January

The smallest pressure-feed sand-blaster willlikely require a three horsepower (this is realhorsepower, not fake or developed horsepowerlike many home/hobby compressormanufacturers like to quote) compressor,although five is better. The smallest siphon-feedsand-blaster will likely require a five horsepowercompressor. Don’t skimp on the compressor.You won’t be running the sand-blasterintermittently (trust me) and an underpoweredcompressor won’t keep up.

The air supplied should be clean and dry. Iuse a moisture filter right at the sand-blaster. Afairly long air line (50-100 ft. of hose or 25 ft. ofcopper pipe) will ensure that the air has a chanceto cool down and that the moisture can condenseout and be caught by the moisture filter. If theair is not dry, you will experience problems withclogging that will drive you crazy. Similarly, toprevent clogging, the blasting media must also beclean and dry.

Finally, a few words on safety. Don’t aimthe sand stream at yourself or anyone else (wearrubber blasting gloves, if you’ll be handling partswhile blasting). Wear a blasting hood to keepflying sand out of your face and eyes and makesure there’s plenty of fresh air available (or weara respirator, preferably supplied-air). Avoidbreathing silica dust, as it irritates the mucousmembranes and lungs severely.

Appendix B – Sandpapers

Sandpaper belongs to a family of abrasivesmore properly known as coated abrasives. Thisfamily of products consists of a thin layer ofabrasive grains bonded to a substrate such aspaper or cloth. Within the family, coatedabrasives come in a variety of forms such assheets, disks, rolls or belts. The commonestabrasive grains used in the manufacture of thisfamily of abrasives are aluminum oxide, siliconcarbide, garnet and sometimes aluminazirconium (see Table B1).

There are four major types of backingmaterials employed in manufacturing coatedabrasives: cloth; paper; fiber; and combination.Also, a variety of other substrates such as nylonfiber and screens can be coated with abrasive forspecial applications.

The most common cloth backing is cotton.Polyester cloth backing is waterproof and

provides high strength and resistance to tearingor edge wear. The adhesive film that is used onthe backing has a significant effect on itsflexibility. Cloth is identified by weight andflexibility. “J” weight is a light, highly flexiblematerial while “X” weight is a heavy cottonbacking that can be coated in a full range ofabrasive grades.

Paper is identified by weight and flexibilitytoo. The lightest weight paper, “A” weight, is

used for fine and medium grades of abrasive.“C” and “D” are intermediate weight papers thatcan be coated with the medium and coarse gradesof abrasives.

Fiber backing is a very tough, vulcanizedmaterial made from rag stock and used primarilyas a backing for abrasive disks.

Combination backing is composed of paperand cloth laminated together and is,consequently, very sturdy and shock resistant.Combination backing is typically used to back upthe coarse grits found in floor sanding productsand, so, will not concern us.

Abrasive Grain Description

AluminumOxide

A tough, blocky-shaped abrasivegenerally used for sandingmetals and other high tensilestrength materials.

Silicon Carbide A very hard, very sharp abrasiveparticularly suited to non-metallic materials such asconcrete and for wet-sandingpaint.

Garnet A natural, brittle, red, silicatematerial, of medium hardness,which tends to fracture in usecreating new cutting edges.Used for sanding wood

AluminaZirconium

A fused abrasive that is verydense with a very fine crystalsize. It is crushed to produce asharp-edged, blocky shape. Usefor sanding ferrous metals,stainless, high tensile steel andwelds where heavy duty sandingand a high level of materialremoval is required. Exhibitsextremely long life.

Table B1: Coated Abrasive Grains

1998 January 23

There are three major types of bondtechniques used in coated abrasives: glue overglue; resin over glue; and resin over resin. All ofthese bond types are two-layer processes used toanchor and lock the abrasive to the backing.Different applications determine which type ofbond should be used. Resin over glue makes abond very resistant to heat. Resin over resin is avery strong bond not susceptible to heat andmoisture.

All coated abrasives are stiff and rigid afterthe curing of the bond. To achieve the flexibilityrequired for the application, a mechanical flexingprocess is used during manufacturing. Thisprocess is actually a controlled cracking of thebond in one or more directions to achieve thedesired flexibility.

The stiffness and smoothness of the backingand the hardness of the grit all influence thespeed and quality of the cut of coated abrasives.A soft grit on a smooth, pliable backing will cutslowly but produce a smooth surface. The otherextreme, a hard grit on a rough (e.g. cloth), hardbacking will cut like lightning but leave a lowerquality finish. Generally, the manufacturer of theabrasive will select a backing material thataugments the grit and helps it to do its intendedjob. You can control this to a certain extent byexchanging the backing pad on the sander beingused: hard equals a more aggressive cut; softequals a smoother finish.

The terms open and closed coat refer to thespacing between the abrasive grains on thesubstrate. Closed coat means that the grains areadjacent to one another with no space in between.Open coat means that the grains are set apartfrom one another with typical surface coveragesapproaching 60%.

The majority of applications will benefitfrom closed coat sandpaper because of thequantity of abrasive that is brought to bear on thework. In situations where loading is likely (e.g.soft, non-ferrous materials, painted surfaces,etc.), open coat sandpaper will resist cloggingand extend the abrasive’s useful life.

As additional insurance against clogging,some sandpapers are available with a stearatecoating. Stearate is essentially soap and itprevents the material that is removed from thesurface being sanded from sticking to thesandpaper. Stearate paper is not for every

application (e.g. it cannot be used to wet sand)but it does work well on body filler, paint,fiberglass and aluminum. Be aware, however,that you may need to clean the surfacescrupulously before painting to remove any soapthat is left behind.

If you consider sanding on a microscopicscale, those grains of abrasive are actuallycreating a series of gouges or grooves that runparallel to the direction of sanding. The actiondesired, when sanding, is for each sanding pass toremove the gouges left by the previous grit. Thisis accomplished by starting with a coarse grit(80-100) and moving up, a size at a time, untilyou reach the grit that will give you the desiredfinish smoothness (150).

You should move up from the lower-numbered grits to the higher-numbered grits inprogression (i.e. 80, 100, 120, 150) to keep yoursanding time to a minimum and extend the life ofthe sandpaper. Although this may seemcounterintuitive, it isn't. If you keep in mind thateach succeeding grit is removing the scratchesleft by its predecessor, it should be more apparentthat when you skip a grit size, the finer abrasivehas to work harder to remove the significantlylarger scratches and is more prone to wear out, aswell as taking much longer to do the job.Skipping a grit size may actually double thesanding time, although, on soft surfaces such asaluminum, it may prove to be an effectivetechnique for speeding things up.

Appendix C – Gloves

A good pair of gloves should be used whenhandling paints and chemical strippers becausethe compounds found in them may be toxicand/or caustic – many of the organic chemicalsused in paint can be absorbed through or irritatethe skin and caustic strippers can severely burnthe skin. Gloves are excellent protection againstmishap.

It is important to use the proper kind ofgloves for the chemicals being handled (seeTable C1). Unfortunately, one type of glovematerial is not protection against everything.Rather, a couple or three different kinds ofgloves should be procured so that you’ll alwayshave the right ones available. Also, considerbuying a few pairs of each kind of glove becauseit is easy to tear them (when I tear a glove, I setaside the matching one that is still good, on the

24 1998 January

off chance that the next time I tear a glove it willbe the other one). My two favorite gloves arenitrile for painting and butyl for stripping withmethylene chloride type strippers. I useneoprene when working with oils, solvents, tarsand caustic strippers and also for painting.

Before you don a pair of gloves, inspectthem for wear and tear. Hold each glove in yourhand and blow it up like a balloon. Squeeze thecuff shut and press on it with your other hand. Ifthere is a tear, the glove will deflate through it.If the glove is intact, it will prove hard to deflate.

Discard any torn gloves.

Keep your gloves clean by wiping them offwith solvent as you clean up your equipment.This will prolong their life and keep them fromtransferring paint or chemicals to anything thatyou inadvertently touch. When you remove yourgloves, turn them inside out and hang them up toallow accumulated perspiration to dry out. Oncethey are dry, reverse them and store them out ofbright light, flat and in pairs, ready for their nextuse.

Appendix D – Respirators

There are two types of respirator that can beused when applying paint: the organic vaporrespirator; and the supplied-air respirator.Furthermore, when scraping lead paint and/or

sandblasting, you should wear a HEPA orsupplied-air respirator.

Organic vapor respirators consist of a pliablerubber face mask with straps to hold it in placeand a set of replaceable filters that screw into it.There are usually four rubber flapper valves (thinrubber discs that seat on a ring set into the facemask), two for inlet and two for outlet. As youbreath, air is drawn through the cartridges via theinlet valves. Exhaled air exits through the outletvalves.

The cartridges contain activated carbon

which has a strong affinity for organic molecules.As the air passes over the carbon, solvent (whichis an organic molecule) is extracted from the airand it is purified. When the activated carbon isspent (you will start to smell paint), thecartridges are thrown away and replaced. Notethat the activated carbon cartridge only works onorganic vapors. Paint mist (i.e. small droplets ofpaint) is frequently removed by a felt-like pre-filter which can be changed often to prolong thelife of the organic filter.

Tiny particulates such as asbestos fibers,lead paint dust and silica (sand) are best removedby a HEPA (High Efficiency Particle Arresting)filter, since the organic vapor filter is prettyineffective at this job. The HEPA cartridgesusually screw into the same face mask as theorganic vapor cartridges so one face mask may

Chemical Tested Butyl Neoprene Nitrile PVC Latex

Acetone >480 9 ∅ ∅ 10

Methanol ∅ 103 11 45 20

Methyl Ethyl Ketone >480 22 ∅ ∅ 5

Methylene Chloride 24 6 ∅ ∅ ∅

Mineral Spirits ∅ 127 ∞ 150 ∅

Phosphoric Acid ∅ >480 >480 ∞ ∅

Sodium Hydroxide ∅ >480 ∞ ∞ ∞

Toluene 21 4 10 ∅ ∅

Xylene, Xylol ∅ 23 75 ∅ ∅

Table C1: Glove Material Chemical Resistance(Time in minutes to break through glove. Use not recommended if marked ∅.)

1998 January 25

be made to do dual duty. In some cases, twofilters may be ganged up to protect againstparticles and organic vapors as in the case whereyou are removing lead paint with a methylenechloride stripper.

A supplied-air respirator consists of a rubberfacemask, much the same as the facemask usedwith organic vapor/HEPA respirators, possibly apressure reducing regulator, a supply line and anair source (compressor or turbine).

The premise behind a supplied-air regulatoris that the air source is located in a remotelocation where the air is guaranteed to be clean.The air is compressed and sent to the face mask,via the supply line, where you get to breath it.

Some supplied-air respirators use a turbinewhich generates a high volume of air under lowpressure. These have a large diameter hose(which, incidentally, must be of a certain lengthto cool the air that was heated by the turbine andrender it breathable) and the air is breatheddirectly. Others use a pressure reducingregulator to accept typical high-pressure air (e.g.90 p.s.i.) and reduce it to low pressure at highvolume for breathing. These must be suppliedwith clean, oil-free air through a regular air hose.A small oil-less compressor of 1 to 1-1/2 HPworks well and can be remotely situated.

The benefits of supplied-air respirators arethat the respirator is always pressurized. If theface mask leaks, the leak is out, not in. Youwon’t be breathing solvents or anything otherthan fresh air and for paints such as polyurethanethis is imperative. The benefits of a full-facerespirator is that your eyes won’t be collectingpaint while you are spraying (by the way, thechemicals in polyurethane paint can be absorbedthrough and/or irritate the skin of the face andeyes) but this is more your own personal choice.Especially if you wear eyeglasses, a full-facerespirator can be difficult to fit. Perhaps a partialface mask and goggles may be more to yourliking.

Organic vapor/HEPA respirators areacceptable, where appropriate, in most cases,provided that they fit well. Achieving a goodseal between your face and the mask is mostimportant and, if you are among those of us whosport a beard, this may be difficult. Therespirator should be adjusted so that it fits snugly,and then the seal should be tested by covering the

exhaust vent with your hand and blowing out. Agood seal will result in the respirator inflatingand you should experience difficulty in blowing.If you can’t get a good seal, Vaseline can be usedto help (especially with beards) but you mayneed to switch to supplied-air.

Supplied-air is not the answer for everyone,it being much more expensive as well ascumbersome and not acceptable in situationswhere quick egress in the event of air supplyfailure is impossible. However, if you do decideto use a supplied-air respirator, a goodintermediate cost solution (e.g. I paid about $500for a facemask, air hoses, and compressor – nottoo much to pay for a life insurance policy on mymeasly life) can be had that will do the job inmany cases where an organic vapor/HEPArespirator won’t.

The set up that I use is a small, oil-lesspancake compressor located a couple hundredfeet from the spraying area. The air hoses fromthe compressor should be 3/8" I.D. and shouldhave Schrader-type connectors (so that theywon't pop apart when they become snagged onsomething). The mask, which I purchased from asurplus store for $150, is a full face mask. Fullface masks protect your eyes as well as yourlungs. To be used with this setup, the mask mustcome with a pressure demand regulator to dropthe high pressure air from the compressor to afew pounds and convert the air flow to highvolume.

Appendix E – Paint Spraying Equipment

Probably more so than in any otherapplication, except for large industrial plants andcommercial airplanes, the spray equipment thatwe use to paint railway equipment is of primeimportance. The reason is cost! When youconsider the price of the paint (e.g. $100-200 pergallon) and the large areas to be painted (e.g. 800square feet for a car side), you want to be realsure that the paint goes onto the car and not ontoyour neighbor’s laundry, drying on theclothesline.

To me, cost, rather than any other reason, iswhy I use HVLP spray equipment. However,there is also the release of VOCs into theatmosphere to think about. The EPA is passingrules about paint formulations that are meant toreduce VOCs and they are also becoming

26 1998 January

involved in the area of paint application. So, ifcost isn’t enough to convince you, maybeenvironmental regulations are. Personally, Iwouldn’t bother with anything other than HVLPequipment.

Well, what is HVLP equipment, anyway? Alittle history, first. Conventional spray guns usedcompressed air to force paint out of the nozzle ofthe gun where it met with a blast of high-pressureair directed at it by an air cap (see Figure E1).The turbulence of the air stream caused the paintto be broken up into a cloud of tiny droplets in aprocess known as atomization. Then, the airfrom the air cap shaped the cloud of paint into a

fan and propelled it towards the surface beingpainted.

The atomized paint droplets impinged on thesurface with a significant amount of energywhich caused them to stick and level out in auniform coat. Mostly. The higher the gun airpressure, the finer the atomization and thesmoother the resulting finish but with one caveat.The high energy imparted to the paint dropletscaused them to misbehave badly. Some of themhad so much energy that they would bounce rightoff the surface. Others were literally blown rightby the surface. The net result: 30% of the painton the surface and 70% airborne.

Time to rethink the equipment! Why not useair at a lower pressure to move the paint so that,when it strikes the surface, it sticks instead ofbouncing around? To make up for the lower

pressure, use lots of air. This way, the paint goeswhere it was intended to go, not on Mrs.O’Grady’s laundry. Voila! HVLP (HighVolume, Low Pressure), with typical transferefficiencies in the 70% range, was born (for moreinformation about how to keep the paint frommissing the mark altogether, check outelectrostatic systems at your painting equipmentdealer).

But, how to produce the high volume, lowpressure air? There are two ways. The first is totake low volume, high pressure air (e.g. from acompressor) and allow it to expand to a muchlarger volume at a lower pressure. This is the

idea behind a conversion gun. The second is togenerate lots of low pressure air in the first place.This is the idea behind a turbine gun.

If you have existing spray paintingequipment (i.e. a compressor), you will probablywant to buy a conversion gun. Another thing toconsider is that, while HVLP by definition is anygun that produces 10 p.s.i. or less of air pressure,conversion guns are closer to 10 p.s.i. whileturbine guns are in the 3-5 p.s.i. range. As wasmentioned before, the higher the air pressure, thebetter the paint atomization and the smoother thefinish. Consequently, conversion guns tend toproduce a better finish. On the downside,conversion guns are notorious air hogs (although,the Fuji venturi gun will, when available, be animprovement) so at least a 3-5 HP compressor ismandatory.

Figure E1: Air Caps

1998 January 27

A turbine gun uses the same kind of turbinethat is used in a vacuum cleaner (as a matter offact, I have a homemade turbine unit that I builtfrom a vacuum cleaner motor – works great),running as a blower instead of as a vacuumgenerator. Most of the good turbine units aretwo- or three-stage (i.e. the blower has two orthree impellers that step up the pressure) and theyproduce 3-5 p.s.i. at 80-100 c.f.m. A unit of thistype is a small, light box that can go anywhereand plug into a 120V outlet.

So, how to choose which kind of HVLP gunto buy. If you already have a compressor and arethinking of painting your car's exterior, aconversion gun is probably the way to go. Agood one such as the Devilbis or Lex-Aire (mypersonal favorite) is $300-400. If you want asmall, light, portable unit that produces a veryacceptable finish, say to do car interiors, aturbine unit is just the ticket. A good one such asthe Apollo, Graco/Croix or Fuji is $500-600(including the turbine) or, if you just want topurchase the gun for your homemade unit, its$250. Given the workout that this gun can expectto be put through, don't scrimp on the amount ofmoney that you spend. Buy a top-quality gunand you won't regret it.

Appendix F – Useful Sources of Information

The following information was found to beuseful to me and may also prove to be of help toyou in preparing for painting:

U.S. Paint Corporation Application Guide,Edition 12, AWLGrip, AWLCraft 2000,AWLBrite Plus, AWLStar. U.S. Paint, 831 S.21st Street, St. Louis, MO, 63103.(314)621-0525. www.uspaint.com.

Rustoleum Industrial Coating Systems, Form No.787, Rustoleum Corp., 11 Hawthorne Parkway,Vernon Hills, IL, 60061. (800)553-8444.www.rustoleum.com.

Also: Rustoleum Labor Saver IndustrialEnamels, Form No. 8964; Rustoleum LaborSaver High Performance Epoxy 9100 System,Form No. 8706; Rustoleum 9200, 9300 and 9500Industrial Epoxies, Form No. 1003; RustoleumIndustrial Urethane, Form No. 1005.

Ketone Industrial has a good description of theDuPont coatings line (industrial, not automotive)at www.ketoneindustrial.com.

Griggs Paint at www.griggspaint.com has aprogram that you can download that will ask youabout your paint application and select paintsfrom their line which includes paints formulatedto solve the tough problems experienced by theaerospace industry.

Anchor Paint at www.ajy.net/anchor is a smallpaint manufacturer that has everything you’dwant. The Ancothane 9400 is an acrylic urethanewhich is supposed to be even tougher thanpolyurethane.

Benjamin Moore can be found atwww.benjaminmoore.com. They have a hugesupply of interior and exterior paint and can tintit to any color you want.

Kelly-Moore (Ben’s sister?) is atwww.kellymoore.com. They have a complete setof spec-sheets available along with charts thatsuggest interior paint systems.

If you want to read about how the car guys paintautomobiles, the two Paint FAQs atwww.freenet.edmonton.ab.ca/~bobstory andwww.webspan.net/~panhead/pan10.htm arepretty good.

A nice little survey publication of alternativepaint stripping methods can be found in a Guideto Cleaner Technologies, Organic CoatingRemoval, EPA/625/R-93/015, US EPA, Office ofResearch and Development, Washington, DC,20460.