United StatesDepartment ofAgriculture

Forest Service

ForestProductsLaboratory

ResearchPaperFPL-RP-494

Controlling Decay inWaterfront StructuresEvaluation, Prevention, andRemedial Treatments

Terry L. HighleyTheodore Scheffer

Abstract Note

Decay in waterfront structures results in expensive re-pair or replacement of the damaged components. Thismanual describes the problems caused by decay andways to avoid or control decay. The information pre-sented is directed toward personnel who inspect andmaintain waterfront structures. The manual describes(1) types of deterioration and underlying causes,(2) construction practices that contribute to decay,(3) decay detection, and (4) decay prevention, includ-ing remedial measures for decayed structures.

Keywords: Wood decay, waterfront structures, woodmaintenance, wood inspection

September 1989

Highley, Terry L.; Schaeffer, Theodore. 1989. Controlling decayin waterfront structures: evaluation, prevention, and remedialtreatments.

Res. Pap. FPL-RP-494. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory. 26 p.

A limited number of free copies of this publication are avail-able to the public from the Forest Products Laboratory, One

Gifford Pinchot Drive, Madison, WI 53705-2398. Laboratorypublications are sent to more than 1,000 libraries in the United

States.

This publication reports research involving pesticides.It does not contain recommendations for their use,nor does it imply that the uses discussed have beenregistered. All uses of pesticides must be registered byappropriate State and/or Federal agencies before theycan be recommended.

The use of trade or firm names in this publication isfor reader information and does not imply endorsementby the U.S. Department of Agriculture of any productor service.

The Forest Products Laboratory is maintained in cooperationwith the University of Wisconsin.

Contents

Page

Introduction . . . . . . . . . . . . . . . . . 1

Causes of deterioration . . . . . . . . . . . . 1

Biological causes . . . . . . . . . . . . . . 2

Decay fungi . . . . . . . . . . . . . . . 2

Insects . . . . . . . . . . . . . . . . . 2

Physical causes . . . . . . . . . . . . . . 5

Chemical causes . . . . . . . . . . . . . . 5

Conditions for decay . . . . . . . . . . . . . 5

Decay sites . . . . . . . . . . . . . . . 5

Decks . . . . . . . . . . . . . . . . . . 6

Surface checks . . . . . . . . . . . . . 6

Exposed ends . . . . . . . . . . . . . . 6

Wetted wood . . . . . . . . . . . . . . 6

Double-plank construction . . . . . . . . 6

Leakage through blacktop or

concrete overlay . . . . . . . . . . . . 6

Improper positioning of plank

heartwood . . . . . . . . . . . . . . 8

Curbs, chocks, and wales . . . . . . . . . . 8

Seasoning and weather checks . . . . . . . 8

Infection through bolt holes . . . . . . . . 8

Lap-joint construction . . . . . . . . . . 8

Curb splits . . . . . . . . . . . . . . . 8

Improper positioning of timber

heartwood . . . . . . . . . . . . . . 8

Stringers . . . . . . . . . . . . . . . . . 8

Checks and splits . . . . . . . . . . . . 11

Water entry along driftpins . . . . . . . . 11

Fender piles . . . . . . . . . . . . . . . . 11

Decay detection . . . . . . . . . . . . . . .

Page

12

General inspection procedures . . . . . . . . 12

External evidence of decay . . . . . . . . . 14

Methods for finding internal decay . . . . . . 14

Sounding . . . . . . . . . . . . . . . . 17

Boring . . . . . . . . . . . . . . . . . 17

Drilling . . . . . . . . . . . . . . . . 17

Probing . . . . . . . . . . . . . . . . 17

Sequential process for detecting

decay . . . . . . . . . . . . . . . . 18

Decay prevention . . . . . . . . . . . . . . . 19

Preservative treatment . . . . . . . . . . . 19

Maintenance program . . . . . . . . . . . 19

Moisture control . . . . . . . . . . . . . . 20

In-place surface preservative

treatment . . . . . . . . . . . . . . . 21

Decks . . . . . . . . . . . . . . . . . 22

Curbs, chocks, and wales . . . . . . . . . 23

Piles . . . . . . . . . . . . . . . . . . 23

Remedial measures . . . . . . . . . . . . . 23

Replacement . . . . . . . . . . . . . . 23

Reinforcement . . . . . . . . . . . . . 24

Fumigant treatment . . . . . . . . . . . 24

Precautions . . . . . . . . . . . . . . . . . 25

References . . . . . . . . . . . . . . . . . . 26

Controlling Decay inWaterfront Structures

Evaluation, Prevention, andRemedial Treatments

Terry L. Highley, Supervisory Research Plant PathologistForest Products Laboratory, Madison, WI

Theodore Scheffer, Research AssociateOregon State University, Corvallis, OR

Introduction

The primary purpose of this manual is to provide in-formation on the characteristics of decay in wood com-ponents of waterfront structures and on the means toavoid or control decay. Most measures to protect woodare directed against three types of destructive agents:(1) biological (destructive utilization of wood by vari-ous micro-organisms such as decay fungi), (2) physical(damage by breakage or deformation), and (3) chemi-cal (such as electrolytic breakdown around iron fasten-ers). Biological deterioration definitely constitutes thelargest proportion of damage to structures.

Proper construction and utilization of appropriatepreservative-treated materials are the primary ingre-dients for a long-lasting structure. However, good con-struction needs to be backed up by good maintenance.Deterioration often advances slowly and is not imme-diately obvious. By the time deterioration is apparent,the trouble may be widespread. Routine inspectioncan identify potential or actual problems before theybecome severe. Corrective measures at early stagesmay entail minor expenses, but if the deterioration isallowed to continue, the result may be costly majorrepairs or even complete demolition of the structure.

Data derived from a well-organized and executed in-spection and maintenance program can be valuable forplanning new construction that will be free from theconditions that favor deterioration. Comprehensive in-formation about the current condition of the structures

can also prevent expensive replacements and loss ofservice time during repairs. Thus, when the total costand service value of military and commercial marineinstallations are considered, the relatively small sumsof money expended for decay-inhibiting construction,adequate routine inspection, and proper preventivemaintenance are clearly cost-effective.

This manual is concerned almost exclusively with bi-ological deterioration caused by decay fungi in theabove-water portions of waterfront structures. Below-waterline decay is not a problem. The manual isdivided into three major areas: (1) deterioratingagents, (2) decay detection and evaluation, and (3) de-cay prevention and remedial treatment. Many portionsof the information were derived in collaboration withthe Department of the Navy.

Causes of Deterioration

Wood does not deteriorate as a result of aging alone.The service life of all commonly used constructiontimbers depends on their protection from a varietyof deteriorating agents by means of construction andmaintenance procedures suited to the physical andclimatic features of the construction site. Deterio-ration of wood usually falls into one of three prin-cipal categories: (1) biological, (2) physical, and(3) chemical.

Biological Causes

Biological damage to above-water parts of waterfrontstructures is caused directly or indirectly by the activ-ity of fungi and insects that utilize the wood for foodor nesting material.

Decay Fungi

Decay fungi are primitive plants that obtain their foodfrom wood (Fig. 1); they cause by far the greatestamount of damage to the above-water components ofwaterfront structures. In fact, the service life of wa-terfront wood is most commonly terminated as a re-sult of decay. If wood is kept in a damp condition forany length of time, it becomes infected with fungi thatcause decay. The rate of wood degradation depends onthe species of fungus and the kind of wood. Degrada-tion results in loss of weight and strength of the wood.

The growing stage of the fungi is characterized by mi-croscopic threads called hyphae that develop from ger-minating spores, which are analogous to seeds. Thehyphae penetrate and ramify within the wood andcause the chemical and physical changes recognized asdecay. Under suitable conditions, fungi produce spore-bearing structures called fruit bodies, from which thefungus generally reproduces and spreads. Many de-cay fungi can be recognized as mushrooms or bracket-shaped fruiting bodies on the surface of the infectedwood. Thousands of microscopically sized spores, anal-ogous to seeds of higher plants, are produced in thefruit bodies and released into the air. When the tem-perature is mild, spores contacting susceptible moistwood can germinate and cause new infection.

Conditions for Growth — In common with mostorganisms, decay fungi require oxygen and favorablemoisture and temperature. Oxygen is ordinarily nota limiting factor except for wood that is under wa-ter or deep in the ground. Wood moisture contentsfrom about 40 to 80 percent based on ovendry weightare most favorable for decay. These amounts of mois-ture occur only in green wood or as a result of wet-ting. Therefore, if wood is dried and then protectedagainst wetting, it will not decay. For a recommendedmargin of safety, untreated wood should not be usedin an environment with a moisture content exceeding20 percent. Moisture absorbed from humid air alone(no condensation) will almost always meet this limi-tation. By contrast, very high moisture contents canprevent rather than favor decay. Thus, saturated woodthat has been continuously under water can remain

comparatively sound for many years. The high mois-ture level prevents needed access of oxygen to typicaldecay fungi.

Decay fungi differ in temperature for optimum growth.The optimum range for most decay fungi is from about21°C to 30°C, although some species grow slowly attemperatures as low as 0°C and as high as 45°C. Inmany areas, low temperatures from late fall to earlyspring either minimize or prevent decay. The optimumpH is in the range of 4.5 to 5.5.

Above-ground wood is less susceptible to decay thanwood in contact with the soil. This results in partfrom the typically drier environment and the fact thatthe wood is not in contact with decay fungi alreadyestablished in the soil. The infection of above-groundwood depends almost solely on infection by fungalspores, which are relatively sensitive to environmentalextremes and toxins. Natural wood extractives thatare relatively low in toxicity or lower concentrationsof wood preservatives will prevent spore infection asopposed to infection by fungi growing in and nourishedby soil nutrients.

Classification — Typical wood decay fungi fall intotwo broad classes: brown rot and white rot. Thebrown-rot type of decay is much more common inwaterfront timbers, which largely are pine or Douglas-fir. Brown-rot decay is usually not seen on the sur-face of timbers protected by preservative treatmentor in untreated members, which are protected by in-termittent surface drying. Typical brown rot can berecognized by the color and physical character of thedecayed wood. Wood with advanced decay caused bybrown-rot fungi is brittle, exhibits abnormal shrinkagewhen dry, is usually brown, and typically shows dis-tinct cross-grain checks, similar to those on the face ofheavily charred timber (Fig. 2).

White-rot fungi may occasionally be found in water-front members made of hardwood species such as oak.The decayed wood does not shrink abnormally; it maybe whitish or light tan and flecked with dark pencil-like lines (zone lines). Typically, wood is not checked(Fig. 3) and may have a distinctly soft and punky tex-ture despite the absence of abnormal shrinkage.

Insects

Insect damage to the above-water components of wa-terfront structures is not nearly as common or destruc-tive as decay, but it nevertheless needs to be recog-nized (Fig. 4). Extensive insect activity usually results

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Figure 1—Examples of fungal growths andassociated wood decay. (A) Fruiting bod-ies; (B) advanced wood decay; (C) fruitingbodies-obvious decay on wood surface;(D) fungal growth on wood surface and ad-vanced decay shown by checks both acrossand with grain. (M 31901F)

Figure 2—Stages of brown-rot decay (Top)Early stage-discoloration in surface andend grain (left). (Bottom) Late stage–cracked and collapsed wood. (M 124 928)

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Figure 3—White-rot decay (Top) Mot-tling and dark zone lines (arrows) bor-dering the abnormally light areas in endgrain. (Bottom) Side grain in same board.(M 124 927)

Figure 4—Types of insect damage mostlikely to occur in a building. (Upper left)Termite attack-feeding galleries (oftenparallel to the grain) contain excrementand soil. (Upper right) Powder-post bee-tle attack-exit holes usually filled withwood flour and not associated with dis-colored wood. (Lower left) Carpenter antattack-nesting galleries usually cut acrossgrain and are free of residue. (Lower right)Beetle at tack-feeding galleries (madein the wood while green) free of residueand surrounding wood darkly stained.(M 124 884)

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in the distortion of shape and collapse of structuralmembers. Various types of termites, beetles, carpenterants, and bees utilize wood as a food source or fornesting purposes. Damage by wood-boring insects canusually be recognized without difficulty. Evidence oftheir presence may be entrance or departure holes,which vary in size according to the type of insect. Inmany instances, the accumulation of powdery materialin the vicinity of the hole indicates insect activity.

In general, attack by termites is more destructive thanthat by other insects. Termites work inside the tim-bers, eating the wood and excavating large tunnelsand galleries, which sometimes hollow out the tim-ber completely. Termites never form exit holes on thewood surface; they carefully avoid damaging the sur-face. However, earthen tunnels or tubes on the woodsurface, which conceal the passage of the insects fromplace to place in the wood, may indicate termite infes-tation. In the United States, termites are a problemmainly in the South, but they may be troublesome inany mild climate.

Wood rarely comes into contact with strong chemi-cals in waterfront structures, except in the case of ac-cidental spilling. Most frequently, chemical damage ofwooden components is associated with metal fasteners(Fig. 5). Wood adjacent to iron nails, screws, bolts, orother fasteners becomes blue-black and in time softensto varying degrees. This type of damage is commonlyreferred to as “metal sickness;” the chemical deteri-oration is often confused with decay caused by fungi.In advanced stages, the wood adjacent to fastenersappears to be charred and breaks into small, cubicalpieces. A similar chemical effect has been observedaround copper or copper-alloy fasteners.

Conditions for Decay

Decay Sites

For members exposed above water or ground, weatheror seasoning checks can provide a locus for decay.

Physical Causes

Physical damage can result from overstressing, whichcauses excessive deflection of structural members oreven failure to carry load. When wood members areloaded beyond their capacity for a long time, the fibersbecome permanently elongated in a process referred toas creep. Overload may be due to greater-than-designloading or to high moisture content of the wood, whichreduces stiffness. Although deflection may not indicateloss of strength, the sag is usually permanent.

Wood is also overstressed by high-impact loading. Im-pact from berthing and mooring of ships is the chiefcause of failure of fender piling. As wood dries, shrink-age may cause checks and splits. Checks may aggra-vate mechanical failure of deck surfaces subjected toconsiderable vehicular traffic.

Intermittent wetting by sea water occasionally causesa type of physical damage called shredding. The saltin the water accumulates and the resultant bulk causesthe wood fibers to separate; the surface of the affectedmember consequently appears shredded.

Chemical Causes

If wood comes into contact with certain chemicalssuch as strong acids or alkalis, some of the wood con-stituents may be decomposed.

Figure 5—Chemical damage to woodcaused by corrosion of metal fasteners.(M 144 736)

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Large solid-sawn members are commonly subject toseasoning checks. When members are positioned hor-izontally as in decking, stringers, and curbing, anychecks on their upper surfaces and some checks on ex-posed side surfaces become water traps if the membersare subjected to rain or other forms of wetting. Verti-cally positioned members with comparable checks com-monly remain dry since most checks can drain freelywhen wetted.

Another point of localized wetting in waterfront mem-bers that is conducive to decay is at wood-penetratingfasteners or hardware. Water, carrying fungus spores,may move in alongside bolts and nails and conse-quently wet and infect the interior wood. The rate ofsubsequent drying of the wood is comparatively slow,and so the wood tends to remain wet between rains.Predrilling timbers prior to pressure-preservative treat-ment can eliminate the danger of decay contributed bybolt holes.

Water penetration into wood can also be significantlyinfluenced by the grain of the wood. End-grain (cross-cut) surfaces of wood absorb water much more rapidlythan side-grain surfaces because permeability in thelongitudinal (grain) direction tends to be 50 to 100times greater than in the transverse (across-grain)direction. Thus, when water enters a bolt or fastenerhole, it is absorbed largely along the grain where it canbuild up to critical amounts around the hole. Becauseof the prominence of end grain in wood, butt joints ofuntreated wood are especially vulnerable to wettingand decay.

Decks

Deck decay is illustrated in Figures 6 through 10.Practically all decking on waterfront structures is ei-ther Douglas-fir or Southern Pine. Conditions leadingto decay in decks are the same for both species, butthe rate of deterioration in untreated decks is consider-ably faster in pine than in Douglas-fir.

Surface Checks

Weather checking of the upper surface of planks is aconspicuous feature of decks that have been in servicefor a few years (Figs. 6,7). Checks can promote decayin two ways: (1) by creating cavities in which rainwa-ter is trapped, thereby wetting the wood sufficientlyto support attack by decay fungi, and (2) by pene-trating a zone of treated wood and thereby exposingthe underlying untreated wood to infection. Moreover,

weather checks not only promote decay but may alsoerode the deck surface and increase the rate of deckwear from traffic.

The rate of decay from checks in deck planks as wellas heavier wood members can accelerate over time.Over a period of years, incipient infection can getestablished in numerous checks without causing con-spicuous breakdown of wood; once the attacking fun-gus is established in the interior of the wood, decaycan proceed rapidly to the visible stages.

Exposed Ends

Decay can enter pressure-treated planks and timbersthrough the ends where untreated wood is exposedby cutting the members to length. If the untreatedends are butted together, a water-trapping butt jointis created and serious decay may result in a short time.Untreated wood ends should be protected by floodingwith a strong solution of preservative.

Wetted Wood

Wetting decks and supports with freshmaterially shorten their service life.

water may

Double-Plank Construction

The double-plank type of construction is an invitationto decay because the two layers of planks provide aninterzone in which water can be trapped. The deckshould contain only a single layer of planking, and theplanking should be spaced to let water pass throughthe deck freely.

Leakage Through Blacktop or Concrete Overlay

Although an asphalt or concrete surface may appear toprovide a good protective cover against rain, it doesnot necessarily do this. Cracks frequently develop,particularly with blacktopped surfaces (Fig. 8), andrainwater consequently penetrates to the underlyingplanking and supporting wood members. The deckcover retards subsequent drying, making a favorablecondition for serious decay.

Another place of decay-promoting leakage throughblacktopped and concrete decks is between the trackrails and the blacktopping or concrete in which therails are embedded (Fig. 9). Such leakage can be espe-cially hazardous because the depression in the blacktop

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Figure 6—Weather checking in upper sur-faces of pier and wharf planks. A, Crosssection of Douglas-fir plank showing typ-ical preponderance of checking on upperweather side and rot in some checks result-ing from trapping of rainwater. B, Decay,promoted by weather checking, extend-ing close to surface of Douglas-fir deck.(M 130 017)

Figure 7—Cross-sectional view of planksshowing decay in one check. Stringer withdecay on upper surface also shown.

Figure 8—Blacktop cover should be prop-erly constructed and maintained to ade-quately protect deck against rain wettingand decay. A, When the track area is de-pressed to accommodate wheel flanges, ittends to collect water from adjacent area.B, Cracked blacktop.

Figure 9—A concrete deck may leak attrack positions and wet wood directly un-derneath. Here, decay has started alongtop of stringers.

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or concrete adjacent to the rails, necessary to accom-modate wheel flanges, has a funneling effect, tendingto bring water from surrounding areas toward the rails.

Improper Positioning of Plank Heartwood

The heartwood-containing face of pine deck planksshould be positioned downward because the heartwoodmay be poorly treated (Fig. 10) and because deckdecay largely occurs in the upper zone of the plankingas a result of weather checking. Heartwood from nearthe pith zone should also be positioned on the lowerside of the planks because this wood is relatively weakand easily broken; hence, it performs poorly undertraffic.

Curbs, Chocks, and Wales

Although they are not supporting members, curbs,chocks, and wales are large and relatively expensivetimbers, fully deserving protective measures. Furtherjustification for their protection is the high labor costfor replacement. Although comparatively accessible,such timbers resist removal because they are stronglyattached to the structure and commonly carry a heavycomplement of cables and pipes.

Decay of curbs, chocks, and wales can be preventedby deep preservative treatment, as is the case in treat-ment of pine sapwood. Decay in treated pine productsis usually well-controlled irrespective of constructionpractices, mishandling, or long exposures. When thewood is not treated, or when the treatment is not verydeep (as is typical in Douglas-fir), various conditionscan lead to serious decay.

Seasoning and Weather Checks

As with deck planking, checks developing in the upperportion of curbs, chocks, and wales are the main causeof prolonged wetting and decay in these heavier mem-bers (Fig. 11). Both seasoning and weather checksare prevalent; because the members are large (at least10 in. (25.4 cm) on a side), they are usually not fullyair-dry before placed in service. The large size of theitems moreover favors the development of especiallydeep checks. Such checks do not dry as rapidly as theshallower checks in planking, and thus, they present amore severe decay hazard. In treated Douglas-fir tim-bers, the larger checks typically extend well below theouter preservative-containing zone of wood (Fig. 11),exposing the untreated wood to infection.

Infection Through Bolt Holes

Bolt holes are also a common focal point for decay.When the holes are drilled in treated timber on theconstruction site, the drilling exposes untreated woodadjacent to the bolt (Fig. 12).

Lap-Joint Construction

The common lap-type joining of ends favors decay incurbs and wales. The half-lap joint is most common,and a similar connection, the oblique-scarf joint, isoccasionally seen (Fig. 12). The lap-type joint accen-tuates the decay hazard at the ends of timbers in twoways: (1) by exposing a large amount of untreated in-terior wood in treated Douglas-fir timbers and (2) bycreating a relatively large interfacial zone where watercan be trapped. This kind of joint is also objection-able because effective on-site treating of newly exposedwood is especially difficult. Because much of the newsurface is side grain, penetration of a preservative solu-tion, applied by brushing or spraying, tends to be veryshallow.

Curb Splits

Splits are occasionally formed in curbs as the result ofstresses on mooring cleats (Fig. 13). Such openingsfavor decay in the same way as checks that developfrom seasoning or weathering.

Improper Positioning of Timber Heartwood

As in deck planks, placement of a heartwood face canaffect the hazard of decay in pine curbs, chocks, andwales. Heartwood is commonly present on one face; itreceives little preservative. Consequently, timbers withheartwood should be positioned with the heartwood-containing face downward, where the fewest weatherchecks develop.

Stringers

Failure of stringers is obviously one of the costliestforms of damage to waterfront structures because thesetimbers are a major load-bearing component. Toreplace stringers, all members that they support mustbe removed. Most decay in stringers begins along theupper face, and even at early stages, decay may loosendeck spikes. Stringer decay generally originates inchecks and splits caused by plank spikes and alongdriftpins (Fig. 14).

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Figure 11—Potential decay sites for curb,chock, and wale timbers. A, Weatheror seasoning checks in upper surface ofDouglas-fir curb. B, Deep weather checksin pressure-treated curb penetrate thetreated zone and subject interior wood todecay. (M 145 019)

Figure 10—Heartwood and sapwood inSouthern Pine deck planks. A, Deck plankwith heartwood in upper surface andwood near pith, which cause an unusuallycracked and weakened surface. B, Timbersin cross section showing typical distributionof preservative in heartwood and sapwood.

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Figure 12—Half-lap-type end-joints and driftpins are prominent points of water entryinto Douglas-fir curbs and whales and thus favor decay. (Upper left) Curbing fastenedtogether with an oblique scarf joint. (Upper right) Joined curbs with two unneces-sary features favoring decay: half-lap joint and four bolts used to attach curb to deck.(Lower left) Deteriorated half-lap joint between curbs. (Lower right) Rot in curb fromwetting around driftpin.

Figure 13—Curb splits caused by twisting and pulling of mooring cleats. A, Typicalcurb split produced by stressing of mooring cleat. B, Resultant decay.

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Water Entry Along Driftpins

Figure 14—Typical stringer decay. A,Extensive decay in untreated Douglas-firstringer. B, Loosening of deck planks onDouglas-fir stringers caused by rotting ofwood holding stringer spikes.

Checks and Splits

Driving deck spikes directly into the wood generallycauses a split in the stringer. The splits may be quitesmall and inconspicuous, but even so they furnish aplace where water can collect. Splits are likely to belargest near the ends of the stringers. The tendencyto splitting can be aggravated in two ways: by driv-ing the spikes in line along the grain of the stringersand by using larger spikes than needed. Presumably,oversized spikes are used for convenience.

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Although holes are drilled for driftpins, thus preclud-ing splitting of the stringer, water and fungi neverthe-less can enter the stringer alongside the pin. The holeenlarges somewhat with time as the wood shrinks andswells with weather changes. This increasingly addsto the space between pier and wood, thereby creat-ing more and more opportunity for wetting and decaydeep in the stringer (around the driftpin).

Fender Piles

Premature failure of marine piling because of interiordecay is a major problem, which leads to costly repairsor replacement of the wood. The U.S. Navy estimatesthat over $5 million a year are spent for pile replace-ment (personal communication, Robert Page, formerlyNaval Facilities Engineering Command, 1973). Thedamage is particularly serious in fender piles, whichare required to protect both the docking vessel and thepier or wharf from possible impact damage.

The problem is strictly one of treated piling, since un-treated piles will fail from marine-borer attack beforesignificant decay occurs. The principal woods used forfender piles are Douglas-fir and Southern Pine; oak isused in moderate quantity. Southern Pine fender pilesthat are treated according to recognized standardshave little problem with decay; the treatment can pen-etrate deeply because most of the wood is sapwood(Fig. 15). Decay occurs mainly with other species, es-pecially Douglas-fir, which have relatively narrow sap-wood and therefore cannot be treated deeply (Fig. 15).Piles with narrow sapwood have an untreated heart-wood center surrounded by a treated outer shell. Theuntreated heartwood can constitute a considerable por-tion of the total pile volume. Thus, the primary av-enue of infection by decay fungi is through the timberends where untreated wood is exposed after the pilesare cut to desired height. Decay in Douglas-fir fenderpiles starts at the top and progresses downward intothe central column of untreated wood. Rate of down-ward progress may be about 1/2 ft (15.24 cm) peryear. Pile decay eventually extends to the high-waterlevel, where water soaking of the wood inhibits furtherprogress of the fungus. Practically all the above-waterportion of the pile can become decayed on the insidewithout apparent decay on the exterior shell of treatedwood. The resultant lack of interior strength undoubt-edly is responsible for much pile breakage. Yet, thisindirect but seriously damaging effect of decay seemsto be largely unrecognized.

Figure 15—Effectively and ineffectively treated piling. A, Effectively treatedSouthern Pine piling. Little untreated wood is exposed by weathering checks, notching,or boring. B, Heavily checked Douglas-fir pile; checking developed in pile 5 years afterinstallation. C, Typical interior rot in pressure-treated Douglas-fir pile not treated atcutoff.

Although those who maintain fender piles recognizethat untreated wood exposed in cutting or boring onthe construction site should be at least brush treated,they frequently do not know the limitations of thisform of treatment and the need for a pile cover to sup-plement the preservative treatment. A cover aloneis not likely to be effective (Figs. 16,17). Moreover,even those who are aware of the need for both preser-vative treatment and pile covers overlook certain re-quirements for the effective application of these protec-tive measures. Prompt application of an appropriatepreservative and cover to the cut surface can protect apile top against decay. The treating must be done be-fore decay gets established. Often, covers are appliedwithout accompanying preservative treatment underthe misconception that the covers will protect againstrain and thus prevent sufficient moisture build-up fordecay. Simply excluding rainwater from fender pilesis not a dependable protection against decay. Decayfungi can get established early, and moisture alreadypresent in the pile is usually sufficient to support decayindefinitely.

Another practice that leads to fungal infection isnotching of the pile to receive the ends of chocks orto accommodate planks used in constructing double-membered caps (Fig. 18). As noted with timbers, thiscutting exposes untreated wood. Sometimes the fenderpiles are notched to receive the ends of the chocksmore snugly than if they were simply butted against

the pile. This practice has no real merit and there-fore should be avoided, at least with Douglas-fir or oakpiles, because in these species the notching generallywill expose untreated wood. Moreover, the untreatedpile wood cannot be protected in depth by superficialsupplementary treating because the surface consists ofside grain, which is penetrated only slightly by brushedor sprayed preservative solution. However, some evi-dence indicates that wood in joints can be adequatelyprotected by shallow penetration of the preserva-tive if the preservative is applied in high enoughconcentrations.

Decay Detection

General Inspection Procedures

Structures should be inspected routinely, and a recordshould be kept of the extent of decay and the kind ofstructural members affected by decay. Such a record isnecessary for an efficient maintenance program.

The climate index map for decay hazard shows theeffect of geographic location on the rate of decay(Fig. 19). The most severe location in the UnitedStates is the Southeast, where rainfall is plentiful andthe weather is warm and humid. In the Northeast andMidwest, decay advances at a somewhat slower rate.

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Figure 16—Covers for fender pile cutoffs.A, Pile capped with raised metal collar;hot bitumen was poured inside the collar.B, Copper cover rendered ineffective byhawser chafing and vandalism.

Figure 17—Bituminous coatings. A, Effec-tive bituminous cover on Douglas-fir fenderpile. B, Ineffective bituminous cover.

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Figure 18—Piles notched to provide firmercontact between wale and pile or to provideshoulders to support clamps. This practicedoes not prevent decay.

Near the coast in the Northwest, decay hazard is mod-erate, but it can be severe on the coast. Most of theSouthwest is very dry, so the decay hazard is minimal.

The inspector should formulate a general plan ofprocedure by collecting any drawings, specifica-tions, and data pertinent to the service history of theitems to be protected. The age, size, and design ofindividual waterfront structures dictate in part the in-spection procedures and the equipment required for athorough inspection. Any available records of previ-ous inspections, damage, repair, member replacement,or structural modification should be noted with theirrespective dates.

The actual equipment necessary for examining water-front structures is relatively simple. It should includehand tools for measuring, sounding, probing, drilling,and boring, and an instrument for measuring woodmoisture content. A camera, ideally with flash attach-ment, is useful for providing a photographic record ofunusual circumstances.

External Evidence of Decay

locations or conditions most conducive to prolongedwetting (Fig. 20). Decay usually results in abnormalcoloration of the wood. The first indication of decayis often brown streaks or blotches; purplish streaks aresometimes present (Figs. 2,3). As wood approachesadvanced stages of decay, it loses luster and may ex-hibit pronounced changes in color. Of course, judg-ments based on color necessitate familiarity with theappearance of sound wood. Sound, healthy softwoodhas a pleasant, fresh, resinous smell, whereas decayedwood usually has a mushroom-like, stale odor. How-ever, a musty, moldy smell, though indicative of dam-age conditions favorable to decay, does not necessarilyindicate the presence of decay.

The presence of fruiting bodies or “mushrooms” usu-ally indicates that decay has become well establishedin the members (Fig. 21). Advanced decay is also easyto recognize from changes in the physical appearanceof the wood, such as localized depressions or sunkenareas over decay pockets, which reflect loss of woodsubstance beneath, and cracking in cubical patterns,which results from wood shrinkage. Evidence of re-tained moisture over a period of time, especially at thejunction of timbers, often indicates fungal attack.

Inspections for decay are most critical in those situa-tions that favor decay. For example, visual evidenceof hazardous moisture conditions calls for special at-tention. Evidence of persistent water may appear aswatermarks. Rust stains on wood surfaces may alsoindicate excessive wetting, particularly if the sourceof the iron is a wood-penetrating fastener. Apprecia-ble growth of moss or other vegetation on wood sur-faces or in checks or cracks is evidence of potentiallyhazardous wetting.

A small measuring tape should be available to measurethe extent of decay and width or length of checks andsplits. Another helpful tool is a thin ruler, or feelergauge, to determine depth of checks or condition offasteners at joint interfaces. A moderately pointedtool such as an ice-pick or sharp-bladed screwdriveris useful for probing suspected areas of decay.

Methods for Finding Internal Decay

Simple methods are available for inspecting waterfrontstructures without sophisticated tools. These methods,which include “sounding,” boring, drilling, probing,and measuring moisture content, may be used singly orin combination.

A good way to begin an inspection for decay is avisual search for decay manifestations, emphasizing

14

Figure 19—Climate index for decay hazard. Higher numbers indicate greater decayhazard. (M 144 642)

15

Figure 20—Schematic of typical areas of decay in decking,stringers, pile covers (caps), curbing, and piling.

16

Figure 21—Decay fungal fruiting bodies ingrowing (fresh) condition.

Sounding

Sounding, by rapping on the member with a hammer,may indicate the presence of interior deterioration.If the hammer does not rebound or produces a dullor hollow sound, a considerable amount of the inter-nal wood is probably decayed. This method requiresconsiderable experience and can be considered trulydiagnostic only where decay is relatively severe, wherelarge members are decayed, and where the decay ex-tends to areas near the surface. If sounding suggestsinternal decay, the wood must usually be bored to ver-ify the diagnosis.

Boring

Boring with an increment borer is the most widelyused technique for detecting internal decay. The ad-vantage of this method is that the removed incrementcore provides an actual specimen in which the damage

can be seen. This method should be limited to areaswith conditions suitable for decay. A sharp boring bitshould be used because a dull one tends to crush orbreak wood fibers and to change the appearance of thesample. Inspectors should carry extra drill bits; cut-ting edges are easily damaged beyond practical fieldmaintenance when a bit strikes hidden fasteners. Boreholes may become avenues for decay, and so the holesshould be properly treated. Following extraction of thecore, a wood preservative should be squirted into thehole and the hole plugged with a preservative-treatedwood dowel.

Similarly, a plug cutter can be used to examine in-ternal wood for decay. Plug cutters of 1/8 to 1 in.(0.32 to 2.54 cm) diameter have been used. The3/8-in. (0.96-cm) plug cutter is very popular becauseit is commercially available, it creates only a small holein the member, and the samples obtained can be usedin a biological assay if necessary. The holes should befilled with preservative-treated plugs. In addition, apreservative should be squirted into the holes beforeplugging. A saw is useful for cutting off plugs flushwith the surface.

Drilling

Drilling into the member with a sharp 1/4-in. (0.63-cm)(approximate) bit can often be useful. A noticeabledrop in resistance to the penetration of the drill indi-cates decay. Chips of decayed wood brought out bythe drill tend to be darker and more easily crushed be-tween the fingers than chips of sound wood.

Probing

Sometimes the outer surface of members consists ofonly a thin solid shell and the wood underneath isdecayed. This condition can be detected by prob-ing. Fungal decay causes wood to soften and lose itsstrength. If decay is suspected, the area should beprobed with a pointed tool or a blade and the resis-tance of the wood compared with that of obviouslysound wood. Areas where water is likely to be ab-sorbed or trapped by wood, such as end-grain or side-grain faces adjacent to joints, should be probed. Amoderately pointed tool such as an ice-pick or sharp-bladed screwdriver is useful for probing. Early decaymay be detected by jabbing the probe into the woodand prying down. Sound wood, which is relativelytough, usually breaks out in long splinters, whereasdecayed wood, which is brittle, breaks out abruptlyacross the grain in short pieces (Fig. 22).

17

Figure 22—Probing test for early decay. (Left) Sound wood priesout as long splinters. (Right) Decayed wood breaks abruptlyacross grain without splintering. (M 124 721)

During inspection of wood, information about woodmoisture content is often helpful. A resistance-typemoisture meter is ideal for such a purpose becauseit is simple to use and nondestructive. A reading of>20 percent moisture content indicates that the woodis susceptible to decay.

Moisture meters employ two elongated probes or pinsattached to a resistance meter. The meter is read atselected points as the pins are driven into the wood.Whether or not moisture conditions are conducive todecay can be determined by taking moisture readingsat various sites with decay potential. Moisture read-ings above 25 percent after a few days of dry weatherindicate that the wood is not safe, if untreated. Mois-ture meters are effective only up to a depth of 3 in.(7.62 cm), the maximum probe penetration.

For accurate readings, the meter should be frequentlycalibrated and the batteries should be checked to as-sure that the electrode coating is intact. When usingthe moisture meter in extreme cold or heat, the read-ings should be corrected for temperature and woodspecies. Thus, temperature should be recorded alongwith the meter reading. The meter manufacturershould supply the information necessary for the cor-rections. A moisture meter will not give correct read-ings in wood treated with chromated copper arsenateor ammoniacal copper arsenate or in wood that hasbeen subject to wetting by sea water. The conduc-tive elements in these materials cause erroneously highreadings.

Sequential Process for Detecting Decay

1. Observe and record condition of wood. Initially, ob-serve and record the general condition of piles, crossbracing, stringers, caps, curbs, wales, chocks, and deck-ing. Probe suspicious areas for the presence of decaynear the surface of timbers. Note any unusual damage,loose bolts, chafing about the waterline, deep checks,cracks, scars exposing untreated wood, and untreatedcut-off tops and ends of pilings and other members.Also examine the surfaces for holes made by pointedtools, exit holes made by beetles, piles of sawdust leftby carpenter ants, mud tunnels made by subterraneantermites, or wings discarded by reproductive termites.

2. Sound members. Next, sound the members with ahammer, listening for an abnormal response. Suspi-cious areas should be bored to determine the natureof the defect. Sounding will detect only members withserious internal defects and should never be the solemethod of inspection.

3. Drill members at suspicious sites. After sounding,drill or core members at sites where decay is suspected,emphasizing positions adjacent to the widest checks.Samples may be collected and submitted to a labora-tory for analysis, such as culturing for decay fungi orpreservative retentions. Aluminum foil, plastic bags,and glass or clear plastic vials are useful for transport-ing samples for further analysis.

18

4. Drill members at other sites. If decay is visible inthe first core, drill or core the member at other sitesto determine the distribution of the decay. Measurethe depth of preservative treatment, depth of appar-ently solid wood, and size of the member. The residualstrength of the member can be estimated from thisinformation, and depending on how the structure isbeing used, decisions can be reached about future re-placement or remedial treatments. If decay is present,remember that adjacent, apparently solid, untreatedwood is probably in the early stages of decay.

5. Treat openings and plug holes. Treat all openingsmade during the inspection with a preservative solu-tion or grease and plug the holes with preservative-treated dowels slightly larger in diameter than theinspection holes.

Decay Prevention

Preservative Treatment

Wood used under conditions conducive to decay re-quires preservative treatment for long service life. Twotypes of preservatives can be used: oil-type preserva-tives, such as creosote or petroleum solutions of pen-tachlorophenol, and waterborne preservatives, such ascopper chrome arsenate and ammoniacal copper arsen-ate. In the preferred commercial treatment, the woodis impregnated with the preservative under pressure.Under some conditions of low-to-moderate decay haz-ard (e.g., above ground), the wood can be adequatelytreated by brushing, spraying, dipping, or steeping.However, once decay is established in a member, typi-cal surface treating will not penetrate enough to erad-icate the decay. In general, preservative treating is apreventive measure, not remedial. However, fungicideshave been developed recently that penetrate deeplyinto structural timbers and eradicate internal decay.These treatments are applied as a liquid or solid indrilled holes, from which they migrate several feet(meters) as a toxic vapor.

Waterborne preservatives are desirable because theyleave the wood clean, non-oily, and paintable. For wa-terfront members, the principal disadvantage of wa-terborne salt treatment, compared to the more widelyused creosote or penta-oil treatments, is that it doesnot impart water repellency to the wood. Checkingis also generally more severe in salt-treated than oil-treated timbers. On the other hand, some evidenceindicates that checks created by certain waterbornetreatments may facilitate the passage of fungitoxicmaterials.

For material of the size and thickness commonly usedin waterfront construction, complete penetration ofthe preservative into the members is generally imprac-tical and in some woods, impossible. Instead, mostmembers are protected by impregnating the outerwood sufficiently to create a toxic outer barrier tofungal invasion. As long as this barrier is maintainedwithout breaks, fungi cannot invade the untreatedinterior wood. The effectiveness of the preservativebarrier is determined by two factors: the thicknessof the treated wood shell (preservative penetration)and the quantity of preservative in the treated wood(preservative retention).

The wood of Douglas-fir trees consists mainly of heart-wood, which is difficult to treat (Fig. 23). The treeshave a relatively thin sapwood of which only smallamounts are usually retained in heavy, solid-sawnmembers. Even small surface seasoning checks or smallfastener penetrations, such as nails, may afford avenuesfor fungi to penetrate the treated zone and reach theuntreated interior wood. Incising (a systematic pat-tern of punctures on the face-grain surfaces) is usedto improve preservative penetration and retention inDouglas-fir heartwood, and it is usually specified intreating standards.

By contrast, Southern Pine members, which have ahigh percentage of sapwood, can usually be treatedrelatively easily and effectively without incising. Thesapwood is readily treatable both in regard to pene-tration and retention of preservatives. However, theheartwood of Southern Pine, as that of Douglas-fir, is difficult to treat. The limited availability oflarge, solid-sawn Southern Pine timbers has resultedin the use of smaller, young-growth trees; glued-laminated members can be substituted for largemembers.

The moderate level of decay resistance characteristicof Douglas-fir and Southern Pine heartwood will affordsome protection in above-ground exposures where in-fection is generally limited to spore germination andwhere periods of high wood moisture content are notcommonly prolonged. However, much longer servicelife can be obtained if the heartwood is treated ade-quately with appropriate wood preservatives.

Maintenance Program

When tied to a competent inspection program, regularand timely maintenance is the most cost-effective

19

Figure 23—Cross section of incisedDouglas-fir curb showing limited penetra-tion of preservative.

approach for achieving long service life from existingstructures. Unfortunately, maintenance is frequentlyneglected until major problems develop, which eventu-ally require closing or replacing of the structure. Whenbudgets are low, the first program reduced as a money-saving measure is often maintenance; ironically, re-duced maintenance substantially increases costs in thelong term.

Maintenance of waterfront structures is commonly de-fined as those activities necessary to preserve a struc-ture and ensure the safety of users. In practice, allmaintenance is either preventive or remedial. Thatis, it is intended to prevent a future problem or correctan existing one. Maintenance of waterfront structuresmay be divided into three arbitrary categories basedon the severity or potential severity of decay: preven-tive maintenance, early remedial maintenance, andmajor maintenance.

Preventive maintenance involves keeping the structurein a good state of repair to reduce the probability ofproblems in the future. At this stage, decay or otherdeterioration has not started, but the conditions orpotential for decay is present. Preventive maintenancefor decay problems in waterfront structures has beenlargely neglected.

Early remedial maintenance is performed when decayor deterioration is present but does not affect thecapacity or performance of the structure in normalservice. At this stage, more severe structural damageis imminent unless corrective action is taken.

Some attempts at moisture control, such as the use ofroll roofing or sheet metal as water-diverting coversor caps, have not resulted in the improvement sought,and in some cases, these techniques have contributedto increased wetting. For example, roll roofing used asstringer covers under decking or as piling top coversunder caps may initially reduce wetting; however, asthe material ages and is used repeatedly, it becomespermeable to water. In either new or old condition,such material will inhibit the drying of any coveredwood that was initially wet or that has become wet.

Another example of faulty pile-top shielding is the useof sheet metal inserts between bearing-pile tops and

20

Major maintenance involves immediate corrective mea-sures to restore the structure to its original capacityand condition. Deterioration has progressed to thepoint where major structural components have expe-rienced moderate to severe strength loss, and repair orreplacement is mandatory to maintain load capacity.At this point, preventive and remedial treatments tocontrol decay are probably of little value. Therefore,this aspect of maintenance will not be addressed.

This section discusses several maintenance practicesand methods applicable to waterfront structures. Theprincipal aims of maintenance applied to decay prob-lems should be both the control of established decayand the prevention of new infections. Because deficien-cies can develop from many causes, each type of poten-tial problem cannot be addressed individually. Rather,the preventive and remedial methods presented can beadapted to the specific circumstances of the structure.

Moisture Control

Moisture control can be used as an effective, simple,and economical method for reducing decay in water-front timbers. To a large extent, moisture control in-volves a common sense approach of identifying areaswith visible wetting or high moisture content, locatingthe source of water, and taking corrective action. Inmany cases, drainage patterns can be altered to pre-vent accumulation of water on decking. General clean-ing of deck drains, deck, and other horizontal compo-nents can also maintain air circulation and preventprolonged exposure to trapped moisture. When waterenters through cracks or loose joints, covering with abituminous mastic or sealer can effectively close off thelocation and prevent further water in-flow. Althoughlittle can be done to shield members exposed to weath-ering, caps or other protective devices can reduce thewetting of exposed end-grain.

caps. The metal is usually installed over the pile be-fore the cap is placed in position. The drift pin de-presses the sheet metal slightly as it is driven throughthe cap and into the piling and also creates a less-than-watertight hole in the metal. This results in afunneling of capillary water in the metal-to-cap in-terface to the piling wood around the driftpin hole.Nails through the metal into the pile top function inthe same way.

Similarly, metal caps on fender piles are generally in-effective; they invariably rupture because of mooringhausers, vandals, or other causes (Fig. 16). Watertrapped under the covering is slow to evaporate andadds to the decay hazard.

Bituminous or asphaltic mastics used as sealants orbedding compounds appear to be most effective forpreventing wetting in cracks and joints and throughwood end-grain (Fig. 17). As tightly adhering coat-ings, these mastics eliminate troublesome capillaryspaces common with membranes and sheet metal cov-ers. They may be applied appropriately as end-graincoatings, joint fillers or seals, and check-filling com-pounds, but only if the wood is no more than mod-erately wet or if avenues other than those sealed areavailable for drying. Care must be exercised in makingsuch repairs. In addition, the repairs must be main-tained to ensure a watertight coating or the problemmay be compounded by formation of water entrapmentareas under the coatings.

Mastics have the advantage of lower material and in-stallation costs than metal or membranes. Mechan-ically damaged or weathered and defective coatingsthat are exposed and accessible can be repaired simplyby adding more coating material. However, such ma-terials will probably be more appropriately applied aspreventive maintenance measures rather than solutionsto existing decay problems.

On structures provided with asphalt surfaces, breaks inthe surface may develop in service because of deck de-flections, improper bonding, or poor construction prac-tices (Fig. 8). When such breaks occur, they shouldbe repaired as soon as possible to prevent continuedand more serious deterioration. Cracking may resultfrom several causes but typically results from differ-ential deck deflections at panel joints or at memberends. When cracks appear, they should be thoroughlycleaned with a stiff brush and compressed air, andfilled with emulsion slurry of liquid asphalt mixed withsand. Where pavement is broken or missing, surround-ing pavement should be removed to a point where

surfacing is sound and the pavement is tightly bondedto the deck surface. For best results, the repaired areashould be square or rectangular with vertically cutsides. After the area is cleaned, a tack coat should beapplied to the deck surface and the area patched witha dense grade of asphalt compacted to the elevation ofthe surrounding surface.

In-Place Surface Preservative Treatment

The purpose of in-place or supplemental treatments isto prevent or arrest decay in existing structures. Suchtreatments can provide a safe, effective, and economi-cal method for extending the service life of waterfrontstructures. In-place treatments were seldom used inthe past, partly because decay was not detected untilit had become visible or a member had weakened orfailed to some degree. Early detection of decay by fre-quent and thorough inspections eliminates this prob-lem. Two types of in-place treatment are commonlyused: surface treatment and fumigants. Surface treat-ments are used to prevent infection of exposed wood,and fumigants are used to treat internal decay.

Although maximum protection against decay is pro-vided by pressure treating according to AmericanWood-Preservers’ Association standards, in-place sur-face treatments can reduce the incidence of decay in(1) newly installed, untreated wood, (2) untreatedwood exposed by weather checks or mechanical dam-age in poorly pressure-treated species such as Douglas-fir, and (3) untreated wood exposed when pressure-treated wood members are cut or drilled. This typeof treatment is effective when applied before decay isestablished. In-place surface treatment can be usedfor maintaining structures because of its ease of ap-plication and effectiveness as a toxic barrier to newinfection. However, the shallow penetration of surfacetreatments limits their effectiveness for established in-ternal decay; in these cases, fumigants are much moreeffective in arresting decay. Such treatments are notintended to substitute for pressure treatment of newwood.

In-place preservative treatments consist of various liq-uid or heavier grease-type preservative compounds.The wood surface should be thoroughly saturated withpreservative so that all cracks and creases are treated;however, care must be exercised not to apply excessiveamounts that spill or run off the surface. The effective-ness of surface treating depends on the thoroughnessof application, wood species, and moisture content ofthe wood at the time of treatment. Wet wood absorbsless preservative than dry wood during brush or spray

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treatments. This factor is significant in waterfront pentachlorophenol two or more times using a smallstructures because many areas that require treatment pressure sprayer (Table 1). Although pentachlorophe-are subject to wetting. Field tests show that surface nol was not effective on Southern Pine decks, FCAPtreatments in above-ground locations can effectively provided almost as much protection for the wood as itprevent decay for at least 20 years. For waterfront ap- did for Douglas-fir. Unlike pentachlorophenol, whichplications, treatments should be systematically reap- diffuses little after penetration, water-soluble FCAPplied at intervals of 5 to 10 years to ensure adequate moves into checks as they open, thereby protecting theprotection from decay. wood below the surface.

Decks

Surface treatment can substantially protect un-treated Douglas-fir decks but not Southern Pinedecks. Douglas-fir lumber is largely heartwood andhas higher natural durability than Southern Pine,which is mostly sapwood. In research tests, Douglas-fir decking was kept essentially free of decay in Mis-sissippi for as long as 19 years by flooding the uppersurface with fluor-chrome-arsenic-phenol (FCAP) or

Supplemental treatment of decking would ordinarilynot be warranted if the wood were pressure treated. InSouthern Pine, weather checks rarely expose untreatedwood; in pressure-treated Douglas-fir, weather checksdo expose untreated wood, but decay in checks is sel-dom a problem. The durability of Douglas-fir can beattributed to the natural decay resistance of the heart-wood and rapid drying of the shallow checks. Leachingof preservative into the checks may also contribute todurability.

Table 1—Decay of surface-treated Douglas-fir and Southern Pinedecks after 19 years of exposure in Mississippi

Wood andtreating solutiona

Treatment Number Units in decay class (no.)b

time of Average(year) units 0 40 60 80 100 rating

Douglas-firSodium penta, 5%

Sodium penta,5% + WR

Penta in mineralspirits, 5% + WR

FCAP, 4%

(Control)

Southern Pinec

Sodium penta, 5%Sodium penta + WRFCAP, 4%

(Control)

2-9 15 152,6 10 32-9 15 152,6 10 62-9 15 152,6 10 82-9 15 152,6 10 8

25 0

2-9 25 02-9 25 02-9 15 152,6 10 4

25 0

030400000

00020

010002020

00020

000000000

00020

0 03 480 00 160 00 120 00 12

25 100

25 10025 100

0 02 56

25 100

a Penta, pentachlorophenol; WR, water repellent; FCAP,fluor-chrome-arsenic-phenol.

b Decay rated from 0 to 100. A rating of 80 indicatessufficient decay to warrant deck plank replacement.

c Penta-treated and untreated Southern Pine deck planksfailed by year 7.

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Curbs, Chocks, and Wales

Checks play an important role in the development ofdecay in large pressure-treated Douglas-fir timberssuch as curbs, chocks, and wales. Decay may dif-fer markedly in checks of Douglas-fir curbs pressuretreated with pentachlorophenol or creosote comparedto curbs treated with FCAP. In research tests, curbstreated with pentachlorophenol or creosote were de-cayed at the base of deep checks after 4 and 10 years,respectively. In contrast, curbs treated with FCAPshowed no decay after 17 years. Thus, the service lifeof creosote- and pentachlorophenol-treated curbs withdeep checks may not be much longer than that of un-treated curbs. Although creosote curbs without check-ing have been reported to be free of decay for as longas 25 years, the lack of checking in these instances hasnot been explained.

The absence of decay in FCAP-treated Douglas-fircurbs with deep checks suggests a unique ability ofFCAP to protect untreated, interior wood exposedby deep checks when the wood is not in contact withsoil. One or more constituent chemicals apparentlyleach from treated to untreated wood in amounts suffi-cient to prevent infection by fungal spores. The outersurfaces of the wood are not decayed, indicating thatsufficient preservative remains to protect these areas.

For curbs with deep checks, liberal application ofpreservative with a brush can provide protection tountreated wood at the base of checks. However, treat-ment will be successful only if the preservative is in thechecks before fungal infection occurs. Moreover, treat-ment may need to be repeated occasionally as long asthe checks deepen.

Piles

Premature failure of marine piling because of internaldecay is a major problem, leading to costly repair andreplacement of the wood. The damage is particularlyserious in fender piles, which protect both the dock-ing vessel and the pier or wharf from possible impactdamage. In addition to preservative treatment, thedecay hazard can be minimized by separating curbsand wales from the deck by filler blocks. The blocksprevent the large water-trapping zone created whentimbers are in direct contact with the deck (Fig. 12).

For pile tops, most fungicidal treatments in combina-tion with an intact cap will offer long-term protectionagainst decay. The fungicide and cap must be applied

immediately after the piles are cut off. If treatment isdelayed, decay may penetrate deep into the piling, andthe fungicide will not be effective.

Pile-capping materials should be chosen for ease ofapplication, long-term flexibility, cleanliness aftersetting, and reasonable wear under docking stresses(e.g., hawser scrapings). Pile caps are commonly madefrom epoxy compounds, galvanized metal, bituminouscompounds, roofing felt, heavy plastic, and fiberglassmesh cloth in combination with a bituminous material(Fig. 16,17). Galvanized metal, roofing felts, and plas-tic sheets are not recommended for capping materialsbecause condensation or leaks can create ideal condi-tions for decay beneath the cap. Epoxy compoundsfail as moisture barriers because their inflexibility re-sults in early cracking of the caps. Moreover, epoxycompounds are costly and difficult to apply (must beapplied in a two-component system). Bituminous com-pounds have proved best as capping materials becauseof their low cost and ease of application and repair.

Because pile caps on working piers are often dam-aged or pulled off by hawsers, the pile top should betreated by flooding with a preservative before capping.A waterborne preservative, such as ammonium bifluo-ride or FCAP, is apparently the most effective. Thesechemicals remain inactive as long as the cap remainssound, but they are activated in the presence of mois-ture. The preservative can also provide protection evenwhen the pile cap remains intact. By penetrating thewood, the preservative can eliminate shallow decay be-low the surface caused by delay in covering the piletop.

Grease-type preservatives troweled onto the pile cutoffare also effective in preventing decay. The piling neednot be capped. However, such preservatives would notbe desirable in many situations because the slick piletop could result in accidents from slippage. The easeof application and cleanliness of waterborne preserva-tives make them preferable to oil-type preservatives.

Remedial Measures

Replacement

A member may need to be replaced when its residualstrength is found to be inadequate. Two aspects of re-placement deserve consideration. If extended service isanticipated, the replacement member should be pres-sure treated with an appropriate preservative and any

23

untreated wood exposed by cutting or boring thor-oughly surface-treated. Because the removed memberhad decayed when exposed to the existing conditions,all members adjacent to the removed member shouldbe checked for possible decay. Whether decay is sus-pected or confirmed, the in-place members should becopiously flooded with preservative before the newmember is installed.

For practicality, only the defective part of a membermay sometimes be removed and replaced. In suchcases, the described recommendations for treatmentof the replacement member apply. If the wetting thatcaused decay cannot be prevented, an adequate lengthof the defective material must be removed to ensurethat the infected wood has been removed. Fungal in-fection may extend several inches in the grain directionbeyond the visible limits of the decay. A rule of thumbin removing decayed parts of members is to include thevisible decay plus an additional 2 ft (0.60 m) of adja-cent wood in the grain direction. The newly exposed,cutoff face of the old member as well as the replace-ment member should be treated with preservative inplace.

Reinforcement

When replacing a decayed member or part of a mem-ber is impractical (the replacement member cannot beeasily fitted into the structure), a sister member or re-inforcing element may be used to establish the neededload-carrying capacity. Where feasible, the old mem-ber or its defective part should be removed as a guardagainst spread of the decay into the new, contactingmembers.

As with replacement members, reinforcing membersshould be pressure treated, and any wood exposed bycutting or boring should be surface treated.

Fumigant Treatment

Despite pressure treatment with a preservative, largetimbers such as curbs, chocks, and wales can developinternal decay through deep checks that penetrate thetreated shell; decay can also enter piles through cutoffends (Figs. 11,15). The problem is most serious withshallow-treated species such as Douglas-fir. Preser-vatives applied by ordinary flooding from a brush orspray only slightly penetrate the wood and so cannotstop decay.

Fortunately, a type of preservative has been developedthat can move through and permeate wood that can-not be conventionally treated. The chemical, whichmigrates as a gas and is called a fumigant, offers awidely useful means for eliminating deep-seated de-cay. Fumigants can effectively supplement conventionalpreservatives because they can be introduced at thetreatment plant.

Fumigants are applied in liquid or solid form inpredrilled holes; they then volatilize into a toxic gasthat moves through the wood, eliminating decayfungi and insects. Fumigants can diffuse in the di-rection of the wood grain for over 8 ft (2.4 m) frompoint of application in poles. Commonly used liq-uid fumigants are Vapam (33 percent sodium N-methyldithiocarbiamate), Vorlex (20 percent meth-lisothiocyanate, 80 percent C-3 hydrocarbons), andchloropicrin (trichloro-nitromethane). All three areregistered with the Environmental Protection Agencyfor application to wood products. Solid chloropicrinand 100 percent methylisothiocyanate (MIT) are avail-able in capsules or glass tubes. Solid fumigants pro-vide increased protection against decay, reduce riskof environmental contamination, and can be used inpreviously restricted applications.

Like nearly all other pesticides and preservatives,fumigants are toxic to humans and must be handledproperly. They should be handled by only trainedpersonnel who fully understand necessary precautionsand should be applied in accordance with State andFederal laws.

To be most effective, a fumigant should be applied atlocations where it will not leak away or be lost by dif-fusion to the atmosphere. When fumigants are applied,the timbers should be inspected thoroughly to deter-mine an optimal drilling pattern that avoids metal fas-teners, seasoning checks, and severely rotted wood.

In vertical members such as piles, holes to receive liq-uid fumigant should be drilled at a steep angle (145°to 60°) downward toward the center of the member,avoiding crossing of seasoning checks. The holes shouldbe no more than 4 ft (1.22 m) apart and arranged ina spiral pattern. With horizontal timbers, the holescan be drilled straight down or slanted; slanting is gen-erally preferable because it prevents a larger surfacearea in the holes for escape of fumigant. As a rule,the holes should be extended to within about 2 in.(5.08 cm) of the bottom of the timber. If strength isnot jeopardized, holes can be drilled in a cluster or in

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pairs to accommodate the required amount of preser-vative. If large seasoning checks are present, the holesshould be drilled on each side of the member to pro-vide better distribution of fumigant (Fig. 24). Herealso, treatment holes should be no more than 4 ft(1.22 m) apart. If fumigant leaks from a hole, the holeshould be plugged; another hole should be drilled intosound wood or away from the check, if a check is theproblem. As soon as the fumigant is injected, the holeshould be plugged with a tight-fitting treated wooddowel, driven slowly to avoid splitting the wood. Forliquid fumigants, sufficient room must remain in thetreating hole so the plug can be driven without squirt-ing the chemical out of the hole. The amount of fu-migant needed and the size and number of treatingholes required depend on timber size. Liquid fumi-gants can be applied from l-pint (0.53-1) polyethylenesqueeze bottles, transferring the liquid from 5-gallon(21.1-1) stock containers to the bottles by suitablyarranged tubing. Stock solution in a cylinder is some-times dispersed to the wood directly from the cylin-der. Licensed commercial fumigant treaters, followingthese guidelines, can be helpful in seeing that the fu-migants are introduced appropriately and safely. Alist of such treaters is available from the USDA ForestService, Forest Products Laboratory, Madison, Wiscon-sin, and the Forest Research Laboratory, Oregon StateUniversity, Corvallis, Oregon.

Fumigants will eventually diffuse out of the wood,allowing decay fungi to recolonize. In ongoing trialson utility poles, Vorlex and chloropicrin have remainedeffective for as long as 15 years; duration of protectionby Vapam has been somewhat less. In creosoted

waterfront curbing, chloropicrin remained effectivefor at least 10 years whereas Vapam-treated timbersneeded retreatment in about 5 years. Shorter peri-ods of protection can be expected if the fumigants areinjected close to fastener holes, splits, checks, or endgrain, where the chemical can be more easily lost bydiffusion to the atmosphere. When inspections detectthe presence of active fungi, protection by the fumi-gant has declined sufficiently to warrant retreatment.One attraction of fumigant treating is that the woodcan be retreated at periodical intervals in the sameholes used for the initial treatment. The old plug isdrilled or pulled, the new fumigant is added, and thehole is replugged with a new treated dowel.

Precautions

All wood preservatives and fumigants are toxic to hu-mans. Therefore, special care is needed for in-placetreatment and the products must be used in accor-dance with State and Federal laws. Environmental andhealth hazards are minimal when treatments are ap-plied properly. The potential for environmental dam-age is higher in field locations because of variable con-ditions and the proximity to streams and other watersources. In-place treatments must be applied only bytrained and licensed personnel who fully understandhow to apply the treatments and what safeguards toemploy. Those responsible for in-place treating shouldobserve the following precautions.

1. Avoid breathing preservative dusts or sprays, andavoid bodily contact with preservative.

Figure 24—Deep seasoning checks can penetrate the shell of large pressure-treatedexterior timbers. A, Internal decay caused by water trapped in checks. B, Pluggedholes in timbers. Fumigant applied through holes stopped internal decay. Note thattreating holes are located on both sides of deep checks.

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2. Wear protective gloves and aprons when treatinglumber or when handling lumber wet with treatingsolution.

3. Wash inside of gloves with water frequently.

4. Wash hands and other skin areas wetted by preser-vative with soap and water immediately.

5. Watch for special sensitivity to preservative, espe-cially in persons using the preservative for the firsttime. Those who showing skin sensitivity shoulddiscontinue using the preservative.

6. Have a respirator or gas mask available when apply-ing fumigants under adverse weather conditions.

In general, in-place treatment by local maintenancecrews is limited by the scope of the treatment re-quired. For routine maintenance, the amount of treat-ment required is usually minor, and local crews can beused when properly trained and licensed. For largerprojects involving many timber members or an entirestructure, the project should be contracted to licensedspecialists in the field. Some companies have providedin-place treating services for many years and have ex-cellent safety records. When selecting a contractor,records of previous experience and performance his-tory should be carefully evaluated to ensure that thecontractor is qualified for the job. Assistance in lo-cating contractors may be obtained from treatingorganizations or from chemical manufacturers.

References

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U.S. GOVERNMENT PRINTING OFFICE: 1989/643-043/00010