60 WALLS & CEILINGS • May 2004

All Things Gypsum

By Michael Gardner

Repair and Painting of Gypsum BoardAuthor’s Note: A portion of this month’s columndiscusses touching up existing paint after a gyp-sum wallboard repair. The information is pre-sented so that the drywall contractor will have abetter understanding of how paint may work, inthe hope that the knowledge may be of assistanceon a future project. Presenting the information isnot meant to suggest that the Gypsum Asso-ciation is broadening its scope of expertise,and it does not in any wayintend to encourage thereader to use us as aresource regarding theproper application ofpaint. For information onpaint application andpainting techniques, readersshould contact the technicalservices department of the paintmanufacturer.

An occasional problem encountered after fin-ishing gypsum board, particularly wheninstalled over lumber that has not been allowedto stabilize, and/or in the winter months whenthe temperature and humidity rise and fallrepeatedly, is “joint ridging” or “beading.” Jointridging appears as a uniform line or bead(hence the term “beading”) that runs along thejoint where the edges of two gypsum boardpanels meet. One cause of the ridge or bead isexcessive compression on the edges of the twopanels, forcing the edges to swell out. Anothercause is the result of butting a tapered edge upto a squared edge without sufficient joint treat-ment. Yet another cause is misaligned framingbehind the joint, either due to improper instal-lation of the framing or twisting of the wood,due to temperature and humidity fluctuations,which forces the edges of the two boards tomove out of alignment.

Repairing this condition is usually a rela-tively simple procedure. First, the buildingmust be allowed to stabilize, meaning that theexpanding and contracting of the buildingmaterials as they release or absorb moisture

must run its course. This process generallyrequires one complete temperature cycle,depending upon the location of the building.

StabilityOnce the building is stable, ridged jointsshould be sanded down closer to the plane of

the wall or ceiling surface. One shoulduse care not to sand too deeply and

damage the embedded joint rein-forcing tape. After the ridge is

sanded down, any voids inthe joint should be filledwith either topping com-pound or all-purpose jointcompound, spreading and

feathering the compound outwide enough so that the sur-

face appears flat. Allow thecompound to dry at least 24

hours, and then sand it to smooth out the sur-face and remove any tool marks. If necessary,add additional layers of compound, allowingeach coat 24 hours to dry before sanding.

Joint ridging is most often noticed, and cor-rected, after the surface has been prime or finishpainted. Occasionally, a walk-through of a jobsite will reveal painted walls, and sometimesceilings, that have stripes of freshly applied jointcompound marking a few gypsum board joints.Obviously, such joints will need to be repaintedto match the existing paint. But before therepaired joint can be painted or otherwise deco-rated, it should be primed with a primer appro-priate for the desired decoration. In someinstances, this will be a high quality latex dry-wall primer, but one should never assume thatthe final decoration will be compatible with justany primer—always read the labels beforeapplying a primer and a finish.

This takes us to the larger topic of paintingnew gypsum board and painting repaired gyp-sum board areas. There are several grades ofinterior paint offered by most paint manufac-turers, usually at least a “good,” “better” and“best line,” and frequently a “not-so-good” and

“”Proper repair ofgypsum board

surfaces requires a bit of a defttouch and an

understanding ofexactly howpaints andprimers are

impacted by lightand the surface to

which they are applied.

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WALLS & CEILINGS • May 2004 61

a premium line, as well. Each manufacturer will have specificrecommendations for each of these lines of paint, includingpreparation, priming, application and touch-up. Often, a fin-ish paint is sold as self-priming, meaning that multiple coats ofthe same material are intended to be used over the substrate toachieve the desired look. Sometimes such a paint may be usedwith a primer, and sometimes it is best not to.

Before painting or decorating a gypsum board surface, itmust be finished to the appropriate level, as described ineither Gypsum Association publication “GA-214, Recom-mended Levels of Gypsum Board Finish,” or in ASTM C 840,“Standard Specification for Application and Finishing of Gyp-sum Board.” For most interior paint finishes, either a Level 4or 5 gypsum board finish is appropriate. Level 4 requires thatall joints are first taped by embedding joint tape in a layer ofjoint compound and then are given another two layers of jointcompound, and that all fastener heads and accessories are giv-en three separate coats of joint compound. Level 5 requiresthat a skim coat of joint compound or a material manufac-tured to specifically function as a skim coat be applied to theentire gypsum board surface once Level 4 has been achieved.

Level 4 gypsum board finish is appropriate for truly flatpaints. Most “builder grade” paints fit this category and areoften designed to be self-priming. These “no sheen” paints typi-cally use coarsely ground pigments that impart texture to the

paint film. This texture facilitates easy touch-up and masksminor surface irregularities that are more apparent under severelighting conditions when paint with a higher sheen is used.

Level 5 gypsum board finish is recommended for any sur-face that will be decorated with a paint that exhibits a sheenor gloss, or with a non-textured flat paint. Most premiumquality flat paints exhibit some angular sheen and are consid-ered non-textured. These premium flat paints typically usemore finely ground pigments that impart no significant tex-ture to the paint film. A Level 5 finish is required for thesepaints, because the skim coat provides the necessary porosityand profile to the surface for it to appear uniform in textureand color once painted with a paint that has any degree ofsheen. Level 5 should also be used in areas with severe light-ing conditions that are likely to highlight any surface irregu-larity, regardless of the paint used.

In other words, if a gypsum board surface is finished to Lev-el 4—that is taped joints and compound on the fasteners andaccessories but no skim coat—and a paint with an angularsheen (i.e., a non-textured flat paint) is applied, the paper areaswith no joint compound over them may have a different texturethan those areas covered with joint compound. If a non-tex-tured flat paint is applied, the color on the areas covered withjoint compound may appear different (lighter from one direc-tion, darker from the other) than the non-covered areas. This is

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62 WALLS & CEILINGS • May 2004

because light is reflected differently by the areas that are cov-ered with compound, as opposed to those that are not.

Complicated processThis whole process becomes slightly more complicated whenthe repair of a gypsum board surface occurs after the paint hasbeen applied. In the best of all possible worlds, the original paintis a couple of coats of the self-priming flat that is commonlyused in new home construction. If the original batch of paint isavailable, a couple of coats of this paint applied directly over therepaired joint may enable the repair to just fade into the wallonce dry. If a different batch is used, it may be necessary torecoat the entire surface to achieve a uniform appearance.

In the instance when self-priming paint was used exclusive-ly, applying a high-solids premium latex primer over therepaired area and then attempting to touch-up with buildergrade paint may prove to be counter-productive. Because theresin solids in the paint are “held out” by the primer and arenot absorbed by the primed surface at the same rate as the adja-cent painted wall, the surrounding non-repaired and paintedsurface is more absorbent than the primed/patched area. Thismay cause a coat of paint over the primed surface to appearslightly lighter in color than the surrounding non-repairedarea. Additional resin solids at the surface of the paint film canalso raise the sheen just enough to make the repair visible.

The use of most high quality or premium paints will likelynecessitate repainting the entire surface after a joint repair.Successful touch-up is improbable because the areas where theprimer and the touch-up paint overlap the existing paint willhave twice the film thickness of the patched area. This oftenlooks like a halo around the repair, due to both a sheen and aprofile difference. Usually, the patched area can be primedwith the compatible primer and then the whole surface recoat-ed with the finish paint; however, if the size of the project isconsiderable, it is best to do a test of the whole system first toensure that the desired result is achieved on the first attempt.Otherwise, it may be necessary to sand and prime the entiresurface before repainting to achieve an even appearance.

Proper repair of gypsum board surfaces requires a bit of adeft touch and an understanding of exactly how paints andprimers are impacted by light and the surface to which theyare applied. One’s best effort at correctly patching a damagedgypsum board surface can be undone by the unwillingness ofa paint applicator to patiently and correctly apply therequired type of paint. W&C

Michael Gardner is the executive director of the Gypsum Association, aninternational trade association representing gypsum board manufacturersin the United States and Canada.

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