To give yourself the greatest number of decoratingoptions in the future, paint the finished drywall surfacewith a coat of flat oil-base primer. Whether you intendto wallpaper or paint with latex, oil-base primer adheresbest to the facing of the paper and seals it.Renovation and RepairFor the best results, drywall should be flat againstthe surface to which it is being attached. How flat thenailing surface must be depends upon the desired finisheffect. Smooth painted surfaces with spotlights on themrequire as nearly flawless a finish as you can attain.Similarly, delicate wall coverings-particularly thosewith close, regular patterns—accentuate pocks andlumps underneath. Textured surfaces are much moreforgiving. In general, if adjacent nailing elements (studs,and so forth) vary by more than 1/4 inch, buildup lowspots. Essentially, there are three ways to create a flatnailing surface:Frame out a new wall-a radical solution. If thestuds of partition walls are buckled and warped,it’s often easier to rip the walls out and replacethem. Where the irregular surface is a load-bearing wall, it maybe easier to build a new wallwithin the old.Cover imperfections with a layer of 3/8-inchdrywall. This thickness is flexible yet strong.Drywall of 1/4-inch thickness may suffice.Single-ply cover-up is a common renovationstrategy where existing walls are ungainly butbasically flat. Locate studs beforehand and usescrews long enough to penetrate studs and joistsat least 5/8 inch.Build up the surface by “furring out.” In theFigure 5-12.—Furring strips hacked with shims.the center of each stud on the existing surface. Here too,mark the depth of low spots.The objective of this process is a flat plane of furringstrips over existing studs. Tack the strips in place andadd shims (wood shingles are best) at each low spotmarked (see fig. 5-12). To make sure a furring stripdoesn’t skew, use two shims, with their thin endsreversed, at each point. Tack the shims in place andplumb the furring strips again. When you are satisfied,drive the nails or screws all the way in.“furring- out” procedure, furring-strips 1 by 2inches are used. Some drywall manufacturers,however, consider that size too light forattachment, favoring instead a nominal size of 2by 2 inches. Whatever size strips you use, makesure they (and the shims underneath) areanchored solidly to the wall behind.By stretching strings taut between diagonal comers,you can get a quick idea of any irregularities in a wall.If studs are exposed, further assess the situation with alevel held against a straight 2 by 4. Hold the straightedgeplumb in front of each stud and mark low spots every12 inches or so. Using a builder’s crayon, write the depthof each low spot, relative to the straightedge, on the stud.If studs aren’t exposed, locate each stud by test drillingand inserting a bent coat hanger into the hole. Chalk lineWhen attaching the finish sheets, use screws or nailslong enough to penetrate through furring strips and intothe studs behind. Strips directly over studs ensure thestrongest attachment. Where finish materials are notsheets—for example, single-board vertical paneling—furring should run perpendicular to the studs.Regardless of type, finish material must be backedfirmly at all nailing pints, corners, and seams. Whereyou cover existing finish surfaces or otherwise alter thethickness of walls, it’s usually necessary to build upexisting trim. Figure 5-13 shows how this might be doneFigure 5-13.—Building up an intertor window casing.5-11
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