Wood Siding–Installing, Finishing,Maintaining

United StatesDepartment ofAgriculture

PREPARED BY Home and GardenForest Service Bulletin 203

Contents

PageIntroduction . . . . . . . . . . . . . . . . 3Types of Wood Siding. . . . . . . . 4

Lumber. . . . . . . . . . . . . . . . . . 4Plywood . . . . . . . . . . . . . . . . . 6Reconstituted Wood Products 7

Selecting Wood Siding. . . . . . . 8Installing Wood Siding. . . . . . . 8

Horizontal Siding. . . . . . . . . . 8Plywood and Other SheetSiding. . . . . . . . . . . . . . . . . . . 10Shingles and Shakes. . . . . . . . 11

The House and Moisture. . . . . . 12Types of Wood Finishes. . . . . . 14

Paint. . . . . . . . . . . . . . . . . . . . 14Solid-Color Stains. . . . . . . . . . . I5Semitransparent PenetratingStains . . . . . . . . . . . . . . . . . . . 15Water-Repellent Preservatives. 15Varnishes . . . . . . . . . . . . . . . . 17Preservatives. . . . . . . . . . . . . . 17

Applying Wood Finishes. . . . . . 18Paint. . . . . . . . . . . . . . . . . . . . 18Additional Tips on Painting. . 19Solid-Color Stains. . . . . . . . . .20Semitransparent PenetratingStains . . . . . . . . . . . . . . . . . . . 20Water-Repellent Preservatives. 21

Refinishing. . . . . . . . . . . . . . . . . 22Paint . . . . . . . . . . . . . . . . . . . . 22Solid-Color Stains. . . . . . . . . . 22Semitransparent PenetratingStains . . . . . . . . . . . . . . . . . . . 22Water-Repellent Preservatives. 22

Warnings. . . . . . . . . . . . . . . . . . 23

Revised December 1983

Wood Siding— Installing,Finishing, Maintaining

by W. C. Feist and A. E. Oviatt1

Introduction

Wood siding is put on houses formany good reasons.

One reason is that it will keep thebright new “face” of any home at-tractive for many years to come. Infact, given reasonable care, woodsiding will retain its beauty for cen-turies, as has been amply proved byits performance on houses that dateback to early colonial times. It alsohas great versatility; and the largevariety of patterns, sizes, and colorsallows for effects ranging from thesimple charm of colonial clapboardto the rustic beauty of board-and-batten and rough-textured plywoodor lumber siding. In between aremany other varieties and combina-tions that produce distinctive andattractive effects.

Then there is the ease and speedwith which it can be sawed, fitted,

1Chemist and Forest Products Technol-ogist (Retired), USDA Forest Service,Forest Products Laboratory, Madison,Wis. The laboratory is maintained incooperation with the University ofWisconsin.

and nailed into place. Otherreasons are its fuel-saving value,because of the millions of tinyhollow fibers that make it a goodinsulator, and its natural resistanceto the ravages of weather.

Other reasons to use wood sidinginclude its ability to hold a widevariety of finishes-clear ones thatreveal and accentuate its naturalbeauty, stains that impart a rusticappearance, and paints of everyconceivable color. Within limits,the color scheme can be changedperiodically to give a home a freshnew appearance in keeping withchanging times. It is little wonderthat wood siding has come to standfor warmth, comfort, security,beauty-all the things that spell“home.”

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Types of Wood Siding

Many kinds of wood siding areon the market today. All will givegood service, provided each is usedproperly.

There are three general categoriesof wood siding commonly used inconstruction. These are lumber,plywood, and reconstituted woodproducts such as hardboard andparticleboard. Each product hasunique characteristics that will affectthe durability of any finish appliedto it.

lumber

Lumber is being used less and‘less as exterior siding, but was oncethe most common wood materialused in construction. Many olderhomes have wood siding. The abil-ity of lumber to retain and hold afinish is affected by species, bygrain direction or how the piecewas sawn, and by smoothness.

The weight of wood varies greatlybetween species. Some commonconstruction woods such assouthern yellow pine are dense and

heavy compared to the lighterweight ones such as redwood andcedar. The weight of wood is im-portant because heavy woods shrinkand swell more than light ones.This dimensional change in lumberoccurs as the wood gains or losesmoisture. Wood in heated homestends to dry and shrink in thewinter and gains moisture andswells in the warm summer months.Excessive dimensional change inwood consistently stresses a paintfilm and may result in early failure.

Some species have wide bands ofdark, dense wood alternating withbands of light, softer wood. Thelight bands are formed in the springof the year and are calledearlywood. The dark bands areformed in the summer and are call-ed latewood (fig. 1). Bands oflatewood are characteristic ofsouthern yellow pine and someboards of Douglas-fir. Paint will nothold well on these species, andpenetrating stains are preferred. Onthe other hand, wide latewood

Figure 1–Earlywood and latewoodbands in southern yellow pine. Thesedistinct bands often lead to early paintfailure. Therefore, penetrating stains arepreferred. M830023

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bands are not characteristic of red-wood and cedar; therefore, thesespecies are recommended whenpaint will be used.

Grain direction also affects paint-holding characteristics and is deter-mined at the time lumber is cutfrom a log. Lumber is referred to asflat-grained, edge-grained (quarter-sawed), or a combination of thetwo (fig. 2). Most standard lumbercontains a high percentage of flatgrain.

Lumber used for board-and-battensiding, drop siding, or shiplap is fre-quently flat-grained. Bevel siding ofredwood or cedar is often, but notalways, manufactured so that it isedge-grained. Edge-grained bevelsiding will hold paint well. Flat-grained lumber will not hold paintas well since it shrinks and swellsmore than edge-grained lumber andbecause wide, dark bands oflatewood are frequently present(fig. 3).

Paint will last longer on smooth,edge-grained surfaces. Penetratingstains or preservative treatments arepreferred for rough-sawn lumber.These treatments often accentuatethe natural or rustic look of rough-sawn lumber and allow the woodgrain and surface texture to showthrough the finish.

For houses, bevel siding isperhaps the most widely used. (Seefig. 7.) Drop siding and shiplap pat-terns are also used, especially onbuildings without sheathing. Thesepatterns of siding are appliedhorizontally and tend to make ahouse appear lower and longer.

Vertical siding is increasinglypopular. It consists of tongued-and-grooved boards or squareedgedboards applied vertically, often withnarrow strips called battens nailedover the joints. Vertical patternswith smooth and rough-sawn sur-faces are available in plywood ofDouglas-fir, redwood, and western

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Figure 2–Edge-grained (or quarter-sawed) board (left) and flat-grained (orplainsawed) board (right) cut from a log.M147253

Figure 3–Paint applied over edgegrained boards (top and bottom) per-forms better than that applied to flat-grained boards (middle). M147211-7

redcedar. Vertical siding tends tomake a house appear taller.

Plywood

Exterior plywood with a rough-sawn surface is commonly used forsiding. Smooth-sanded plywood isnot recommended for siding, but itmay be used in soffits. Both sandedand rough-sawn plywood candevelop surface checks, especiallywhen exposed to moisture andsunlight. These surface checks canlead to early paint failure with oilor alkyd paint systems (fig. 4).Quality acrylic latex paint systemsgenerally perform better.

The flat-grained pattern present innearly all plywood can also con-tribute to early paint failure.Therefore, if smooth or rough-sawnplywood is to be painted, specialprecautions should be taken.Penetrating stains are often moreappropriate for smooth-sanded andespecially rough-sawn exteriorplywood surfaces.

Plywood manufactured with amediumdensity paper overlay is fre-quently called MDO. Compared tostandard rough-sawn or smoothplywood, MDO holds paint well.MDO plywood is not always astock item in many lumber yards,but it can usually be ordered.

Figure 4–Early paint failure onplywood because of penetration ofmoisture into surface checks ofplywood. M830013-6

Reconstituted Wood Products

Reconstituted wood products arethose made by forming small piecesof wood into large sheets, usually 4by 8 feet, or as required for aspecialized use such as beveleddrop siding. These products may beclassified as fiberboard or par-ticleboard, depending upon thenature of the basic woodcomponent.

Fiberboards are produced frommechanical pulps. Hardboard is arelatively heavy type of fiberboardand is used for exterior siding. It isoften used as a substitute for bev-

eled drop siding, traditionally madefrom solid wood.

Particleboards are manufacturedfrom whole wood in the form ofsplinters, chips, flakes, or shavings.Waferboard and flakeboard are twotypes of particleboard made fromrelatively large flakes or shavings.

Only some fiberboards and par-ticleboards are manufactured for ex-terior use. Film-forming finishessuch as paints and solid-color stainswill give the most protection tothese reconstituted wood products.Some reconstituted wood productsare factory primed with paint andsome even have a top coat.

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Selecting Wood Siding

The kind of siding chosen will de-pend on where the house is built,its price range, and the architecturaleffect wanted. A range of quality inlumber and wood-based panel pro-ducts is available from clear,smooth edge-grained to rough, flat-grained with knots. These and othervisual characteristics should begiven special finishing treatments inaccord with the effects wanted.

Many species of wood can beused for siding. In siding cut fromlumber, medium decay resistance,freedom from warping, lowshrinkage, easy working qualities,and good finishing characteristicsare desirable.

Among the species with all ormost of these qualities are thecedars, redwood, the white pines,the spruces, and yellow-poplar.Douglas-fir and the southern pinesare also used in the better clear

dense hardwoods hgrades. Thevery limited local use.

Instal l ing Wood Siding

Horizontal Siding

Wood siding is simple to install.It is precision manufactured tostandard sizes and is easily cut, fit-ted, and fixed in place with or-dinary tools.

Courses of horizontal sidingshould be spaced so that a singleboard runs continuously above andbelow windows and above doorswithout notching: Bevel siding thatis 6 inches wide should have atleast 1 inch of overlap betweencourses. Siding that is 8 inches orwider should overlap 1 to 1½inches, depending on spacing re-quired between window heights(fig. 5).

Figure S-Installation of bevelML835110

siding.

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Siding should be butted snuglyand squarely against door and win-dow casings, corner boards, and ad-joining boards. (Corner boardsshould lie flat against thesheathing.) If metal corner coversare used, siding boards should becarefully cut to avoid leaving ahollow place under the cornercover where water could collect

A

(fig. 6). Mitered corners should beprecisely fitted for the same reason.

To fasten siding in place, zinc-coated, aluminum, or other noncor-rosive nails are recommended. Plainsteel-wire nails, especially the large-headed type that are designed forflush driving, make unsightly rustspots on most paints. Even small-headed plain steel nails, counter-

Figure 6–Recommended proceduresfor corners of siding: (A) Miter corners,(B) metal corners, (C) corner boards, and(D) interior corner. M134776

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sunk and puttied, are likely to spotthe finish with rust. Naturally fin-ished siding is installed best withaluminum or stainless steel nails.

For best performance, nailing pat-terns for the various kinds of sidingare very important and should com-ply with the recommendations ofthe manufacturers (fig. 7).

Plywood and Other Sheet Siding

Exterior-grade plywood, paper-overlaid plywood, and similar sheetmaterials used for siding are usually

applied vertically. When used oversheathing, plywood should be atleast 1/4 inch thick, although 5/16and 3/8 inch will normally providea more even surface. Hardboardshould be l/4-inch thick andmaterials such as mediumdensityfiberboard should be l/2-inch thick.

All nailing should be over studs,and total effective penetration intowood should be at least l-1/2inches. For example, 3/8-inchplywood siding over 3/4-inch woodsheathing would require about asevenpenny nail, which is 2-1/4

Figure 7–Patterns of wood siding andrecommended nailing practices: (A)Horizontal application, and (B) verticalapplication. M139819

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inches long. This would result in a1-1/8 inch penetration into the stud,but a total effective penetration of1-7/8 inches into wood.

Plywood should be nailed at6-inch intervals around theperimeter and at 12-inch intervals inthe middle. Hardboard sidingshould be nailed at 4- and 8-inchintervals. All types of sheet materialshould have a joint caulked withmastic unless the joints are of theinterlapping or matched type or bat-tens are installed. Putting a strip of15-pound asphalt felt under un-caulked joints is good practice.

Shingles and Shakes

Wood shingles and shakes havealso been used as siding since col-onial times, and remain popular on

colonial and Cape Cod styles aswell as more contemporary designs.They may be applied in single- ordouble-course patterns. It is per-missible for singlecourses to have alarger exposure on sidewalls thanon roofs, as the vertical pitch per-mits faster drainage and reduceswind-blown penetration of water.Headlap (the amount of lap overthe second course below) may beas little as 1 inch (fig. 8).

Doublecourse application resultsin deeper shadow lines at the dou-ble butts. The first course may be oflower quality such as grade 3; butthe top course should be grade 1,since much of the shingle or shakeis exposed (fig. 9).

Some wood-based panel productshave simulated shingle appearancesor have premounted shingles on abacking panel.

Figure 8–Single-coursing of sidewalls(wood shingles or shakes). M134610

Figure 9–Double-coursing ofsidewalls (wood shingles or shakes).Ml34609

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The House and Moisture

Wood siding is a part of thehouse; therefore, its performance isvitally affected by the rest of thestructure. The whole house must beproperly built to insure long-lastingservice.

Insulation, weatherstripping, andgenerally tight construction reducefuel bills and make for comfort, buttheir misuse may create some paintproblems.

Water vapor formed within ahouse moves through the inner sur-faces of the outer walls because ofdifferences in temperature betweenthe inside and outside. This watervapor condenses and collects as

water or frost in the siding duringthe winter. With the return of warmweather in the spring, this moisturecan-and often does-cause the ex-terior paint to blister. The problemhas been further accentuated by airconditioning and by humidifying.

A number of measures can betaken to help keep moisture out ofwalls. One of the most effective isto put a good vapor barrier underthe plaster, drywall, or paneling.Asphaltcoated paper, aluminumfoil, and polyethylene film aresatisfactory vapor barriers for homes(fig. 10).

Figure 10–Vapor barrier (on warmside of wall) has prevented moisturefrom getting into walls. ML835109

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Rain and snow water must bekept out, too. Roof gutters must be

and attic spaces ventilated so heatlosses do not melt snow on roofs to

sloped and have enough down-spouts or they may overflow during

produce ice dams and clog gutters(fig. 11).

rainstorms and let water seep intowalls through joints in the siding.

Wide roof overhangs help in

Attic floors should be well insulatedkeeping moisture out. So, too, doesmetal flashing in roof valleys, along

Figure 11–Ice dams: (A) Insufficientinsulation and ventilation can cause icedams and water damage; and (B) Goodventilation, insulation, and roof flashingminimize problems. M134787

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Types of Wood Finishes

dormers, and around chimneys(fig. 12). Window and door framesalso need adequate cap flashing.

A comparatively simple treatmentfor siding helps keep water out ofwood. Siding can be dipped in awater-repellent preservative before itis installed or the water-repellentpreservative can be brushed on afterthe siding is installed, but before itis painted. These preservatives aresold by lumber dealers and somepaint stores. They containfungicides, resins, and waxes (waterrepellent) that cause water to runoff instead of penetrating into thewood at end and lap joints.

Paint

Paints are common coatings usedon wood and provide the most pro-tection. They come in a wide rangeof colors and may be either oil orlatex based. Latex-base paints andstains are water borne, and oil oralkyd paints are solvent borne.Paints are used for decorative pur-poses, to protect the wood surfacefrom weathering, and to concealcertain defects.

Paints are applied to the woodsurface and do not penetrate itdeeply. The wood grain is com-pletely obscured, and a surface film

Figure 12–Metal flashing alongdormers helps keep moisture out ofsiding; the flashing extends back ofsiding and under shingles. ML835330

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is formed. This surface film canblister or peel if the wood is wettedor if inside water vapor movesthrough the house wall and woodsiding because of the absence of avapor barrier or one that isdefective.

Latex-base paints are generallyeasier to use since water is used incleanup. They are also porous and,thus, will allow some moisturemovement. In comparison, oil-basepaints require organic solvents forcleanup, and some are resistant tomoisture movement.

Paints perform best on smooth,edge-grained lumber of lightweightspecies such as redwood and cedarand on hardboard and overlaidplywood. Paints are the only way toachieve a bright white finish.However, they are subject to peel-ing where moisture is a problem.Paint is best for smooth surfaces;stains and preservatives, for roughsurfaces.

Solid-Color Stains

Solidcolor stains, also calledheavy-bodied stains, are opaquefinishes, which come in a widerange of colors and are defined asstains. Solidcolor stains are madewith a much higher concentrationof pigment than the semitransparentpenetrating stains described below.As a result, they will obscure thenatural wood color and grain. Oil-base solidcolor stains tend to forma film much like paint, and as aresult, can also peel loose from thesubstrate. Latex-base solid-colorstains are also available and form afilm as do the oil-base solid-colorstains. These stains are similar tothinned paints.

Semitransparent Penetrating Stains

Semitransparent penetrating stainsare popular for rustic finishes. Theyare moderately pigmented and thusdo not totally hide the wood grain.These stains penetrate the woodsurface, are porous, and do notform a surface film like paint. As aresult, they will not blister or peeleven if moisture gets into the wood.Penetrating stains are alkyd or oilbased and usually contain afungicide or water repellant. Latex-base (waterborne) stains are alsoavailable, but they do not penetratethe wood surface as do the oil-basestains.

Stains are most effective on roughlumber or plywood surfaces, butthey also provide satisfactory perfor-mance on smooth surfaces. Theyare available in a variety of colorsand are especially popular in thebrown tones since they give anatural or rustic wood appearance.They are not available in white.They are also an excellent finish forweathered wood. They are not ef-fective when applied over a solid-color stain or over old paint and arenot recommended on hardboard orsimilar reconstituted wood panelproducts.

Water-Repellent Preservatives

A water-repellent preservativemay be used as a natural finish. Itcontains a fungicide (usually pen-tachlorophenol or coppernaphthenate), a small amount ofwax as a water repellant, a resin ordrying oil, and a solvent such asturpentine or mineral spirits. Water-repellent preservatives do not con-tain any coloring pigments.

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Therefore, the resulting finish willvary in color depending upon thekind of wood.

Water-repellent preservatives mayalso be used as a treatment for barewood before priming and paintingor in areas where old paint haspeeled, exposing bare wood, par-ticularly around butt joints or incorners. This treatment keeps rainor dew from penetrating into thewood, especially at joints and endgrain, and thus decreases the shrink-ing and swelling of wood. As aresult, less stress is placed on thepaint film, and its service life is ex-tended (fig. 13). This stability isachieved by the small amount ofwax present in water-repellentpreservatives. When dip treated, thewax also decreases the capillarymovement of water up the backside of lap or drop siding. The

AFigure 13–(A) Window sash and

frame treated with a water-repellentpreservative and then painted and (B)window sash and frame not treatedbefore painting. Both treatments wereweathered for 5 years. Note the nor-mally weathered paint good conditionof the wood, and glazing on the treatedstructure. M119770, M119771

fungicide inhibits surface decay ormildew.

Be sure to purchase the correcttype of water-repellent preservative.Any type of water-repellent preser-vative can be used as a natural ex-terior finish by itself, but only someare paintable. Manufacturers havealso developed water-repellentpreservatives specifically for exteriorfinishes.

Water repellants are alsoavailable. These are simply water-repellent preservatives with thepreservative left out. Waterrepellants are not good naturalfinishes, but can be used as astabilizing treatment before primingand painting.

Before purchasing and using awater-repellent preservative or waterrepellant, read the label carefully andfollow the manufacturer’s directions.

B

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Varnishes

Varnishes; synthetic resins; andother clear, film-forming finishesprovide an attractive finish for woodsince they allow the natural woodcolor and grain to show through.Unfortunately, the durability ofthese finishes on wood under theaction of sunlight and moisture islimited. Regardless of the number ofcoats applied, the film will begin tocrack and peel, and the finish willhave to be completely removed bysanding or with a varnish removerbefore a new coat is added. Insevere exposures, clear film finishesmay last barely 1 year. Alternatefinishes such as semitransparentstains and water-repellent preser-vatives will give a longer servicelife and are easier to refinish.

Exterior marine or spar varnishesmay be used with some success onexterior doors and other areas ifadequate protection from theweather is provided.

Preservatives

Wood preservatives are not con-sidered to be finishes. However,wood properly treated with a woodpreservative can withstand years ofexposure to severe decay and insectattack without being affected. Thecommon wood preservatives fallinto three general categories. Theseare creosote, pentachlorophenol inoil, and the waterborne salttreatments such as chromated copper arsenate (CCA). Creosote andpentachlorophenol in oil result in adark and oily surface. Odor withcreosote is a problem. Wood thathas been pressure treated withcreosote or pentachlorophenol in

oil is not recommended for usearound the home where people willcome in contact with it. However,wood treated with waterborne saltsis suggested for use in patio decks,outside steps, privacy fences, andother home structures. This materialis generally light to bright green orbrown in color. It can be used out-doors without finishing and will re-main practically unchanged orweather to a light gray.

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Applying Wood Finishes

Paint

Proper surface care and prepara-tion before applying paint to woodis essential for good performance.Wood and wood-based productsshould be protected from theweather and wetting both on thejob site and after they are installed.Surface contamination from dirt, oil,and other foreign substances mustbe eliminated. Weather permitting,it is best to paint wood surfaces assoon as possible after installation.

To achieve maximum paint life,follow these steps:

1. Wood siding and trim shouldbe treated with a paintable water-repellent preservative or waterrepellant. Water repellants protectthe wood against the entrance ofrain and dew and thus prevent

swelling and shrinking. They can beapplied by brushing or dipping. Lapand butt joints and the end of panelproducts such as plywood, hard-board, and particleboard should beespecially well treated since paintnormally fails in these areas first(fig. 14). Allow at least 2 warm,sunny days for adequate dryingbefore painting the treated surface.If the wood has been dip treated,allow at least 1 week of favorableweather.

2. After the water-repellent preser-vative or water repellant has dried,the bare wood must be primed.Since the primer coat forms a basefor all succeeding paint coats, it isvery important. For woods withwater-soluble extractives, such asredwood and cedar, the bestprimers are goodquality oil-base

Figure 14–Paint normally fails firstaround the ends and edges of a board.Liberal application of a water-repellentpreservative can prolong paint life inthese areas. M8330013-5

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and alkyd-base paints. Some latex-base primer paints are also designedfor use over these woods. Theprimer seals in the extractives sothat they will not bleed through thetop coat. A primer should be usedwhether the top coat is an oil-baseor latex-base paint. For species thatare predominately sapwood andfree of extractives, such as pine, ahighquality acrylic latex-base paintmay be used as both a primer andtop coat. Enough primer should beapplied to obscure the wood grain.Do not spread the primer too thin.Follow the spreading rates recom-mended by the manufacturer. Aprimer coat that is uniform and ofthe proper thickness will distributethe swelling stresses that develop inwood and thus prevent prematurepaint failure.

3. Two coats of good qualityacrylic latex-base house paintshould be applied over the primer.If it is not practical to apply two topcoats to the entire house, considertwo top coats for fully exposedareas on the south and west sides.Areas fully exposed to sunshine andrain are the first to deteriorate andtherefore should receive two coats.On those wood surfaces best suitedfor painting, one coat of a goodhouse paint over a properly appliedprimer (a conventional two-coatpaint system) should last 4 to 5years, but two coats can last up to10 years. Thus, three coats of paintslast twice as long as two coats.

4. One gallon of paint will coverabout 400 square feet of surfacearea. However, coverage can varywith different paints, applicationprocedures, and surfaces. Researchhas indicated that the optimumthickness for the total paint coat

(primer and two top coats) is 4 to 6mils or about the thickness of asheet of newspaper. The quality ofpaint is usually, but not always,related to the price. Brush applica-tion is always superior to rollerapplication.

Additional Tips on Painting

To avoid future separation be-tween paint coats, the first top coatshould be applied within 2 weeksafter the primer and the secondcoat within 2 weeks of the first. Ascertain paints weather, they canform a soaplike substance on theirsurface, this may prevent properadhesion of new paint coats. Ifmore than 2 weeks elapse beforeapplying another paint coat, scrubthe old surface with water using abristle brush or sponge. If necessaryto remove all dirt and deterioratedpaint, use a mild detergent. Thenrinse well with water and allow thesurface to dry before painting.

To avoid temperature blistering,oil-base paints should not be ap-plied on a cool surface that will beheated by the sun within a fewhours. Temperature blistering ismost common with thick paintcoats of dark colors applied in coolweather. The blisters usually showup in the last coat of paint and oc-cur within a few hours to 1 or 2days after painting. They do notcontain water.

Oil-base paint may be appliedwhen the temperature is 40°F. orabove. A minimum of 50°F. isdesired for applying latex-basepaints. For proper curing of thepaint film, the temperature shouldnot drop below 50°F. for at least24 hours after paint application.

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Low temperatures will result inpaint failure.

To avoid wrinkling, fading, or lossof gloss of oil-base paints andstreaking of latex-base paints, thepaint should not be applied in theevenings of cool spring and falldays when heavy dews form beforethe surface of the paint hasthoroughly dried.

Solid-Color Stains

Solidcolor stains may be appliedto a smooth surface by brush orroller application, but brush applica-tion is best. These stains act muchlike paint. One coat of solid-colorstain is adequate, but two coats willprovide better protection and longerservice.

Unlike paint, lap marks may formwith a solid-color stain. Latex-basestains are fast drying and are morelikely to show lap marks than theoil-base ones. To prevent lap marks,follow the procedures suggestedunder application of semitransparentpenetrating stains. Solid-coloracrylic latex stains are the mostdurable of these finishes.

Semitransparent Penetrating Stains

Semitransparent penetrating stainsmay be brushed or rolled on.Brushing will give better penetrationand performance. These stains aregenerally thin and runny, so ap-plication can be messy. Lap markswill form if stains are improperlyapplied. Lap marks can beprevented by staining only a smallnumber of boards or a panel at onetime. This method prevents thefront edge of the stained area from

drying out before a logical stoppingplace is reached. Working in theshade is desirable because the dry-ing rate is slower. One gallon willusually cover about 300 to 400square feet of smooth surface andfrom 150 to 200 square feet ofrough surface.

For long life with penetrating oil-base stain on rough-sawn orweathered lumber, use two coatsand apply the second coat beforethe first is dry. Apply the first coatto a panel or area as you would toprevent lap marks. Then work onanother area so that the first coatcan soak into the wood for 20 to60 minutes. Apply the second coatbefore the first coat has dried. (Ifthe first coat dries completely, itwill seal the wood surface so thatthe second coat cannot penetrateinto the wood.) About an hour afterapplying the second coat, use acloth or sponge to wipe off the ex-cess stain that has not penetratedinto the wood. Stain that did notpenetrate will form an unsightly sur-face film and glossy spots. Avoid in-termixing different brands orbatches of stain. Stir stainthoroughly during application.

NOTE: Sponges or cloths that arewet with oil-base stain are par-ticularly susceptible to spontaneouscombustion. To prevent fires, burythem, immerse them in water, orseal them in an airtight containerimmediately after use.

A two-coat wet system on roughwood may last as long as 10 yearsin certain exposures. If only onecoat of penetrating stain is used onnew wood, its expected life is 2 to4 years, but succeeding coats willlast longer.

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Water-Repellent Preservatives

The most effective method of ap-plying a water-repellent preservativeis to dip the entire board into thesolution. However, brush treatmentis also effective. When wood istreated in place, liberal amounts ofthe solution should be applied toall lap and butt joints, edges andends of boards, and panels (fig. 15).It is important to apply liberalamounts of the solution to the endgrain of wood. Areas especially

vulnerable to moisture, such as thebottoms of doors and windowframes, should not be overlooked.One gallon will cover about 250square feet of smooth surface or150 square feet of rough surfacewhen used by itself. The life expec-tancy is only 1 to 2 years, depend-ing upon the wood and exposure.Treatments on rough surfaces aregenerally longer lived than those onsmooth surfaces. Repeated brushtreatment to the point of refusal willenhance durability and performance.

Figure 15–Water-repellent preser-vatives should be applied to all jointsbefore painting. ML835331

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Refinishing

Paint

If you are refinishing an old paintcoat, proper surface preparation isessential if the new coat is to givethe expected performance. First,scrape away all loose paint. Usesandpaper on any remaining paintto “feather” the edges smooth withthe bare wood. Then scrub any re-maining old paint with a brush orsponge and water. Rinse thescrubbed surface with clean water.Wipe the surface with your hand. Ifthe surface is still dirty or chalky,scrub it again using a detergent.Mildew should be removed with adilute household bleach solution.Rinse the cleaned surfacethoroughly with fresh water andallow it to dry before repainting.Areas of exposed wood should betreated with a water-repellentpreservative or water repellant,allowed to dry for at least 2 days,and then primed. Top coats canthen be applied.

It is particularly important toclean areas protected from sun andrain such as porches and side wallsprotected by overhangs. These areastend to collect water solublematerials that interfere with adhe-sion of the new paint. It is probablyadequate to repaint these protectedareas every other time the house ispainted.

Latex-base paint can be appliedover freshly primed surfaces and onsome surfaces where an oil-basepaint has already been used andweathered. Where old surfaces areto be repainted with latex-basepaint, a simple test should be con-ducted first. After cleaning the sur-face, repaint a small, inconspicuousarea with latex-base paint and allowit to dry at least overnight. Then, to

test for adhesion, firmly press oneend of an adhesive bandage ontothe painted surface. Jerk it off witha snapping action, If the tape is freeof paint, it tells you that the latex-base paint is well bonded and thatthe old surface does not need prim-ing or additional cleaning (fig. 8). Ifthe new latex-base paint adheres tothe tape, the old surface is toochalky and needs more cleaning orthe use of an oil-base primer.

Solid-Color Stains

The same technique used torestore a paint coat can be used forsolid-color stains.

Semitransparent Penetrating Stains

Semitransparent penetrating stainsare relatively easy to refinish. Ex-cessive scraping and sanding areusually not required. Simply use astiff bristle bush to remove all sur-face dirt, dust, and loose woodfibers and then apply a new coat ofstain. The second coat ofpenetrating stain often lasts longersince it penetrates into small surfacechecks, which open up as woodweathers.

Water-Repellent Preservatives

Water-repellent preservatives canbe renewed by a simple cleaning ofthe old surface with a bristle brushand an application of a new coat offinish. To determine if a water-repellent preservative has lost its ef-fectiveness, splash a small quantityof water against the wood surface.If the water beads up and runs offthe surface, the treatment is still ef-fective. If the water soaks in, thewood needs to be refinished.

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Warnings

Refinishing is also required whenthe wood surface shows signs ofgraying.

NOTE: Steel wool and wirebrushes should not be used to cleansurfaces to be finished withsemitransparent stains or water-repellent preservatives since smalliron deposits may be left behind.Pentachlorophenol may cause ironremaining on the surface to cor-rode. The corrosion products maythen react with certain wood extrac-tives to form a dark-blue, unsightlydiscoloration, which becomessealed beneath the new finishingsystem. Pentachlorophenol is pre-sent in some semitransparentpenetrating stains and water-repellent preservatives.

Do not mix bleach with ammoniaor with any detergents or cleanerscontaining ammonia! Mixedtogether the two are a lethal com-bination, releasing a gas similar tomustard gas, as well as ammoniaand chlorine gases. In several in-stances people have died frombreathing the fumes from such amixture. Many household cleanerscontain ammonia, so be extremelycareful with what types of cleanersyou mix bleach.

Use caution with wood finishesthat contain pesticides or preser-vatives. When used improperly,they can be injurious to humanbeings, animals, and plants. For safeand effective usage, follow thedirections and heed all precautionson the labels. It is advisable to wearunlined protective gloves and tocover nearby plant life when usingwood preservatives. Do not use anywood finish containing pen-tachlorophenol indoors.

Avoid drift from pesticides ap-plied as a spray. They may con-taminate the surroundingenvironment.

Store finishes containingpesticides in original containersunder lock and key-out of reach ofchildren and pets-and away fromfoodstuffs. Follow recommendedpractices for the disposal of surplusfinishing materials and containers.

NOTE: Registrations of pesticidesare under constant review by theU.S. Environmental ProtectionAgency. Use only pesticides thatbear a Federal registration numberand carry directions for home andgarden use. Since the registration ofpesticides is under constant reviewby State and Federal authorities,you should consult with a respons-

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ible State agency as to the currentstatus of the pesticides discussed inthis report.

U.S. GOVERNMENT PRINTING OFFICE: 1983 - 412-523 - 814/280