APA Engineered Wodd Handbooks Episode 11 pps

9.1 CHAPTER NINE TREATMENTS AND FINISHES FOR WOOD Richard Carlson Senior Scientist, TSD 9.1 INTRODUCTION Wood exposed to weathering must be protected from the elements in order to maintain its appearance and integrity. Exposure to sunlight and moisture can dam- age wood surfaces. Additionally, unprotected wood exposed to extended periods of high moisture is subject to decay and attack by wood-destroying organisms, which can undermine its integrity and structural adequacy. Finishes such as paints and stains help protect wood surfaces from ultraviolet light and rapid fluctuations in moisture content. Although many finishes contain additives to provide some degree of protection from surface molds and fungi such as mildew, these additives provide little protection from wood-destroying fungi or insects. Various types of chemical treatments are available, however, which can provide protection from these organisms. The type and extent of treatment needed will vary depending on the severity of exposure and associated risk factors. Addi- tionally, not all treated wood products are paintable. Therefore, if a product is to be finished, it is important to specify the use of a paintable wood preservative. Finally, awareness is increasing of environmental and health concerns associated with the use of some chemicals for treating wood. The U.S. Environmental Protec- tion Agency (EPA) requires the registration of all preservatives used in products manufactured for treating wood. They also publish guidelines for the handling and disposal of some types of treated wood. Further guidance on this subject is available from the American Wood-Preservers’ Association. 9.2 PRESERVATIVE TREATMENTS Wood may be preservatively treated through various processes such as brush- applied or dip applications, addition of preservatives into the product during man- ufacture, or pressure treatment after manufacture. To select the most suitable method, one must consider various factors such as code requirements (if applicable), 9.2 CHAPTER NINE the severity of exposure, level of protection required, cost, availability, and per- formance expectations. 9.2.1 Dips or Surface Applications Nonpressure treatments such as water-repellent preservatives or other preservatives are available that can be applied by brush or dip treatment. The latter method is generally more effective when practical. These types of treatments provide limited protection in lower decay risk applications or in nonstructural situations. They are topical and provide little penetration on wood surfaces, although they are readily absorbed by the end grain. If brushed on, they should be liberally applied and worked into any open voids. Dip treatments are most effective when the product is immersed for several minutes. Follow the manufacturer’s recommendations. Surface treatments are not as effective as pressure-preservative treatments in protecting wood. Not all water repellents contain preservatives and many are not paintable. Therefore, it is important to specify a product suitable for the intended end use. Other types of treatments, such as copper naphthenate and copper-8-quinolinolate, are also available for surface applications. Copper-8-quinolinolate may be used in accordance with FDA and/or USDA regulations where food contact with the treated wood is possible. 9.2.2 Blended Treatments There are currently no existing treating standards for OSB, LVL, or I-joists. How- ever, some manufacturers have evaluated the use of preservatives incorporated into the furnish of OSB. Furnish may be defined as wood-based material, such as flakes or strands, including applied resin, wax, and other additives, as the primary con- stituent of wood-based panels such as waferboard or oriented strand board (OSB). These blended preservatives are intended to provide protection from wood-destroy- ing organisms. Check with the manufacturers for additional information. Other products, such as LVL, may be treatable with pressure processes or brush-on ap- plications or dip treatments, subject to agreement between buyer and seller. The suitability of any of these processes will depend on many factors, such as devel- oping technology, the effect of the treating process and/or treatment chemicals on the durability of the glue bond, the effectiveness and penetration of the preservative, and the level of decay hazard. 9.2.3 Pressure-Treated Plywood Most construction applications don’t require preservative-treated wood. But in some uses, and in certain climates, treated wood is recommended or required by local building codes to protect against decay, fungi, termites, carpenter ants, or other wood-destroying insects, or from marine borers in seawater exposure. Preservative- treated plywood is impregnated with preservatives by a pressure process. The re- sulting deep penetration of preservative provides protection against decay and insect attack. See below, Standards and Use Recommendations, for a summary list of AWPA standards for plywood. Pressure-preservative-treated plywood is used in a variety of applications: TREATMENTS AND FINISHES FOR WOOD 9.3 • Wood foundations • Bulkheads • Retaining walls • Swimming pools • Highway noise barriers • Irrigation structures • Cooling towers • Electrical transformer vaults • Decks, docks, piers, and floats • Tanks • Liquid manure storage tanks • Planters • Food transport, processing, and storage • Roof, wall, and floor sheathing in tropical regions or applications where resistance to termites or decay is required Preservative-treated plywood maintains stiffness and strength, thermal properties, workability, light weight, and economy. Wood preservatives and wood treated with these chemicals should be used and handled appropriately (see below, Standards and Use Recommendations and Pre- cautions for Use and Handling). Always follow the recommendations provided by the preservative manufacturer or wood-treating company. Acceptances and Availability. Preservative treatments are recognized in model building codes, federal and military specifications, and American Association of State Highway and Transportation Officials (AASHTO) specifications. Preservative-treated plywood is generally available in most metropolitan areas. For availability, contact local building materials suppliers or consult the Yellow Pages of the telephone directory under ‘‘Lumber Treating.’’ Some panel grades, thicknesses, span ratings, or species may be difficult to obtain in some areas. Check with your supplier for availability or include an alter- native panel in the specifications. Organic Preservatives. Organic preservatives used for preservative treating of ply- wood include creosote, pentachlorophenol (penta), and copper-8-quinolinolate. Creosote is a coal tar product that is dissolved in a distilled solution or petroleum oil. It is an effective preservative in commercial, industrial, or marine applications when there is severe exposure to decay or insect attack, or marine borers in saltwater environments. Creosote-treated plywood has an odor and a dark, oiled surface ap- pearance and therefore is not recommended where painting is required. Penta is commonly dissolved in light petroleum oil or solvent or in a petroleum solvent/water solution. It is suitable as a preservative for ground contact or above- ground uses. Plywood treated with penta has an odor, and oil-borne penta has an oiled surface appearance and thus is not recommended for painting. However, ply- wood treated with solventborne or waterborne penta, including penta in LPG, has an oil-free surface and natural wood appearance and should be specified where staining or painting is desired. Note: Penta dissolved in methylene chloride should 9.4 CHAPTER NINE TABLE 9.1 Chemical Names of Common Waterborne Preservatives ACA Ammoniacal copper arsenate a ACZA Ammoniacal copper zinc arsenate a CCA Chromated copper arsenate a (types A, B, and C) ACC Acid copper chromate ACQ-B Ammoniacal copper quat (type B) a ACQ-D Amine copper quat (type D) CC Ammoniacal copper citrate SBX Borate oxide a These preservatives are highly leach-resistant. not be used to treat plywood containing synthetic repairs in face veneers, since the solvent can damage the repairs. Plywood treated with copper-8-quinolinolate preservative can be used in appli- cations where food is harvested, transported, or stored. The preservative is dissolved in liquid petroleum gas or light hydrocarbon solvents so that the treated plywood has a clean surface and is free of solvent odor. Check with the company providing the treatment service regarding applicable FDA and USDA acceptances. Inorganic Preservatives. Inorganic preservatives are the most popular and com- monly available types used for preservative treating of plywood. They include leach-resistant waterborne arsenical preservatives such as CCA, ACA, ACZA, and ACQ-B, which are highly effective in preventing decay and attack by termites, carpenter ants, and marine organisms (see Table 9.1 for chemical names of common waterborne preservatives). These preservatives are forced into plywood under pres- sure and become insoluble or fixed in the wood cells after impregnation and drying. Waterborne preservatives are recommended where clean, odorless, and paintable products are required. Wood treated with such preservatives may be used inside residences or commercial and industrial buildings, providing sawdust and construc- tion debris are cleaned up and disposed of after construction. Note: Treatment of tongue-and-groove (T&G) panels with waterborne preser- vatives may result in difficulty in mating T&G edges. Using square-edge panels or milling T&G edges after treatment should be considered. Standards and Use Recommendations. Table 9.2 lists applicable American Wood-Preservers’ Association (AWPA) preservative-treating standards for plywood, according to the intended end use. Table 9.3 summarizes plywood applications and recommended preservative treatments for these uses, in accordance with AWPA Standards. Preservative Penetration and Retention. AWPA standards specify preservative retention in terms of pounds of retained preservative per cubic foot of wood. Spec- ified retention levels vary according to the type of preservative and the severity of exposure (see Table 9.3). For preservative-treated plywood, AWPA standards require that all veneers must be penetrated by preservative. The net retention of preservative in plywood is high—up to 25 lb/ft 3 in some treatments—because of plywood’s high ratio of surface area to volume. Therefore, preservative-treated plywood may be cut in the field without loss of preservative protection at cut edges. TREATMENTS AND FINISHES FOR WOOD 9.5 TABLE 9.2 Preservative-Treating Standards for Plywood a Use Preservative types AWPA standard Creosote Pentachlorophenol Copper-8- quinolinolate Waterborne preservatives General C9 X X X X Highway C14 X X Commercial- residential construction C15 X X Farm C16 X X X X Marine C18 X X X Wood foundation C22 X Food handling, storage, transportation C29 X Cooling tower C30 X X a For government and military procurement, Federal Specification TT-W-571 should be cited when spec- ifying preservative-treated wood. Fasteners. Hot-dipped or hot-tumbled galvanized steel, stainless steel, silicon bronze, or copper fasteners are recommended for use in preservative-treated wood. Only stainless steel fasteners are recommended for attaching preservative-treated plywood to lumber below grade in wood foundations. Gluability. Plywood can be glued when treated with most of the waterborne pre- servatives and with some penta treatments using light petroleum oil or solvent, liquid petroleum gas, or petroleum solvent/water as a carrier. Consult treating firms or their trade associations for specific recommendations. Structural Properties. Preservative treatments applied under AWPA standards do not affect plywood strength and stiffness. See APA Plywood Design Specification 1 (Form Y510) or APA Technical Note N375 2 for allowable working stresses and section properties or design capacities for plywood. Finishing Recommendations. Waterborne preservatives are readily paintable when dried after treatment. Finishing recommendations are generally the same as those for untreated plywood. Some slight surface degradation is possible in sanded plywood after drying because of surface checking and/or discoloration. For this reason, Medium Density Overlay plywood gives best results where treated paintable surfaces are required. Unsanded grades of plywood do not require further finishing but can be finished with two-coat acrylic paints or opaque stains. Stain finishes or two-coat acrylic paints (stain-blocking primer and topcoat) are recommended for textured plywood. Painting plywood treated with creosote or oil-borne preservatives such as pen- tachlorophenol is not recommended. Painting can be done only with difficulty and 9.6 TABLE 9.3 Recommended Treatments Exposure Typical application a Minimum preservative treatment b (lb/ft 3 by assay) Creosote Pentachloro- phenol d Copper-8- quinolinolate f Waterborne preservatives c Contact with sea water, exposed to marine borer attack. Pontoons, wharf bulkheads, scows, floats and flood gates, etc. Creosote: full-cell 2.50 Not recommended Not recommended ACZA 2.50 ACA 2.50 CCA 2.50 (Type A, B or C) Contact with ground, chemicals, continuous moisture, or high humidity. Permanent trench and tunnel lining, retaining walls, skirting for post and pier or pole-type foundations, snow sheds, floats, irrigation structures, tanks, linings for wet process industries, poultry dropping trays, septic tanks, some chemical storage tanks, industrial sewers, and smelter roofs. Creosote: empty-cell 10.0 Penta: empty-cell 0.50 Not recommended ACZA 0.40 ACA 0.40 ACC 0.40 CCA 0.40 (Type A, B or C) ACQ 0.40 (Type B or D) CC 0.40 Permanent wood foundation system e Not recommended Not recommended Not recommended ACA, 0.60 ACZA, CCA (Type A, B or C) or ACQ (Type B) 9.7 Above-ground uses where plywood is subject to insect infestation or fungus attack. Under these exposure conditions, protection may be advisable for subflooring over unexcavated areas or shallow crawl spaces; sheathing and other uses such as fences, exterior siding, exposed structural units such as stressed-skin panels and box beams, reservoir roofs, splash boards in pole-type buildings. Creosote: empty-cell 8.0 Penta: empty-cell 0.40 Copper-8- quinolinolate: empty-cell 0.20 ACZA 0.25 ACA 0.25 ACC 0.25 CCA 0.25 (Type A, B or C) ACQ 0.25 (Type B or D) CC 0.25 SBX g 0.17 Interior linings of refrigerators and box cars; food processing plants and warehouses; greenhouses and milk processing facilities; fruit, vegetable, and grain harvesting; transport and storage containers requiring low human toxicity fungicide. Not recommended Not recommended Copper-8- quinolinolate: empty-cell 0.20 Not recommended a See applicable EPA-approved Consumer Information Sheet (CIS) for precautions involving uses and handling of creosote, pentachlorophenol or inorganic arsenical pressure-treated wood. b Recommended minimums from the American Wood-Preservers’ Association Standards. c Based on dry preservative per cubic foot, oxide basis, full-cell treatment. d Oil, gas or other solvent-borne. e Plywood marked PS 1 or PS 2, or APA Standard PRP-108 is required for the Permanent Wood Foundation system. f Volatile petroleum (AWPA P9, Type B) or light hydrocarbon (AWPA P9, Type C) solvents only. g For dry above-ground applications not subjected to liquid water or Formosan termites. TABLE 9.3 Recommended Treatments Exposure Typical application a Minimum preservative treatment b (lb/ft 3 by assay) Creosote Pentachloro- phenol d Copper-8- quinolinolate f Waterborne preservatives c 9.8 CHAPTER NINE TABLE 9.4 Use Precautions for Pressure-Treated Wood a Application Organic preservatives Creosote Pentachlorophenol Inorganic preservatives Arsenicals 1. Skin contact applications. OK b OK b OK 2. Residential interiors. No No c OK 3. For industrial and farm buildings, interior components which are in ground contact and subject to decay or insect attack. Also see application 5. OK b OK b OK 4. Laminated beams for commercial or industrial buildings No OK b OK 5. Interiors of farm buildings when animals can crib (bite) or lick the treated wood. No No OK 6. Agricultural farrowing or brooding facilities. No No OK 7. Applications where preservative may become component of food or animal feed, such as structures or containers for storing silage or food. No No No 8. Cutting boards or countertops for preparing food. No No No 9. Decks, patios and walkways if surface is visibly clean and free from residues. OK OK OK 10. Portions of beehives which may come into contact with honey. No No No 11. Applications where treated wood can come into direct or indirect contact with drinking water for public or animal consumption. No d No d No d a Based on EPA-approved Consumer Information Sheets. b Must be painted with recommended sealer (two coats). c Except for glued laminated beams or for building components which are in ground contact and are subject to decay or insect infestation and where two coats of an appropriate sealer are applied. d OK for incidental contact such as bridges or docks. requires extensive care using an aluminum base paint. Paintable pentachlorophenol treatments are available. (See discussion under Organic Preservatives.) For certain interior applications in commercial, industrial, or farm buildings, creosote- or pentachlorophenol-treated wood may be used if exposed surfaces are sealed by painting with two coats of urethane or epoxy paint or shellac (varnish may also be used for pentachlorophenol-treated wood). For guidelines on use pre- cautions in these cases, refer to Table 9.4 and the EPA-approved Consumer Infor- mation Sheet (CIS) for the applicable preservative treatment. Precautions for Use and Handling. The chemical formulations used for preser- vative treatment of plywood are registered with the EPA, which has approved guide- lines for the use of pressure-treated wood to ensure safe handling and avoid envi- TREATMENTS AND FINISHES FOR WOOD 9.9 ronmental or health hazards. The use precautions for creosote, pentachlorophenol, and inorganic arsenical preservative-treated wood are published in EPA-approved Consumer Information Sheets (CISs) for these treatments, available from treaters, and are briefly summarized in Table 9.4. Handling Tips • Treated wood should not be burned in open fires or in stoves, fireplaces, or residential boilers. • Treated wood from commercial or industrial use (e.g., construction sites) may be burned only in commercial or industrial incinerators or boilers in accordance with state and federal regulations. • Avoid frequent or prolonged inhalation of sawdust from treated wood. When sawing and machining treated wood, wear a dust mask. Whenever possible, these operations should be performed outdoors to avoid indoor accumulations of air- borne sawdust from treated wood. • When power sawing and machining, wear goggles to protect eyes from flying particles. • Avoid frequent or prolonged skin contact with pentachlorophenol- or creosote- treated wood; when handling wood treated with these chemicals, wear long- sleeved shirts and long pants and use gloves. • After working with treated wood, and before eating, drinking, or using tobacco products, wash exposed skin areas thoroughly. • If preservatives or sawdust accumulates on clothes, launder before reuse. Wash work clothes separately from other household clothing. 9.2.4 Preservative Treatment of Glued Laminated Timber Structural glued laminated timbers (glulams) bearing the APA EWS trademark are produced by members of Engineered Wood Systems (EWS), a related corporation of APA—The Engineered Wood Association. These glulams are manufactured to conform with AITC/ANSI Standard A190.1, American National Standard for Structural Glued Laminated Timber. 3 Although glulams do not require preservative treatment for most uses, certain applications may present environmental conditions conducive to decay or insect or marine borer attack. Conditions that favor such attack are the presence of moisture (20% or greater moisture content of the wood) accompanied by temperatures rang- ing from 50–90 ЊF. Decay progresses more slowly at temperatures outside this range and virtually ceases at temperatures below 35 or above 100 ЊF. These hazards are typically controlled through recognized design principles and construction techniques such as use of overhangs, flashings, ventilation, and proper joint connection details such as shown in Chapter 12. Elimination of potential decay hazards through effective design detailing is the preferred method of controlling decay. When hazards of decay or insect attack cannot be avoided, glulams must be pressure-preservative treated or a naturally durable species must be used. Examples of construction where such hazards may exist include direct exposure to weather, ground contact (including direct contact with concrete foundations and footings), contact with fresh water or seawater, and exposure to excessive condensation. Outdoor uses of preservative-treated glulams include bridges, utility structures, marine applications, highway noise barriers, and decks. Indoor uses that may re- 9.10 CHAPTER NINE quire pressure treatment include environments subject to high humidity or conden- sation, such as indoor swimming pools or greenhouses, where moisture content of the wood may exceed 20%. Indoor applications such as post and beam construction in some farm buildings may also involve ground contact and thus require preser- vative treatment for those members in contact with the ground. Table 9.5 lists common preservatives used to pressure-treat glulams and provides a summary of relevant considerations. Applicable Standards. Applicable standards for preservative treatment of glulams include American Wood-Preservers’ Association Standards C28 4 (and all other stan- dards referenced therein) and M4. 5 Related specifications include American Forest and Paper Association National Design Specification; 6 American National Standards Institute, Inc. ANSI A190.1; Federal Specification TT-W-571, 7 and American As- sociation of State Highway and Transportation Officials (AASHTO) (Standard Specification for Preservative Pressure Treatment Process for Timber). 8 Preservatives. Pressure preservative treatments listed in American Wood Preserv- ers’ Association (AWPA) Standard C28 for glulams include creosote, pentachloro- phenol, copper naphthenate, and water-borne inorganic arsenicals. Other treatments and processes specified should be agreed to by purchaser, seller, and governing code body. Required retention and penetration levels depend on end use and exposure according to AWPA or other applicable specifications. Organic Preservatives. Organic preservatives listed in AWPA Standard C28 include creosote and pentachlorophenol and are the primary treatments used in glulams manufactured from western species. See Section 9.2.3 under Organic Pre- servatives for a discussion of these organic preservatives. Inorganic Preservatives. Inorganic preservatives are waterborne treatments such as ammoniacal copper arsenate (ACA) and chromated copper arsenate (CCA). While these are not recommended for use with western species, they may be used to treat southern pine laminations prior to gluing of the finished product. See Sec- tion 9.2.3 under Inorganic Preservatives for a further discussion of these inorganic preservatives. Treatment Recommendations. Glulams are available in custom and stock sizes. Stock sizes are typically cut to length at a distribution center or on the job site. Most glulams to be pressure-treated will be custom sizes and should be ordered to exact dimensions, when possible, to avoid field cuts, which must be retreated. In addition, all fabrication, cutting, and predrilling of holes for fasteners is recom- mended prior to pressure treating. Glulams may be treated after gluing, or the individual laminations may be treated prior to gluing, depending on the wood species and treatment specified. Treatments such as creosote or pentachlorophenol (penta) in oil are typically only specified for treatment of the finished member. Penta in light hydrocarbon solvents may be spec- ified for the laminations prior to gluing or for the finished member. Waterborne salt treatments may be specified for laminations prior to gluing. However, glulam man- ufactured using pretreated laminations is not available from all glulam manufac- turers and for use with all species and availability should be verified prior to spec- ifying. The use of waterborne preservatives for the treatment of finished glulam mem- bers is not recommended. The only waterborne preservative listed in American Wood-Preservers’ Association Standard C28 for use after gluing is ACZA, and it is limited to coastal region Douglas-fir, western hemlock, and hem-fir. It is impor- [...]... significantly extend the life of the finish 9.4.2 APA Rated Siding Products APA Rated Siding is a family of wood-based products that includes a wide variety of sidings such as plywood, overlaid oriented strand board, and composite materials Most APA plywood siding products are classified as APA 303 Siding Although the surface characteristics of APA Rated Sidings may vary, APA 303 Sidings can be manufactured in... recommendations provided here are specifically for exterior fin- 9.24 CHAPTER NINE FIGURE 9.2 APA Texture 1 -11 APA 303 Siding panel with shiplapped edges and parallel grooves 1⁄4 in deep, 3⁄8 in wide; grooves 4 or 8 in o.c are standard Other spacings sometimes available are 2, 6, and 12 in o.c., check local availability T1 -11 is available in 19⁄32 and 5⁄8 in thicknesses Also available with scratch-sanded, unsanded,... 12 in., and in lengths to 16 ft Because it is manufactured in long lengths, APA lap siding is simple and easy to install APA lap siding possesses the clean, horizontal lines of traditional lap siding, yet offers excellent dimensional stability and split resistance to help it maintain a consistent, even appearance Finishing APA Rated Siding Whether finishing a new structure or refinishing an older one,... texture running across panel Available without grooves, or with grooves of various styles, and in lap sidings, as well as in panel form Generally available in 11 32, 3⁄8, 15⁄32, 1⁄2, 19⁄32, and 5⁄8 in thicknesses Rough sawn also available in APA Texture 1 -11 , reverse board-andbatten, channel groove, and V-groove Available in Douglas-fir, cedar, southern pine, and other species smooth or texture-embossed overlay... Oil-based, semitransparent stains may be used on certain veneer-faced sidings Solid-color stains may be used on most APA Rated Sidings and generally provide better protection In general, however, APA siding products perform best with all-acrylic latex paint systems Sanded plywood is not an APA Rated Siding material and is therefore not recommended for siding applications However, it is frequently used... continuous patterns Generally available in surface patterns and textures similar to Texture 1 -11 and in 11 32, 3⁄8, 15⁄32, and 1⁄2 in thicknesses Available in Douglas-fir, cedar, southern pine, and other species Solid-color stains, which are available in either latex- or oil-based formulations, may be used on all APA 303 Sidings except brushed plywood Latex-based solidcolor stains should be used on grades... from some mills While HDO is best suited for some applications and MDO for others, either panel may be used for a broad range of jobs Table 9 .11 lists some common uses for which either HDO or MDO offers high performance and low maintenance TABLE 9 .11 Common Uses of APA Overlaid Panels Painted signs Concrete forming Siding Soffits and fascias Cabinets and built-ins Industrial tanks and vats Counter tops... pattern Grooves are typically 4 in o.c Also available with grooves in multiples of 2 in o.c Generally available in 11 32, 3⁄8, 15⁄32, 1⁄2, 19⁄32, and 5⁄8 in thicknesses Depth of kerf grooves varies with panel thickness Film-forming clear finishes, such as varnish, are not recommended on APA Rated Sidings for exterior use, since they tend to fail quickly by flaking and extensive surface preparation is... without much preparation Bleaching finishes (stains or oils) are not recommended for APA Rated Sidings For a natural weathered appearance, use a gray oil-based semitransparent stain Stains should be applied in accordance with the manufacturer’s directions As shown in Table 9.10, semitransparent stains are recommended for plywood APA 303 Siding with face grades of 303-0C (clear, no patches), 303-NR (natural... recommendations TREATMENTS AND FINISHES FOR WOOD FIGURE 9.5 APA Lap Siding Rough-sawn, smooth, overlaid, or embossed surfaces, with square or beveled edges Available in 3⁄8, 7⁄16, and 19⁄32 in thicknesses FIGURE 9.6 Brushed Brushed or relief-grain textures accent the natural grain pattern to create striking surfaces Generally available in 11 32, 3⁄8, 15⁄32, 1⁄2, 19⁄32, and 5⁄8 in thicknesses Available . glued laminated timbers (glulams) bearing the APA EWS trademark are produced by members of Engineered Wood Systems (EWS), a related corporation of APA The Engineered Wood Association. These glulams. strength and stiffness. See APA Plywood Design Specification 1 (Form Y510) or APA Technical Note N375 2 for allowable working stresses and section properties or design capacities for plywood. Finishing. shipment of treated wood. They can also be obtained from the American Wood Preservers Institute or APA The Engineered Wood Association. Use precautions are summarized in Table 9.4 and appropriate sealers