Construction plywood

U.S. Product Standard, PS 1-83 for Construction Plywood, National Bureau of Standards, U.S. Government Printing Office Washington, DC, 1983. 

Construction plywood panels (1.2 x 2.4 m) are made from rotary peeled softwood veneers of 2-6 mm thicknesses in grades generally admitting large defects. A typical mill would process 100 000 m per year. 

OSB was developed explicitly as an alternative to plywood, at a time when that industry was faced with falling availability of modestly priced, large diameter logs for traditional construction plywood. OSB capacity has increased rapidly and now provides a competitive alternative to plywood sheathing over the timber frame of a North American house. While most OSB production is in North America, capacity is increasing elsewhere, particularly in Europe but also in South America. While initial growth was as a replacement for plywood, it has evolved to fill new market niches. 

Adhesive Distribution. The adhesive is frequently applied as a continuous film in plywood and laminated lumber using roller spreaders and curtain coaters. Spray applications rapidly are becoming the standard for construction plywood. Particle, flake, and fi-berboards are spot welded by small amounts of adhesive, relative to surface area, applied as liquid droplets with spray nozzles or applied as powder particles with a molten slack wax or wax emulsion to temporarily bind the powder particles to the wood surface. 

Construction plywood is primarily phenolic bonded for an exterior rating. Decorative plywood is primarily bonded with UF resins for interior applications such as wall panels and hardwood flooring tiles. Both types of plywood are composed of layers of veneer or wood with alternating grain orientations that are bonded with heat and pressure. 

Adhesive systems for construction plywood, decorative plywood, LVL (laminated veneer lumber), and lumber laminates are a heterogeneous mixture consisting primarily of resin with extenders, fillers, and catalysts. The adhesive mixture allows for a better matching of adhesive with mill operating parameters than would easily be obtained solely with the use of neat resin. 

Construction and Industrial Plywood APA Product Standard PSl-95, APA—The Engineered Wood Association, Tacoma, Wash., 1995. 

The Mosquito was a laminated wood monocoque design that although unusual, was not new. More uniquely, the monocoque shell was fabricated by gluing plywood skins to balsa wood core. This construction foreshadowed the popular honeycomb core/facesheet aluminum and composite designs of later years. Fuselage halves of the Mosquito were formed in closed wooden female tools (tools... 

Wood is one of the oldest constructional materials. Historically it was important in world exploration and trade, and the defence of that trade, in the provision of merchant ships and navies. It was also important in the early days of railway engineering and in building construction. Although in many applications wood has been replaced by other materials, this renewable resource now supports the growing industries of manufactured wood products. Prominent amongst these are the panel materials chipboard, flake-board, strandboard, plywood and blockboard, hardboard and softboard, wood-cement products and the products of the very large pulp and paper industries. 

A laboratory can sometimes save money by building a simple hood where no hazardous, flammable, or corrosive fumes are involved. In one case, a hood was needed solely for drawing off unpleasant fumes from a muffle furnace and water vapor. A carpenter constructed a plywood box which reached from counter top to ceiling and had a large opening in the front. This was painted with a resistant paint, primarily to seal the surfaces and make them easy to clean. An inexpensive fan exhausted the hood to the outside. This simple hood worked for many years. 

Below-grade walls may be constructed of poured concrete, masonry blocks, or other materials such as all-weather wood or stone. This chapter discusses details for use of poured concrete and masonry foundation because these are the materials most commonly used for new construction. Recently, trade associations such as American Plywood Association (APA) and the National Forest Products Association (NFoPA) have issued publications on designing radon resistance permanent wood foundations. Information on these types of foundations can be found by contacting the appropriate trade association.21... 

When we compare the radon concentrations for the dwellings with clay, concrete wall construction and wooden or printed plywood, the values for clay walls are highest, as shown in Figure 5. The medians of the distributions for clay, concrete wall structure and wooden or printed plywood are 27.8, 18.0 and 11.2 Bq/m, respectively. 

Figure 5. Cumulative frequency distributions of radon concentration for dwellings with different wall constructions clay, wooden and plywood, and concrete. Numbers, arithmetic means and S.D.s, geometric means, medians, and ranges of radon measurements are also indicated at the bottom of the figure.

The insulation was 3.5-in.- (90-mm-) thick, unfaced, glass-fiber insulation (friction-fit). Walls with insulation also had a 4-mil clear polyethylene vapor barrier on their interior side. All wood and gypsum materials were conditioned at 23°C and 50 percent relative humidity, resulting in moisture content of 9 to 10 percent in wood materials. Figure 1 is a diagram of the wall frame construction. The hardboard siding was on the exterior side of the 5/8-in. (16-mm) plywood (not shown). 

Our results are comparable to the results of Brenden and Chamberlain (6) and Chamberlain and King (7). In our most comparable assembly having gypsum on the fire-exposed side and no insulation (B-3) (Fig. 7), contribution from the walls started approximately at 30 min and rose to about 200 kW at 50 min. Similar results were obtained despite differences in assembly constructions. The exterior sheathing in our tests was plywood whereas that of Brenden and Chamberlain (6) was gypsum. Moreover, we used untreated wood studs in our assemblies. 

The two major uses of phenol in 1995 were the production of bisphenol-A (35%) and the production of phenolic resins (34%) (CMR 1996). The largest use for bisphenol-A is as an intermediate in the production of epoxy resins (Thurman 1982). Phenol-formaldehyde resins comprise over 95% of this market (Thurman 1982). The plywood adhesive industry required 26% of the total production of phenolic resins in 1977. These low-cost, versatile, thermoset resins have other major uses in the construction, automotive, and appliance industries (Thurman 1982). 

Interior partition walls should be noncombustible construction, such as fabricated of drywall (gypsum board) on metal studs or equivalent. Wood or plywood wall paneling or other combustible construction materials should not be used. The use of wallpaper or other thin wall coverings is acceptable. 

Debate is continuing on the safety and toxicity of formaldehyde and its products, especially urea-formaldehyde foam used as insulation in construction and phenol-formaldehyde as a plywood adhesive. Presently the TLV-STEL of formaldehyde is 0.3 ppm. Formaldehyde is on the Reasonably Anticipated to Be Human Carcinogens list. 

Thermosets A number of thermosets have been used as adhesives. Phenolic resins were used as adhesives by Leo Baekeland in the early 1900s. Phenolic resins are still used to bind together thin sheets of wood to make plywood. Urea resins have been used since 1930 as binders for wood chips in the manufacture of particle board. Unsaturated polyester resins are used for body repair and PUs are used to bond polyester cord to rubber in tires, and vinyl film to particle board, and to function as industrial sealants. Epoxy resins are used in the construction of automobiles and aircraft and as a component of plastic cement. 

Phenol is produced through both natural and anthropogenic processes. It is naturally occurring in some foods, human and animal wastes, and decomposing organic material, and is produced endogenously in the gut from the metabolism of aromatic amino acids. Phenol has been isolated from coal tar, but it is now synthetically manufactured (EPA, 2002). Currently, the largest use of phenol is as an intermediate in the production of phenolic resins, which are used in the plywood, adhesive, construction, automotive, and appliance industries. Phenol is also used in the production of synthetic fibers such as nylon and for epoxy resin precursors such as bisphenol-A. 

Sample Collection. Samples were collected using a 4 foot cubic chamber of 1/4 inch plywood. A special pump and cassette rack was constructed to assure that all cassette and impinger openings were at the same level, Figure 1. 

For the construction, the Sulphlex binders were produced in nominal 7500 lb (3400 kg) batches in rectangular metal vessels with loosely fitted plywood covers. Two batches of each formulation were required. Details of the production of the binders and of the pavement construction have been reported elsewhere (9). 

Wood (qv) is aiguably the oldest building material used by humans to construct their dwellings. It is a natural product obtained from trees, used in both structural and decorative applications. The chemical composition of wood is largely cellulose (qv) and lignin (qv). Today there are a variety of composite or reconstituted wood products, such as plywood, particle board, wood fiber boards, and laminated structural beams, where small pieces of wood or wood fiber are combined with adhesives to make laiger sheets or boards (see Laminates). 

Plywood is also favored for its resistance to splitting and punctures in normal construction applications. Thicknesses range from j (0.63 cm) to s in. (1.9 cm) with the common sheet dimension of 4 x 8 ft (1.2 x 2.4 m). The number of plies commonly range from three to five, but hardwood plywoods may have more. The outermost plies are called faces or face plies. Inner plies with the grain parallel to the face are called core(s) or center, whereas those with the grain direction perpendicular to the face are called the crossbands. 

Softwood plywood is usually used for construction application and is the type commonly found in local lumber and home center stores. The face plies are generally fir. Shipments in 1989 were estimated at 5.02 billion. The Pacific Northwest represented 42% of the total whereas 36% came from the South. 

Plywood is a panel made from wood veneers (thin slices or sheets) bonded to one another. Generally each ply is oriented at right angles to the adjacent ply, and the two face plies should have the grain direction parallel to each other. Thus most plywood will have an uneven number of plies, such as 3, 5, 7, or more. An exception to this is a four-ply construction in which the two core plies are oriented parallel to one another and perpendicular to the two face plies. 

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