A Guide to Softwood Plywood

	Manufacturing
	Veneer Grades
	Panel Grades
	Panel Grademarks
	Care & Handling
	Workability
	Fastening
	Gluing
	Finishing

How do you make softwood plywood? You start by cutting thin sheets of wood veneer from logs on a rotary lathe. The veneer is then dried and, finally, bonded together with structural adhesives. Sheets and/or layers of veneer are typically oriented with their grain at 90 degrees to each other and arranged in an odd number of plies or layers, resulting in a structural panel that has its greatest strength axis in the direction parallel to the face grain (typically the 8' direction). Cross orienting of the veneers also produces a panel with excellent dimensional stability by restraining movement across the grain.

Based on the size, type, and frequency of natural characteristics or defects allowed within a sheet, the following section describes the most typical veneer grades used for panels.

Depending on panel grade, higher grades are typically placed on panel faces and lower grades in the inner plies.

Softwood plywood is manufactured to one of two industry standards. PS 2-92 is the performance standard for softwood plywood intended primarily for construction applications. Acceptable performance criteria for various construction applications, such as roof and wall sheathing, flooring, and siding is defined, and panels are evaluated and third party certified. Examples of performance rated panels, certified by APA, the Engineered Wood Association, are "Rated Sheathing" for walls and roofs, "Sturd-I-Floor" for floors and "Rated Siding" for exterior exposure applications.

PS 1-95 is the prescriptive standard for sanded and underlayment grades of plywood. These grades typically have the best face sanded smooth and are typically used where they will be stained or painted, or where a level, smooth panel is required such as underlayment under thin, resilient floor coverings. Typical grades include "A-C", "B-C", and "Underlayment." Softwood plywood manufactured to both standards is further classified by its adhesive bond durability and strength of veneer species utilized in the construction.

Exterior exposure classified panels are bonded with a fully waterproof adhesive and utilize no veneer lower than grade C. They are designed for full and permanent exterior exposure when properly finished. "Exposure 1" classified panels are also bonded with a fully waterproof adhesive but allow grade D veneer in the construction. Exposure 1 durability panels are designed for temporary exposure, but ultimately will be protected and covered by roofing, siding, or another weather- resistant membrane.

The most common species used in the face veneers of domestic softwood plywood are Southern pine and Douglas fir. These species are among the strongest (group 1) and will produce a panel with greater stiffness than lower species groups (groups 2, 3, or 4) when used as face veneers. Lower species groups are typically used in the inner plies, although many Southern pine plywood producers utilize this species throughout the panel construction.

When it comes to plywood, grademarks tell the story.

The APA panel grademarks are examples of both performance rated and sanded grades of softwood plywood found in the marketplace and define the information found on the panel grademark stamp.

Like all wood-based building materials, softwood plywood should be properly stored and handled to assure the desired level of appearance and performance. Panels should be stored under cover (preferably indoors), in dry conditions to prevent excessive dimensional change. Store off the ground or concrete floors on equal height bolsters. For 4' x 8' panels, use a minimum of three bolsters—16" in from each panel end and one in the center. If covered outdoors, do not wrap tight with a tarp; allow for ventilation. Panels should be dry prior to any finishing operation since excess moisture can affect the finish adhesion, appearance and performance.

Softwood plywood can be cut, drilled, router jointed, glued, fastened and finished with ordinary woodworking tools and basic skills. When hand sawing or cutting on a table saw, support the panels firmly with the best face up. Cut with the best side down when using a portable power saw. Do not force-feed the panel into the tool or the tool into the panel too quickly because this will increase the roughness of the cut and may induce splintering-out on the exit side. Proper backup of the material also can reduce splintering.

Nails, staples and screws designed for use with wood products and of the appropriate size can be used separately or in conjunction with an adhesive. If the in-service conditions may be subject to high humidity or wetting, use of galvanized, aluminum or stainless steel fasteners is recommended.

There are many options available. Any adhesive system designed for gluing of wood should be suitable. Consult with your Lowe's Associate to select an adhesive that matches the bond durability to the exposure conditions.

For dry-use interior applications, sanded plywood is often the panel of choice where appearance is of primary importance and the product will receive a decorative finish. Sanded plywood for interior use can be stained with a semitransparent or opaque stain, painted, or finished with a clear topcoat.

Typical grades of sanded plywood have repairs made to the face in the form of wood patches and/or synthetic putty repairs. Putty repairs do not accept stains as readily as the surrounding wood and will result in a different color. For this reason, panels with synthetic repairs are only recommended for opaque stain or paint finishing.

However, Southern pine plywood typically has fewer and smaller repairs than Douglas fir. So, many cuttings from a panel may not contain any synthetic repairs. Even wood patches may not accept the stain exactly the same as the surrounding wood due to differences in density (sapwood vs. heartwood). If in doubt as to the final finished appearance, test finish a scrap piece containing a patch.

For exterior exposures, the recommended finish is an opaque stain or a compatible primer and topcoat paint system. In both cases, a 100 percent acrylic resin latex paint formulation is recommended for best performance. The finish should be brushed with the grain with a minimum of two coats of opaque stain or one coat primer and one coat paint (two coats preferred for best long-term performance). And don't forget to apply finish all the way to the panel edges, especially lower drip edges, and the panel back, too, if exposed.