MATERIALS : Inexpensive, Sturdy and Flexible Plywood Perfect for Many Projects

Plywood, cheaper and lighter than most solid wood, is strong and flexible, making it ideal for furniture and cabinetry, sheathing and paneling. It is less subject to warping than solid wood and doesn’t shrink or swell with changes in humidity.

Plywood is made of very thin layers of wood (called veneers) that are glued together. On most sheets, the middle layer, or core, is also layers of veneer, but you can also buy sheets that have a solid lumber core. Some specialty sheets have particleboard or fiberboard cores.

Types of Plywood

Veneer-core plywood is stronger than lumber core, but lumber core edges will hold screws more securely than veneer core. You can put screws into veneer core edges, but only if the sheet is at least three-quarters-inch thick, the screw is centered and you drill a pilot hole for it. Usually, to join two pieces of plywood together, you use a glue block, a length of wood screwed and glued on the inside corner between the pieces.

Plywood edges are also vulnerable to chipping and moisture. If the plywood is to be painted, fill the voids in the edges with wood filler and sand them smooth for an attractive appearance. If the plywood will receive a natural finish, cover the edges with iron-on veneer tape. You can also protect the edges with molding, either plain or decorative.

Plywood comes in construction and hardwood varieties. It also comes in interior and exterior grades; waterproof glue is used to bind exterior grade layers together for use outdoors or in water-exposed areas like the bathroom.

Plan your projects with the standard plywood sheet size, 4-by-8-foot sheets, in mind. Before you order a piece of plywood smaller than the standard size, find out if you will be paying for an entire panel. The most common thicknesses for plywood are one-fourth, one-half and three-fourths inches.

Don’t count on the corners of a plywood panel being absolutely square. Industry standards allow a tolerance of 3/32 of an inch between the two corner-to-corner measurements. If true corners are important to a project, plan on cutting a little off the edges of the panel to achieve them.

Grading Standards

Several organizations oversee plywood grading standards. Some, such as the American Plywood Assn. (APA) or the Douglas Fir Plywood Assn. (DFPA) concern themselves only with construction plywood. Others, such as the Hardwood Plywood Manufacturers Assn. (HPMA), deal only with hardwood plywood. Look for their stamps on the back of a panel before you buy it.

For most uses, choose construction grade. Its face and back are softwood, usually Douglas fir, and each sheet is classified by the quality of veneer used. Construction grade is further categorized into “engineering grade” (used where strength is needed, such as in sheathing) and “appearance grade” (where looks are important, such as for cabinetry).

In the construction variety, the top grade is “N” (natural) in which the surface is smooth and evenly matched with no open defects. It is suitable for an unpainted, natural finish. Other grades are “A” to “D” in descending order of quality, depending on the number of imperfections that appear on the face. Sheets are available in various face-and-back grade combinations. “A-B” is suitable when both face and back panels will show. “A-C” or “A-D” is suitable if only the “A” side will show. “C-D” is used in construction projects such as for concrete forms.

Decorative hardwood plywood is classified by the species of wood from which the face is made and by the quality of the veneer.

“Premium” or “A” is best. Next is “good” or “B” or “1”. Either is usable for cabinetmaking, as is “Specialty” or “SP”--a veneer with an unusual quality, such as wormy chestnut or bird’s-eye maple. Other grades are “2” to “4” in descending order.