How to Select Plywood for Carpentry Projects

Plywood is an excellent building material for your carpentry projects. A manufactured material, it has several advantages over lumber: availability in very large sheets, exceptional strength, and high resistance to warp. An odd number of thin wood layers called "veneers" are glued together to form plywood sheets. Each veneer's grain runs perpendicular to the adjacent veneers.

Exterior and interior types are available. Exterior plywood is bonded with glues that won't delaminate even when boiled in water, but it is usually slightly more expensive than interior plywood. Unless the carpentry project will be exposed to excessive moisture or humidity, it's thrifty to choose interior plywood.

All plywood is divided into one of two categories: softwood or hardwood. The difference is in the species of wood covering the outer faces a panel. Although both types are used in cabinetmaking, hardwood plywood is usually considerably more expensive than softwood.

Softwood plywood

The most commonly used plywood is softwood, usually Douglas fir. Other softwood species include Western hemlock, redwood, cedar, Sitka spruce, Southern yellow pine, Western larch pine and white fir. All plywood comes in standard four feet by eight feet sheets. Larger sizes are available and some stores sell quarter or half sheets. Standard thicknesses of softwood plywood are quarter inch, three eighth inch, half inch, five eighth inch and three quarter inch. Some sizes are more difficult to find, for instance five sixteenth, seven eighth and one foot, one eighth inches.

Plywood is graded according to the appearance of the front and back faces. From finest to poorest, softwood grades are designated "N," "A," "B," "C," and "D." "N" is free from defect with uniform color. Use it only where you want a flawless natural finish. "A" grade has neatly-made repairs and is excellent for use where you want a natural finish. "B" surfaces may have oval-shaped repair plugs and tight knots. A good panel from this grade can be finished naturally; poorer panels should be painted. "C" ply can have knots slightly larger than one inch and small splits.

One grade, known as "C-plugged," is more improved and good for painting. "D" grade, the poorest, has larger knots and splits; use this grade where it will be hidden from view. Both faces of a panel are graded - "A-A" would be excellent where seen from both sides; "A-D" is fine where only one side will show. Panels stamped "shop" have been poorly manufactured-if you don't need full panel, perhaps you can salvage enough usable material from a shop-grade panel (beware - some defects are not visible). Buying shop-grade or damaged panels can save you dollars for your carpentry project.

Hardwood plywood

The main types of domestic hardwoods veneered on plywood sheets are ash, birch, black walnut, cherry, gum, maple and oak. Several imported woods, such as lauan, mahogany, teak and rosewood, are also available in some areas. Like softwood plywood, the common sheet size is four feet by eight feet. Thicknesses are one eighth inch, three sixteenth inch, quarter inch, three eighth inches, half inch, five eighth inches, three quarter inch and one inch. Because hardwoods are relatively scarce, lumberyards do not carry all species and thicknesses of hardwood plywood.

In the hardwood plywood category, there are two variations on the plywood theme. One type of hardwood plywood has a core of extra-thick veneer or solid wood. The solid-wood type is called "lumber-core plywood." Another type has a particle-board core. Lumber-core plywood is often used for such projects as table tops or doors that specify butt hinges (the edges can be worked like solid lumber). Particle-board core is very strong with greater dimensional stability. It is also less expensive but quite heavy.

As with softwood ply, both faces of a hardwood plywood panel are graded. Grades of veneers are Specialty Grade ("SP"), made to order; Premium Grade ("#1"), well-matched veneers, uniform color; Good Grade ("#1," too), uniform color and grain; Sound Grade ("#2"), veneers not matched for color or grain and pinhole knots but no open defects; Utility Grade ("#3"), several kinds of defects permitted but fine for painting; and Backing Grade ("#4"), generally used only in concealed areas.

Other veneered materials

Several special-purpose veneered materials are available. Here are the types useful for cabinetmaking:

Grooved (Texture 1-11) plywood

Specially-cut three eighth-inch-wide grooves run the length of these plywood panels, spaced apart from each other at two inches, four inches or eight inches centers. Presently, grooved plywood is available only in one size: five eighth inches. Though an exterior plywood, it can be used for making bookshelves.

Resin-overlaid plywood

This type consists of resin-impregnated sheeting, permanently fused to standard exterior plywood. Because grain raise and checking do not show, it offers an excellent surface on which to paint. Medium-density panels are most commonly used for painting. High-density panels are attractive even when left unfinished.

Wall paneling

Several types of prefinished plywood and hardboard wall paneling are available. Though not very structural, they are an inexpensive solution where large sheets of decorative material are necessary.

Hardwood veneer

Many different species of hardwoods are available for your carpentry project in rolls of very thin veneer. Standard widths of the rolled sheets range from eight inches to twenty-four inches; lengths run from one foot to eight feet. The relatively expensive veneers are usually applied to plywood surfaces using contact cement, a job that requires some practice.

Sources:

Handbook of Finnish plywood, Finnish Forest Industries Federation, 2002, ISBN 952-9506-63-5[1]