What You Need To Know About Plywood
What You Need To Know About Plywood
Don't be confused about the quality, grading, and types of hardwood plywood. It can really expand the scope of your woodworking projects.
Hardwood plywood can cost about as much as an equal quantity of solid hardwood, depending on grade and appearance. But plywood has many advantages:
Dimensional stability. Crossbanded layers and balanced construction mean that hardwood plywood won't shrink, swell, or warp as much as lumber. Its thin plies, lying at right angles to each other, as well as the various core materials available, produce uniform strength both with and across the grain.
Baltic birch, a widely distributed product from Eastern Europe and Scandinavia, has even better strength.
Varies in thicknesses. Sheets in 1/8", 1/4", 3/8", 1/2", and 3/4" thicknesses eliminate planing and waste.
Large panels. Full 4x8' sheets allow you to work large pieces without edge-joining or otherwise making up width.
Color-matched appearance. In premium grades, at least one side will be uniform in color and grain, making staining and finishing easier.
There Are Some Drawbacks
Hardwood plywood does have its limitations. Keep these factors in mind so you can make the best choice:
Cost. Compared to solid stock on a board-foot basis, hardwood plywood definitely is more expensive.
Limited selection. Because dealers stock what's in demand, your supplier may only have three or four types of hardwood plywood, such as the popular oaks, birch, and mahogany. You may be able to special-order other types of hardwood veneers, but you'll still be limited to a dozen or so of the most common, and no exotic woods. You might approach your project by first determining the type of hardwood plywood available, then selecting the compatible solid stock.
Unreliable stated thickness. The tendency for hardwood plywood panels to vary in thickness from their stated dimension can be frustrating. If you buy a 3/4"-thick panel, for instance, it may stray 1/64" to 1/32" from that thickness. This often is due to the foreign origin of much of this material and the resulting metric thickness measurement, particularly in ash and birch plywood (50 percent or more of which comes from Taiwan, Japan, and Indonesia). Be sure to buy all hardwood plywood for the same project at one time.
Thin face veneers. U.S.-made hardwood plywood has face veneers averaging 1/30" in thickness. Some species, such as black walnut, are sliced thinner, to 1/32". Foreign veneers are thinner still and can be tough to saw without splintering and sand without destroying.
What Are The Veneer Choices?
Veneers, which are nothing more than scant slices off a log, vary in appearance because of the methods by which they're removed. Oak, birch, ash, and other plentiful species lend themselves to peeling by a large lathe. These rotary-cut, continuous slices usually cover a sheet in one piece, producing an erratic grain pattern. Because of this simplified slicing procedure and the elimination of matching and other hand work, rotary-cut veneers cost less.
Flat-sliced veneers come off the log one flitch, or cut, at a time -- just as a potato passes through a vegetable slicer. A surface covered with flat-sliced veneer -- and almost all common hardwoods are available this way -- resembles a series of glued-up boards. This type of veneer is moderately expensive.
Once veneers (other than rotary-cut) have been removed from the log, they must be added to the plywood core. Match refers to their arrangement on the face and back. Slip-matched, the most common way of applying pieces, has consecutive flitches as they come off the log butted up side by side. Book-matched uses consecutive slices, too, but every other one is flipped over for a mirror image. A book-matched face resembles the right and left pages of an open book.
Hardwood plywood grades, set by both the trade association and individual mills, cover varying degrees of quality. But you need to acquaint yourself with only those in the table on the following page.
While not part of the grading standards, the classification of hardwood plywood as either Type I or Type II becomes important to you if your project will be used outside. Most hardwood plywood has Type II adhesive, a somewhat water-resistant bond. For outside applications, you'll want hardwood plywood bonded with truly waterproof Type I adhesive.
A Sampling of Plywood Grades
|Grade||Veneer Quality||Defects allowed|
|A-Premium||If sliced, pieces are slip- or book-matched for pleasing effect of color and grain. Can also be rotary-cut.||Minor, but not frequent burls, pin knots, and inconspicuous small patches.|
|Unmatched slices permitted, but no sharp contrasts in color, grain, or figure.||Burls, slight color streaks, pin knots, and inconspicuous small patches in limited amounts.|
|2-Sound||No figure, color, or grain match.||Smooth patches, sound knots, and discoloration or varying color.|
|G1S||Dealer-applied designation meaning "Good 1 Side" used primarily for foreign-origin plywood of 1/4" thickness; face can be good to premium, back with large defects or of another hardwood species.|
|Shop||Defects downgrade these good or premium panels to factory seconds.|