What is Plywood?
Plywood is a remarkably strong composite typically made of thin veneers of wood peeled from logs (plies), that are sandwiched together with binders, pressed, and heated. The plies are laid at different angles, so the grain goes one way on one layer, then the next way on the next layer, and so on. While wood tends to contract and expand with moisture across the grain, the alternating layers stifle that movement, making plywood more dimensionally stable than the average 2x4. The composition and materials of plywood make it resistant to warping, twisting, cracking, breaking, and shrinking. Three plies are the minimum, and generally the more plies, the better. The vast choices in plywood stem from the vast uses for it. Did you know that certain types are used for airplanes? And other types for boats? And other types for furniture? And for roof decking and subfloors? These wide-ranging uses mean that numerous types of plywood are on the market—though not necessarily in your local home improvement store, which will typically carry plywood for exterior sheathing, roofing, subfloors, shelving, cabinets, and furniture.
3 Ways to Finish Plywood Edges
Types of Plywood
Different projects call for different types, grades, and sizes of plywood.
Veneer core plywood is the basic plywood with layers of wood bonded together. It’s very strong. MDF core is comprised of layers of wood ply sandwiching a core of MDF, or multi-density fiber. It’s very stable with a more consistent thickness than veneer core plywood and is often used for doors. Lumber core plywood is comprised of lumber sandwiched between veneer layers. It’s often used for long shelves. ApplePly is a brand name for a high-end type of veneer core plywood with many hardwood plies that is used for drawers and furniture where the edges are visible and sometimes become design elements in and of themselves. The face can be made of various types of hardwood, though it’s often maple. Exterior sheathing plywood is often used for lateral bracing on building exteriors and is rated CDX. The “C” is the rating on the face, the “D” is the rating on the back, and “X” is for Exposure, which means it’s meant for outside use when covered with siding, for example. It has exterior rated glue. Subfloor plywood is waterproof, and usually of greater thickness (¾ inch to 1 1/8 inch). It should be tongue and groove (indicated by T&G on the sheet) for a squeak-free floor.
Plywood Grades
The grade refers to the physical appearance of the plywood.
Grade A: The face and back of the sheet is nearly free of defects, with a smooth, sanded surface and virtually no knots. Good for cabinet doors and furniture, the surface is meant to be seen (not covered with another material) and can be painted or stained. Other terms for Grade B: Sanded smooth, but the face and back have a few defects, some of which have been repaired with patches or wood filler. Less costly than Grade A. Grade C: Unsanded, with tight knots up to 1 ½ inches wide. There may be large areas that have been patched and filled. Good for subflooring or other applications where it will not be seen. Grade D: Unsanded, with knot holes up to 2 ½ inches wide and liberal use of patches and filler and some unrepaired defects. Like Grade C, good for structural uses where it will not be seen.
When two grades are indicated, such as A/B, the A refers to the face and the B refers to the back.
Plywood Sizes
Plywood panels are generally available in three main sizes:
4 ft. x 8 ft. 4 ft. x 9 ft. 4 ft. by 4 ft.
The plywood thickness you choose depends on the needs of the project. Different types of plywood are available in a dizzying array of sizes. Generally speaking, plywood is made from 1/8-inch-thick, to more than 1 ½ inches thick. Most plywood in a big box store will be ½ inch, ¾ inch, and 1 inch. Very thin plywood is appropriate for as an underlayment between subflooring and tile. However, thicker plywood is needed for the actual subfloor, or for structural sheathing fastened to the framing members on a new shed. Building codes should be followed.
Buying Plywood
When you head out to the home improvement store or lumberyard to buy plywood, it’s best to know what you need in advance. For plywood that will be stained or painted, choose grade A or B, according to your budget, and look closely at the side that will be exposed. There can be substantial variation between one sheet and the next, so don’t hesitate to pull out and examine several sheets before purchasing. If the edges will be exposed, make sure there are no holes or gaps in them.
