Q. I want to do some remodeling projects around my house. I went to a home center store to buy plywood, but there must have been 20 types. How do I know what type to use for various projects?
Plywood is used in many home improvement and woodworking projects. In order to meet the variety of needs, plywood products with various properties are offered, as you have found.
Plywood is categorized in general grades and then further defined by specific properties, wood species and adhesives. The prices can vary significantly, and some premium grades will cost more than solid woods.
Before discussing the various grades and uses of plywood, it helps to understand how plywood is produced. Plywood is made by laminating thin layers of wood together using adhesives to create a strong, thick sheet.
The layers are oriented such that the grain on each sheet is perpendicular to the one above and below it. This gives it strength, size and stability, and minimizes the possibility of warping as moisture levels change. It has an odd number of layers (from three to seven) so that the exposed layer on each side has the grain running in the same direction.
Most plywood has a face side and a back side. The face side is higher quality wood with fewer imperfections, so check both sides of the sheet when purchasing this type of plywood. For projects where both sides will be seen, plywood with two face sides is available.
Basic plywood grades are from A to D, with A being the best and most expensive.
A sheet of Grade A plywood should have few or no blemishes and should be finely sanded. Grade D is the least expensive plywood, and it usually has the maximum number and severity of blemishes allowed.
Depending upon your project, you may not need a high-quality finish on both sides. For those projects, select plywood which is graded A-C. This sheet of plywood will have Grade A quality on the face side, but only Grade C quality on the back side. For strictly structural use, C-D (commonly called CDX) plywood is adequate.
The type of adhesives used varies among plywood products. Indoor plywood, which will not be exposed to high levels of moisture, uses one type of adhesive. This type of plywood can be made of select hardwoods and softwood and can be used for cabinets, furniture, indoor sheathing, etc.
Exterior plywood is the most common type available at most home-center stores. The adhesives are more resistant to high levels of moisture. It is available in the highest grades. Structural plywood uses the strongest adhesives and is most moisture resistant. CDX is the most common grade used.
There are also specialty plywoods for high-quality cabinetry and furniture. These use finely finished hardwood veneers of various species and hardwood core sheets, often made of poplar for stability. These hold a screw well and can be used similarly to solid hardwood sheets. For a curved surface, bending plywood is available. The grains in the layers all run in the same direction for easy bending.