Choosing just the right type of plywood for your construction project can be a confusing task. Many types and grades exist, each suited best for a specific use.
What is Plywood?
Plywood is constructed of layers of wood veneers (known as plies) bonded together at heat and pressure by special adhesives. The grain of the wood in each layer is laid at a right angle to the adjacent layer - resulting in an engineered wood construction material highly resistant to warping, cracking, and shrinking.
What are the different finish grades of plywood, and what do the letters mean?
Plywood at Power Building Products is classed by the finish grades of the surface veneers on each side.
- "A" grade veneer is of the highest quality, and has been sanded smooth and is ready for painting.
- "B" grade veneer is a step down from "A", usually containing a few voids in the veneer. The voids have been filled with a synthetic filler material (or wooden plugs) and the veneer has been sanded smooth.
- "C" grade veneer is considered the lowest "surface grade" material. It isn't usually sanded and it contains slight discolorations and a few voids in the veneer surface.
- "D" grade veneer is unsanded and unfilled, and is usually used where unexposed to elements and hidden from view.
Because plywood contains two sides of veneer, both sides are called out in the specifications. "AC" plywood has one "A" side and one "C" side. "CD" plywood has one "C" side and one "D" side.
The smoothest surface is called the "face," while the rougher surface is called the "back."
What are the different thicknesses and sheet sizes of plywood?
Plywood is usually ordered by calling the nominal thickness as 1/4", 1/2", 3/4", etc - but the sheet will be stamped with the actual thickness.
Depending on the thickness of the sheet and the finish grades, the factory width tolerance will vary. Thin (or hardwood) plywood with an "A" side is usually measured to the nearest 64th of an inch, while thicker unsanded (or softwood) grades will be measured to the nearest 32nd or 16th of an inch.
4'x8' sheets are the most common; however 4'x9', 4'x10', and 5'x10' sheets are also available.
Which types of plywood are used for common applications?
CDX plywood ("C" side, "D" side, eXposure grade) is most commonly used for decking or sheathing applications. An inexpensive "rough" grade, CDX is good choice for surfaces that won't be exposed to water after your project is complete.
AC plywood ("A" side, "C" side) is used when the quality of the finish surface is most important - such as for shelves, furniture, and the like.
Plywood is available in interior grade, exposure grade 1, exposure grade 2, or in exterior grade. The plywood sheet will be stamped with its exposure rating. Your salesman can help you decide which grade is appropriate for your project.
What's the difference between exterior and interior grades of plywood?
Generally speaking, the difference is in the type of adhesive laminating the sheets together. If the sheet must resist water, the glue is very water resistant. When water resistance isn't a consideration, less-expensive laminates are a wise choice.
When it has to be of the highest moisture rating, choose a marine grade plywood.
What is OSB?
OSB is an Oriented Strand Board composite material. Like traditional plywood, its an engineered wood sheet composed of oriented strands of lumber. Unlike plywood (which is composed of 5 or 7 laminated sheets) OSB typically contains about 50 cross-layered strands.
Also known in some areas as waferboard or norboard, OSB is made of chips of wood instead of veneers. For this reason, OSB is usually available at about half the cost of a comparable sheet of plywood and offers shear strength about twice as high as traditional plywood (2 knot holes can never overlap.)
OSB is typically used for roofing and other decking applications.
Professional contractors often choose 3/4" tongue and groove OSB for subfloors.
What is Luaun?
Luaun (also known as Luan) is a thin plywood used primarily in cabinetry. Suitable for closet linings, cabinet backings, door facings, and craft work, luaun is often used as an underlayment for flooring to level an uneven surface. This applications voids the warranty of many flooring products (because luaun lacks the necessary strength and moisture resistance) and for this reason isn't recommended for flooring.
Luaun is available at Power Building Products in 1/4" sheets.