For example, you don't need to buy an expensive piece of plywood that's perfect on both sides if only one side will be seen. Similarly, there's no sense in paying for 1/2-inch thickness when 3/8-inch plywood is really all you need. Plywood also comes with different glues, veneers, and degrees of finish. By knowing these characteristics you may be able to save money as well as do a better job.
Plywood is a commonly used material because it resists shrinking and cracking.
Plywood is broadly categorized into two types: exterior and interior. Exterior plywood is made with nothing but waterproof glue and should always be used for any exposed application. Interior plywood, made with highly resistant glues, can actually withstand quite a bit of moisture. There is interior plywood made with IMG (intermediate glue), which is resistant to bacteria, mold, and moisture, but no interior plywood is made for use outdoors.
When purchasing plywood, look for a back stamp or edge marking bearing the initials APA or DFPA. APA stands for American Plywood Association, while DFPA is the Douglas Fir Plywood Association. These two organizations represent most of the plywood manufacturers, and they inspect and test all plywood to ensure quality is high and grading is accurate. The most critical plywood grading category for most home projects is the appearance grade of the panel faces (see the chart on plywood grades below).
|Interior Grade||Face||Back||Inner Plies||Common Uses|
|A-A||A||A||D||Cabinet doors, built-ins, and furniture where both sides show.|
|A-B||A||B||D||Alternate for A-A. Face is finish grade; back is solid and smooth.|
|A-D||A||D||D||Finish grade face for paneling, built-ins, and backing.|
|B-D||B||D||D||Utility grade. One paintable side. Used for backing, cabinet sides, etc.|
|C-D||C||D||D||Sheathing and structural uses such as temporary enclosures, subfloor. Unsanded.|
|Underlayment||C-plugged||D||C,D||For underlayment or combination subfloor-underlayment under tile and carpeting.|
|Exterior Grade||Face||Back||Inner Plies||Common Uses|
|A-A||A||A||C||Outdoors, where appearance of both sides is important.|
|A-B||A||B||C||Alternate for A-A, where appearance of one side is less important. Face is finish grade. |
|A-C||A||C||C||Soffits, fences, base for coatings.|
|B-C||B||C||C||For utility uses such as farm buildings, some kinds of fences, base for coatings.|
|C-C plugged||C-plugged||C||C||Excellent base for tile, backing for wallcoverings, high-performance coatings.|
|C-C||C||C||C||Unsanded, for backing and rough construction exposed to weather.|
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