The visible portion of your flooring which you see and touch usually has a lower part called an underlayment. And plywood is the most popular choice for floor underlayment.
So why plywood is perfect for Underlayment? Plywood is easily available, low price, and dimensionally stable compared to solid wood. By this I mean that plywood’s perpendicularly-aligned layers make it resistant to sharp changes in humidity and even limited direct contact with water. While plywood is not water-proof by any means but it is considered to be resistant to high moisture.
Is Underlayment a Subfloor? At the base of floors is a subfloor. The subfloor, often plywood itself, rests on the house-joist. The next layer may be the underlayment. Finally, on the top there is the finish floor. Examples of finish flooring are ceramic tile, solid wood, and laminate flooring.
Plywood vs. Other Types of Underlayment, Plywood isn’t the only kind of underlayment for floor. Before you land on plywood as your choice, assess the merits of other types of flooring underlayment:
- Cementboard – Typically used for tile. Tilework requires a lot of water, and this water may compromise plywood’s strength. Cementboard works well for tile. Wonderboard is one brand name of cementboard.
- Fiber Cement Board – A smoother type of cement board. USG’s Fiberock® brand Aqua-Toughâ„¢ is one example.
- OSB – Orient-stranded board – Single-layer composite wood that also can be used as underlayment, though plywood is the best choice. OSB stands up well against moisture.
Type of Plywood Underlayment You Need
Because plywood comes in various grades, you need to buy the right kind of plywood for floor underlayment. AC plywood means that one side is graded as “A” (smooth and sanded), which the other side is graded “C” (rough and exhibiting knots as wide as 1 1/2″). Since the inferior “C” side is facing downward, knots and roughness do not matter.With any type of plywood, you should look for shiplapped or tongue-and-grooved joints. While not absolutely necessary, these joints do make for cleaner seams between the boards.
