How to Lay Underlayment

A floor is generally composed of a thick plywood subfloor that sits directly over the joist (support beams), with underlayment on top of the subfloor and the finished flooring on top of the underlayment. Plywood is the preferred underlayment for most types of flooring, including carpet, wood floors, vinyl and even hard tiles, as long as it's a "dry'" room.

Things You'll Need

• 1/4-inch plywood sheets
• Tape measure
• Screw gun
• 1 1/4-inch galvanized wood screws
• Table saw
• Leveling compound
• Drywall knife

Instructions

1. Clean and dry the subfloor. Set your first piece of plywood in one corner of the floor. Use a screw gun to put a 1 1/2-inch galvanized wood screw every 6 or 8 inches across the board's surface, sinking the heads completely.

2. Lay your second board along the wall at the end of the first board, leaving about 1/4-inch of space between the two boards to allow the wood to expand with climate changes. Make sure the seam between the boards doesn't line up with the seam between the subfloor boards. Secure the second board in the same fashion as the first.

3. Lay additional boards in the same manner, end-to-end, leaving the 1/4-inch space between them, until you've spanned the whole length of the floor. Cut the last piece to fit as necessary on a table saw.

4. Start the second course of boards from the opposite wall, using a full board so the end of the board doesn't line up with the end of the boards from the first course. If the first course happens to be all full boards, cut the first board of your second course in half so the ends don't line up.

5. Cover the whole floor in staggered rows, keeping your 1/4-inch space between the boards.

6. Spread leveling compound, using a drywall knife, over the 1/4-inch spaces between the boards, getting it flat and smooth. Also spread compound over the screw holes. Let the compound set for a day.

Tips & Warnings

• For bathrooms and other rooms with a lot of moisture, substitute cement board for the plywood and use thin-set mortar instead of leveling compound.

• Wear eye protection when cutting plywood.

References

• Georgia Pacific: Installation and Preparation of Plywood Underlayment for Resilient Floor Covering