How to Install Flooring Underlayment

Underlayment is the layer of material above the first layer of subflooring and under your floor covering. If you're planning to put down a wood floor, vinyl, carpeting or any other material that moves, plywood makes good underlayment. If you're putting down ceramic or stone tiles, you should use cementboard, Cementboard is harder to work with but provides a stronger, motion-free base and is more water-resistant. Either way, it's important to both glue and screw down the underlayment to prevent squeaks in your floor.

Difficulty:

Moderate

Instructions

Things You'll Need

• Enough 4x8 sheets of either 1/2-inch plywood or 5/8th-inch cementboard to cover the floor, depending on what floor covering you'll use. Carpenter's glue and glue gun Tape measure Pencil T-square Screw gun Box of 1-1/2-inch drywall screws Circular saw Razor knife

1. Thoroughly clean the subfloor. Locate the positions of the floor joists, which should be easily identified by the lines of nails. Lay your level along the center of each area where there's a joist underneath, and mark it all along the subfloor with your pencil, until you have parallel lines across the room showing where the joists are.

2. Lay the first piece of underlayment on its face and spread carpenter's glue around the back of it in a zig-zag pattern, with one line of glue all the way around the perimeter of the piece, a couple inches in from the edge.

3. Turn the piece over and lay it in the far corner of the room, glue side down. Press it into place, then use your screw gun to screw it to the floor, sinking drywall screws every six inches. As you do so, make sure that some of them are hitting the joists, judging where to screw those by the parallel pencil lines that you marked on the floor.

4. Lay the remaining pieces of underlayment down in the same fashion, building off the first and staggering the rows so there are no four-way intersections between the pieces. Cut end pieces as necessary. For plywood underlayment, set your t-square on the wood at the size you need for the space, run a straight pencil line along the square, then set the plywood on sawhorses and cut with your circular saw. For cementboard, stand the board on its long side, set the t-square in place, use your razor knife to cut one smooth deep line, then bend it there until it snaps and cut the back side of the line to separate it.

References

• More information is available here.