Installing New Underlayment

This story covers installing new plywood underlayment.


No matter how you finish your floor, it will only be as good as its underlayment -- the supporting layer fastened to the joists. Underlayment provides a smooth, stable surface for the finished floor.

You can lay ceramic tile over hardwood and ceramic floors -- if the surface and subfloor are stable and in good condition. The same is true for uncushioned resilient tile or sheet materials on a wood frame floor. But new ceramic tile over an existing floor will raise the surface by at least 3/4 inch. Removing the existing floor will minimize any change in floor levels and reveal any hidden faults that need repair.

If your underlayment shows signs of rot or is not thick enough to support the finished floor, or if you're working in new construction, you'll have to install new underlayment, typically 3/4-inch exterior plywood. Bring the plywood into the room a few days before installation to acclimate it, which will reduce shrinkage or expansion.

Prestart Checklist

From 30 -- 45 minutes per square yard

Tape measure, chalkline, circular saw, cordless drill, screwdriver bit

Measuring and marking, cutting with circular saw, driving fasteners with cordless drill

Remove existing flooring as necessary

3/4-inch exterior grade plywood, construction adhesive (optional), galvanized screws

Step 1

Set up 2x4s as a work surface -- in an area where they won't be in the way. Start with a full sheet in a corner, squaring it with the room and centering its edges on the joists. When cutting pieces measure from the edge of the board to the center of the joist and snap a chalkline for the cut.

Step 2

With old underlayment locate the joists and mark their positions on the wall. Lay the new sheet down and snap perpendicular joist lines to guide the placement of fasteners. Apply a bead of construction adhesive (optional) and drive in screws that are long enough to penetrate the joists.

Step 3

Set half sheets next to full sheets so the joints are offset. Leave at least a 1/8-inch gap between the sheets (an 8d nail makes a good spacer) and 1/4-inch at the walls.

Comments (2)
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6/9/2016 01:34:52 PM Report Abuse
marfilwyoming wrote:

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10/23/2009 09:37:51 AM Report Abuse
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