Installing Plywood Underlayment

When installing new underlayment, make sure it's securely attached to the subfloor in all areas, including under movable appliances. Notch the underlayment to fit the room's contours. Take the time to measure accurately and transfer the correct measurements onto your underlayment.

Rather than notching the underlayment around door casings, undercut moldings and door casings, then insert the underlayment beneath them.

1. Don't overlap seams Installing plywood underlayment is a great way to create a flat reference surface for your new floor. It's fairly quick, and there are only a couple things to be aware of. First, make sure the subfloor is level and there are no dips. Second, to prevent cracks in the new flooring, it's important that the seams of the underlayment don't match up with the seams in the subfloor. Cut the underlayment as necessary to prevent this from happening.
2. Start in corner To install new underlayment, begin by fastening sheets in one corner and work your way across the room. Cut sheets as necessary to prevent overlapping the seams in the subfloor. Fasten the underlayment to the subfloor every 6" or so along the edges and at around 8" to 12" intervals throughout the sheet. Use 1 "-long screws or ring-shank nails. Screws have less of a tendency to "pop" over time and are the best choice.
3. Countersink screws or nails One of the most important steps in installing new underlayment is to make sure that the nails or screws that you're using to fasten it down are countersunk well below the surface. Any fastener that stands proud of, or is even flush with, the surface can tear new flooring or create an uneven surface. Even if it's not noticeable right away, it will likely cause problems in the future. Take the time to check every fastener, and correct any that aren't countersunk properly.
4. Cut to fit Regardless of the room, you'll discover that you need to cut the underlayment to fit around obstacles. Straight cuts are best made with a circular saw. Use a saber saw or coping saw to make circular or curved cuts. Try to cut the underlayment as close as possible to the obstacles to provide maximum support to the new. Instead of cutting around door casings, undercut them.
5. Leveling and sanding To complete the underlayment, mix up some patching compound (or floor leveler) and spread it over seams and screw heads with a wide-blade putty knife or drywall knife. After the compound is dry, scrape off the excess with a sharp putty knife, and sand it flush with the surface with a belt sander and a coarse-grit belt (30- to 60-grit) or with sandpaper and a sanding block. Carefully vacuum up sanding dust before applying the new floor covering.