Although you can glue hardwood flooring boards to most subfloors, nailing them with a flooring nailer is easier and creates a better floor. The nailer drive cleats at the correct angle to hold the boards down and wedge them together at the same time. When you use glue, however, keeping the boards tightly wedged against one another until the glue dries can be difficult, especially if the boards are warped. Although you can't use a flooring nailer on a concrete subfloor, you can lay plywood first, then nail the flooring to the plywood.
List of Items Needed
- Floor leveling compound
- Handheld oscillating tool with hook and loop pad and coarse-grit sandpaper
- Moisture barrier
- 3/4-inch tongue and groove plywood
- Hammer drill
- 1/4-by-6-inch masonry drill bit
- 16d nails
- Flooring nailer
- 1 1/2-inch flooring cleats
Level the concrete subfloor, if necessary, by spreading floor leveling compound on low areas and sanding down high areas with a handheld oscillating tool with hook and loop pad accessory and coarse-grit sandpaper. Concentrate on large bulges and depressions that will prevent the plywood from laying flat. Vacuum the floor after the leveling compound dries and you are finished sanding.
Spread a clear plastic, vinyl or tarpaper moisture barrier over the subfloor to prevent water vapor from seeping into the plywood and flooring. You can let the barrier float over the subfloor; you do not need to glue or tape it down.
Lay 3/4-inch tongue and groove plywood directly on top of the moisture barrier.
Drill a hole through the plywood and into the subfloor with a hammer drill and a 1/4-inch masonry bit. The hole should be 3 to 4 inches into the concrete, so use a bit that is at least 6 inches long.
Drive two 16d nails into the hole with a hammer. Hold the nails together so the heads are together and tap them into the hole, then keep pounding to sink them completely. Ensure that the nails stay together so you are always hitting both of them at the same time.
Nail down one sheet of plywood, spacing the nails 12 to 24 inches apart, then lay another sheet. Tap it into the first to lock them together and nail it off. Continue until the floor is covered.
Lay the flooring by nailing it to the plywood with a flooring nailer and 1 1/2-inch flooring cleats.
Tips and Warnings
- The plywood layer raises the level of the floor an extra 3/4 inch, so you may have to make or buy special moldings if you need to transition the new floor into an existing one.
- An alternate method for nailing the plywood to the subfloor is to do it with a nail gun that uses an explosive charge to drive the nails. You can also glue it, but If you use glue, place the moisture barrier between the plywood and the flooring instead of between the plywood and the subfloor. Gluing isn't recommended if the floor is below grade and moisture is likely to be present.