Measure the size the plywood pieces must be to fit in place on the subfloor. Cut the plywood pieces to size using the circular saw.
Leave the cut plywood pieces in the room you will be installing them in for at least three days so the panels can adjust to atmospheric conditions.
Clean the existing subfloor with the vacuum so it is free from dust and debris.
Cut the tip of the subfloor adhesive tube at a 45-degree angle using the utility blade. Load the subfloor adhesive into the caulking gun.
Apply subfloor adhesive to the bottom of the plywood, easily identified by the rough finish. Spread subfloor adhesive in a cross format and all around the edges. The subfloor adhesive will prevent the subfloor from squeaking.
Place the plywood onto the existing subfloor and secure it. The smooth surface of the plywood has to be facing up. Begin hammering the 1 1/4-inch screw/shank nails at an edge, and move toward the opposite edge. Hammer a nail every 6 inches to ensure the plywood is secure to the existing subfloor. Ensure the nails are hammered flush with the plywood or slightly below the surface of the plywood.
Install the remaining subfloor using the same technique. Apply subfloor adhesive beneath the plywood and hammer a nail every 6 inches into the plywood. Let the newly installed subfloor dry for at least 24 hours before installing the finished flooring over it.