Flooring is important to a remodelling project, as it sets the tone of a room. However, if you have a concrete floor and want other flooring, you will need a sub-floor. You'll need to install a plywood floor over the concrete.
Sweep the floor clean of any debris. Apply the asphalt mastic to the concrete floor with the trowel and allow to set for two hours. Avoid direct contact of the mastic with your skin.
Roll out the asphalt felt and cut to fit. Overlap the edges 3 inches and repeat the process until the flooring is covered by the felt.
Cover the felt with the 6- or 8-mil rolls of plastic, overlapping the edges 3 inches. Roll the plastic out perpendicular to the direction of the felt to avoid any matching lines. Cut to fit. The plastic will ensure no moisture from the concrete flooring is able to reach the plywood or upper flooring.
Measure and cut the first piece of 3/4-inch plywood to fit in the corner in a diagonal pattern. Laying the plywood in a diagonal pattern will ensure the joint lines do not line up with the upper flooring. Allow for a 1/4-inch gap between the plywood and each wall. Allow for a 1/2-inch gap between each sheet of plywood. Attach the plywood to the concrete using the charged nailer. Nail the centre of the plywood to the floor first, then the ends and every 10 to 14 inches around the edges.
Repeat until the concrete floor has now been fully covered with the new plywood sub-floor.