If you are going to do some home remodeling, it is a good idea to do it right the first time. Here are some very important basic steps on how to lay hardwood flooring over your existing cement slab.
Sweep and Prime Slab
Sweep the slab clean and prime the surface. After the primer is dry, snap chalk lines 16′ apart at right angels to the direction the flooring will run. Cover the lines with rivers of adhesive applied to a width of about 2′. The adhesive can be an asphalt mastic designed for bonding wood to concrete or a suitable adhesive of another type designed for the same purpose. (If heating is in the slab, the adhesive should be resistant to heat.)
The bottom sleepers should be 1′ x 2′ strips treated with wood preservative. Embed the strips in the adhesive and also secure them to the slab with 1 1/2′ concrete nails, approximately 24′ apart. the sleepers should be of random lengths and laid end to end with slight spaces between the ends, not butted tightly together.
Lay Polyethylene Film
After all bottom sleepers have been installed, 0.004 polyethylene film should be laid over the strips. Join the polyethylene sheets by lapping edges over sleepers.
1 X 2S to Be Nailed
The second course of 1 x 2s (which do not have to be preservative treated) would be nailed with 4d nails, 16′ to 24′ apart. Nail through the top sleeper and the polyethylene into the bottom sleeper.
Install Flooring at Right Angles
Install the flooring at right angles to the sleepers by blind-nailing to each sleeper, driving at an angle of approximately 50 degrees. Nails should be the threaded or screw type, cut steel, or barbed. Two adjoining flooring courses should not have joints on the same sleeper. Each strip should bear on at least one sleeper. Provide a minimum of 1/2′ clearance between flooring and wall to allow for expansion.