Just like a wooden sub floor, a concrete slab must be cleaned from dirt, grease, paint, oil or any other debris. Cracks within the concrete slab must be filled with the appropriate
materials. The concrete slab must be flat and smooth with no high and
low spots. High spots must be sanded down so that they are even with
the concrete slab. Low spots must be filled with cement based material
or a self leveling cement with density of at least 3000 PSI. The
variation must be lower than 1/8” over 6’ of concrete.....