Q: How do I level a concrete floor with low spots to prepare for tile installation?
A: To install tile, laminate or hardwoods over a subfloor containing some dips, depressions, holes or cracks, you need to level it before you proceed. The best way to do this is with leveling compound. Some of these products can be mixed like mortar and troweled flat over the dips. Other products are marketed as self-leveling compounds, which are a thin, watery type of cement that levels itself out (like liquid) when it is applied to a concrete surface. It dries quickly, so you might want to practice working with it on a hidden surface before you start.
Before applying leveling compound, roll sealing primer over the concrete with a floor roller, working it into the low spots and crevices. Allow the primer cure for 48 hours. Mix the compound with water and apply it to the floor following the manufacturer’s instructions. Work in sections of a few square feet at a time, and use a concrete trowel to spread the edges of the compound and feather the edges flat. Allow the compound to cure for several hours before installing the flooring.