Concrete floors, no matter how well-poured, often have high and low spots that make covering the material with tile or hardwood difficult. You could level the floor physically, grinding down high points and filling in low points with mortar, but even then you'll have slight variations in floor height remaining. The best way to create a level surface is by pouring an overlay of self-leveling compound. A painted concrete floor can interfere with the leveler, however, preventing the leveler from binding successfully with the concrete. With a bit more preparation, though, you can cover even a painted floor successfully, giving you the hard, level surface you need for any floor covering you may choose.
Clean the surface of the floor by wet-mopping with a pH-neutral cleanser. Remove all dirt and debris present with the mop, and then rinse the surface of any cleanser residue with clean water. Allow the floor to dry before you continue.
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Remove any peeling paint, using a floor scraper and a broom.
Scarify the floor, using a concrete grinder. Run the grinder over the surface of the floor, applying light force to the pad to scratch the surface of the paint. This scratched surface will aid in adhesion of the bonding agent and leveler.
Apply a coating of latex bonding agent over the floor to help the leveler adhere to the painted concrete. Use paintbrushes to apply the agent to the floor along the walls in about a 3-inch strip, and then spread the agent over the rest of the surface of the floor with a squeegee, working in rows along the floor that overlap by approximately 2 inches to ensure full coverage. Allow the bonding agent to dry overnight.
Fill a large bucket with the amount of water required according to the leveler manufacturer's instructions, less 10 percent. Add the leveler to the bucket of water and mix thoroughly, using an electric drill equipped with a paddle bit. Add the last of the water over a two-minute period, after mixing the leveler completely, in order to smooth out the leveler texture.
Pour the leveler onto the concrete floor and spread the mixture to a depth of approximately ¼ inch, using a squeegee to spread the material. Allow the leveler four hours of drying time. While drying it will level further, removing any high points or voids.