Painting Badly Stained Concrete Flooring

Remove any old paint from the concrete flooring with a scraper, wire bristle brush or heavy grit sandpaper. Sweep or vacuum the concrete floor clear of any dirt and debris. Remove any oil or grease stains with tri sodium phosphate (TSP). TSP is a dry cleaning powder that is mixed with water specifically to help with the removal of grease and oils. It can be found in nearly any home improvement center. Mop the floor clean with fresh water and allow the flooring to dry.

Mix together concrete patching compound with water according to the manufacturer's instructions and fill any holes or dips in the concrete floor. Use a trowel to feather the edges out evenly on the floor, if it is necessary. Some concrete patching compounds are self-leveling, which means they don't need to be smoothed out. Let the concrete patching compound set up overnight.

Fill in any cracks with an epoxy concrete crack filler. Follow the specific instructions that come with the epoxy filler. Most epoxy fillers have two compounds that are mixed together, then applied to the cracks and smoothed with a disposable plastic drywall knife. They usually set up within 24 hours.

Sweep and mop the floor again, and allow the concrete to fully dry. Test the concrete floor for moisture penetration by taping 4-foot-by-4-foot squares of plastic to multiple sections of the floor. Tape over each edge of the plastic to ensure any moisture that comes through the floor will be trapped by the plastic. Wait for 24 hours and look for any moisture under the plastic. If there is moisture, a concrete sealer will need to be applied before painting. Apply concrete sealer with a 1/4-inch nap roller and allow it to dry completely. There are also colored concrete sealers that can be used in place of concrete paint.

Apply primer to the floor with a 1/4-inch nap roller. Only use primer that is specifically for concrete. Use a paint brush to “cut in,” covering the edges of the concrete floor by the walls with paint where it would be difficult to paint properly with the roller. Allow the primer to dry overnight.

Apply the first coat of paint with a 1/4-inch nap roller, and “cut in” all the edges as you did with the primer. Allow the first coat to dry and apply at least one more coat of paint until the floor is adequately covered. Again, use paint that is specifically designed for going on concrete floors. For concrete floors that remain badly stained after all the cleaning and priming, several extra coats of paint may be needed, depending on the paint color chosen.