Check the concrete basement floor for any sign of dampness. The floor must be completely dry to paint it successfully. Bring in a professional to take care of any leaks if you see damp spots or puddles of water. You also may need to run a dehumidifier.
Sand any rough spots or repaired areas of the floor with sandpaper to make sure the surface is as smooth as possible. Sweep away any residue.
Clean the floor. Scrub an extremely dirty floor with a scrub brush and detergent. Spread cat litter on any oil stains to soak them up, then scrub the floor. Let the floor dry thoroughly before applying primer.
Apply a thin, even coat of primer with a paint roller. Let it dry thoroughly, for one to five hours, depending on the humidity. Run a dehumidifier to speed up the drying process, especially if your basement is damp. Apply a second thin coat of primer and allow it to dry.
Spread a coat of stain blocker on the floor with a paint roller, to help the primer bond more effectively with the latex paint. In some cases you can simply add stain blocker to the primer. Let the stain blocker dry according to the label directions.
Apply a thin, even coat of latex paint with a paint roller. Let the paint dry completely, for an hour or more, depending on the humidity. Apply a second coat of paint and let it dry.