Test the absorbency of the concrete by pouring a small amount of water on the floor to see how quickly it soaks in. If the water forms beads, that means the concrete was sealed and painting will not work.
Remove oil spots on the floor using a de-greaser. Scrub with a stiff-bristle brush and then wipe with clean rags.
Sweep and clean the garage floor to ensure a smooth surface. Remove stains with bleach or a concrete cleaner and a brush. A pressure washer may be necessary to remove tough stains.
Rinse the garage floor with a hose or pressure washer. Use a squeegee or wet/dry vacuum to remove standing water and dirt off the floor. Allow the floor to dry completely.
Repair cracked concrete by using a concrete-repair compound.
Apply primer using a roller on an extension pole. Give the primer at least 8 hours to dry.
Paint the floor using a roller and paint brush. Wait at least 24 hours before applying the second coat of paint.