Remove all items from the concrete floor and sweep it thoroughly to remove all surface debris.
Apply a degreasing cleaner to any visible stains and allow it to sit for two to three minutes. Scrub the areas with a stiff-bristled brush to remove the stains. Fill a bucket with 1 gallon of water and 2 to 3 tbsp. of liquid dish soap. Scrub the remainder of the floor with the soap solution.
Rinse away the soap residue by refilling the bucket with clean water and mopping the floor with it. If the concrete floor is in a garage, simply spray it down with a garden hose.
Wait until no moisture remains in the concrete floor, which can take two to three days. Locate any paint that is chipping or peeling and sand it down with an 80-grit sandpaper attached to a hand sander. Re-vacuum these areas to remove the sanding dust.
Put on a face shield and chemical-resistant gloves. Open a jug of muriatic acid and create a mixture of one part acid to eight parts water in a bucket. Mop the concrete floor with the acid to etch the surface, which allows for better adhesion of the paint.
Dump out the muriatic acid and rinse the bucket thoroughly with water. Refill it with a mixture of one part ammonia to eight parts water. Mop the floor with a clean mop to neutralize the acid. Allow the floor to dry completely.
Locate any cracks or small chips in the floor and fill them with an epoxy crack filler designed for concrete. Drag a putty knife over the surface after application to smooth it out and remove excess epoxy. Allow the floor to dry for another 24 hours.
Open a can of combination primer and paint designed for concrete. Paint around the edges of the concrete floor using a paintbrush. Pour the remainder of the paint into a paint tray and paint the floor with a 1/4-inch nap roller.
Wait until the first coat of paint is dry and then apply a second coat.