Vacuum the concrete floor to remove dust. If the concrete floor is in the garage or the exterior, use a garden hose or power washer to remove dust and debris from the surface.
Mop the floor with warm water and dishwashing soap to remove additional grime, dust and debris. Then allow the floor to dry.
Scrub stubborn debris from the concrete floor with a scrub brush, water and mild soap. Use a stronger detergent and a cup of ammonia if the debris resists your first attempt. Then allow the floor to dry.
Pour the concrete sealer into a paint pan.
Dip a long-handled, roller brush into the pan. Then apply the sealer to the clean and dry concrete surface. Work in small 3 feet square sections until the surface is completely sealed.