Even the best cars sometimes leak a little oil. Once an oil stain has set, it's unlikely that you'll be able to remove it completely. But you can remove most of the discoloration without too much trouble. First, brush or sweep the area to prevent working the grease further into the concrete. You might want to hose the area to help you determine where the stains are the worst. Be sure to let the concrete dry before you resume cleaning it. The simplest way to remove oil stains is to sprinkle dry wood ash over them. Leave the ash in place for 24 hours or more, then sweep it clean. The ash will soak up much of the oil. If your stain is too tough for wood ash, try paint thinner (figure A), also known as mineral spirits. Always wear safety glasses and rubber gloves when working with paint thinner. Pour a little onto the stain, and sprinkle some cat litter or cornmeal over it before it dries up (figure B). Allow the paint thinner to dry for about an hour, then sweep it up. For paint stains, use a citrus-based cleaner. A wide assortment of utensils is available for cleaning concrete (figure C). Nylon scouring pads work well on smooth-finish concrete but tear up easily on concrete with a textured finish. If you need to buy a brush, choose one with a long handle so you won't have to get down on your hands and knees to clean. If you need to mop concrete, don't use a sponge mop. A string mop is more rugged and can work deeper into the crevices on concrete with a brushed finish. If concrete is extremely dirty, you might need to use sulfamic or phosphoric acid (figure D). These cleaners can be dangerous to handle: make sure to read the warning labels so you'll know what to do if you get them on your skin or in your eyes. Take appropriate safety precautions such as wearing acid-resistant gloves and safety glasses. Make sure the ventilation is adequate, or wear an appropriate respirator. If the stains are too deep to scrub away, you may be able to get them out with a grinder. Don't use a sander: the sandpaper will wear out too quickly to do much good. After the concrete is clean, seal it with concrete sealer (figure E) to prevent future stains. Sealer is easy to apply: pour it into a bowl or bucket, and apply it to the concrete with a paintbrush or roller. If you can't find concrete sealer, use paste wax, which also works well. You may not be able to remove all the stains from your concrete. To give the surface a fresher look, stain it before applying sealer. To give concrete the look or brick, stone or other decorative pavement, use templates for applying the stain.
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