Grease spills on concrete can happen as a result of spilled fluids during an automotive repair or spattered grease from grilling. Whatever the source of the oil stain, it's important to remove it as soon as possible. Though concrete is sturdy and long-lasting, it's porous in nature and will absorb the grease. You must draw the grease out of the concrete in addition to cleaning the surface.
Pour cornmeal over the grease stain on the concrete. Use enough to completely cover the stain and leave it there for 20 minutes to absorb excess oil. Repeat if more grease remains, then sweep up with a broom and dustpan.
Combine 1 oz. trisodium phosphate with 1 cup warm water in a bucket. Add 1 cup baking soda. Put on rubber gloves and goggles, then mix the ingredients with a paint stirrer.
Spread the mixture over the remaining grease stain with a scraper. Leave the paste on your concrete surface until it dries. As the mixture dries, it will draw the grease stain out of the concrete.
Scrape up the dried trisodium phosphate paste and throw it away. Wet a nylon scrub brush and pour a few drops of dishwashing detergent onto the scrub brush. Scrub the site of the grease stain on your concrete surface with the soapy brush.
Pour water over the concrete to rinse off the soap suds. Towel dry your concrete surface. Allow it to air dry completely.