Concrete floors and surfaces can stain easily because of the porous nature of the concrete. Depending on the substance that causes the stain, it can often do more than just mar the look of your concrete, but also shorten the concrete's useful life. Fortunately, a concrete stain can be easy to remove in a few simple steps.
Wash the concrete with a mixture of 1 cup trisodium phosphate (TSP) per gallon of water. Soak the stained area with the TSP wash for 30 minutes and then scrub the area with a plastic bristled brush. Rinse with a hose.
Cover the stain with fresh kitty litter for three days and sweep it away. Alternatively, cover the stain with dry concrete mix and clean it up with a wet mop.
Apply enzymatic solution to the stain to dissolve away the staining substance. Rinse thoroughly with water.
Remove rust stains using oxalic acid. Dilute the oxalic acid following the manufacturer's directions, and mop the floor with the solution. After six or more hours, scrub away at the stain with a plastic bristled brush. Rinse off with clear water. Wear safety goggles and rubber gloves when working with oxalic acid.
Scrub fresh oil and grease stains using mild liquid dishwashing soap and a plastic bristled brush. Work the soap to a thick lather. Use an old towel to blot away the excess soap.
Clean a mold or mildew stain using oxygenated bleach. Also called sodium percarbonate, oxygenated bleach is commonly available as a deck-brightening agent. Mix 1 part oxygenated bleach with 2 parts water and pour the solution into a power washer. Use the power washer to spray the area, and this will almost immediately get rid of the mold and mildew. Repeat often to prevent further mold and mildew growth.