There are multiple chemical methods for removing oil or grease (both hydrocarbon-based materials) from concrete. Small spills or spots can sometimes be removed with nothing more then a strong detergent, a scrub brush, and a sponge. A more aggressive method is to use a commercial concrete cleaner or degreaser, a concentrated alkaline soap that's scrubbed into the concrete surface. The soap acts like ball bearings, loosening up the oil to permit easier removal. The downside is that typical degreasers don't actually break down the oil, so they won't work well on concrete that is heavily contaminated or has been contaminated for a long time. Also, they are more effective on porous concrete as opposed to concrete with a hard or dense finish.
Another common treatment for removing oil stains from concrete is a poultice. Used primarily on small, stubborn stains, a poultice is made by saturating an absorptive material (such as kitty litter, pool filter media, or sawdust) with a strong solvent (acetone, xylene, lacquer thinner, or MEK) and then smearing the material over the stain. Cover the poultice with plastic, and let the process of osmosis take over. The solvent will break down the oil, and the absorptive material will suck it out of the concrete. However, this process takes time and may not be cost-effective or practical for removing large stains. See how a poultice can be used to remove oil from a concrete countertop.
The most recent advancement in the removal of oil stains from concrete involves using special single-celled microorganisms that thrive on crude oil and its derivatives, eating them up like candy. Enzymes and oxygen digest the oil and turn it into carbon dioxide and more microorganisms. When the food source (oil) is gone, the microorganisms die, leaving the concrete clean and oil-free. This is the same technology used to clean beaches and waterways after large oil spills. Two sources for these microbial cleaners are ESI (www.esiclean.com) and KT Microbial Products (www.ktmicrobialproducts.com).
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