Cleaning Concrete Oil Spots
DEAR TIM: Yesterday a dump truck not only left a load of top soil at my home but it also left behind a nasty oil stain in the center of my concrete driveway. I also have some old oil stains on my concrete garage floor. How can I remove these stains and restore the concrete to its original state? Once I get the concrete clean and dry is there a way one can prevent oil stains from seeping into concrete? Gus Z., Elmhurst, IL
DEAR GUS: Motor and hydraulic oils can really cause a mess on concrete, brick and blacktop but the good news is that you can achieve excellent clean up results if you act quickly. Concrete is a dense surface but water and many other liquids can and do soak into the surface. The fresh oil stain created by the dump truck will be a breeze to remove. The older oil stains in your garage may be a far greater challenge.
Removing the fresh stain from the driveway will require a regular scrub brush, some liquid dish soap and water. All you need to do is squirt some liquid dish soap onto the stain and add some water. Be sure to wet down the surrounding concrete as well. This will prevent oil released during the cleaning process from causing a secondary stain. Scrub the stain vigorously and add enough water to make a rich lather of soap.
The soap will emulsify the oil and lift it out of the concrete. If you simply rinse the driveway the oil will pollute your yard or street. You may decide it is more environmentally responsible to blot up a majority of the dirty soap mixture with paper towels or a dry compound like cat litter and dispose of this in a certified landfill. There is a good chance your local waste collection service can accomplish this task for you.
Do not use a wire brush to scrub the concrete. It can erode and scratch the concrete finish resulting in a permanent scar. I have successfully removed many fresh oil stains from my own concrete driveway using a standard nylon bristle scrub brush that I purchased at a local grocery store. Some stains require several scrubbing attempts to completely remove all of the oil.
You can use the same method to attack the older stains in your garage floor. If the concrete finish on the garage floor is quite smooth, you may have a great chance of success. Smooth steel troweled concrete is highly resistant to oil stains. This type of finish, though, is unsuitable for exterior concrete. It simply is too slippery when it gets wet. Rough concrete finishes absorb oil rapidly.
If the old stains do not respond to the soap and water method you can consider using a solvent like kerosene to help lift the stain. But I do not like to use solvents as they are very dangerous to work with. The fumes from these products can ignite and cause serious harm to you and your home. If you decide to work with solvents, I would only do so after consulting with your local fire department's fire prevention officer.
Some people have had success lifting oil stains using muriatic acid. But keep in mind that this chemical, even when mixed one part acid to ten parts water, can and will dissolve some of the cement paste at the surface. Couple this with scrubbing and you very well may alter the appearance of the concrete once it dries.
Clean concrete can be treated to help minimize the penetration of oil and water that contains dirt and pigments. Some of the best products are clear water and oil repellents that contain silane and siloxane ingredients. These chemical solids help block the tiny pores in concrete to stop water from entering and soaking into the concrete. The silane and siloxane products allow the concrete to breathe. This is very important for concrete that is subjected to freezing temperatures. The clear repellents are easy to apply and dry clear.