How to Remove Oil Stains from Concrete

Removing persistent stains from grease, oil, and pollutants that can change the appearance of a concrete slab can pose obstacles. Pollution will stain concrete. Airborne dirt can collect on a concrete surface, forming a dark, oily buildup or stain. Grease can leave a nasty, slippery stain.

The number one cause of concrete stains is vehicles. A concrete slab’s main purpose is to park or drive on. A substantial number of vehicles experience some kind of oil leak. Used oil from a vehicle is filled with impurities. These impurities are what leave a concrete stain.

While heat cycles cause oil to darken, soot causes oil to turn black. Most people associate black soot with diesel engines, but gasoline engines can produce soot as well. Soot is a byproduct of incomplete combustion. Soot particles are less than one micron in size. For comparison, human hair is roughly 70 microns in diameter. Being so small, they will not be filtered from the oil with a standard oil filter.

These ultra-fine particles are what cause most concrete stains. Having an understanding of what causes them will help you to reduce their appearance.

Understanding Oil Stains on Concrete

Most stains can be removed from a concrete surface without difficulty. There will be times when it will be necessary to repeat the treatment until the desired results are reached. Experimentation might be needed if the staining material is unknown. After the stain has been removed, a slight shadow still might remain. Concrete is like a sponge and will absorb stain-producing liquids deep into the substrate.

Stains can be removed from concrete by either mechanical means, chemical methods, or a combination of both. Evaluating the chosen process before tackling the entire project will be extremely helpful. However, if the method removes the stain, it could have an adverse reaction producing an undesirable appearance. Again, always evaluate in a small, out-of-the-way spot.

Essential Tools & Equipment for Oil Stain Removal

Common mechanical means consist of sandblasting, flame scarification, shotblasting, and grinding. Brushes can also be used to scrub the surface. The bristle composition will dictate aggressiveness. Metal will be the most aggressive. Copper, aluminum, and steel are metal alloys that are used to produce a wire brush. If damage to the surface is a concern, plastic bristles should be used.

Mechanical means will remove a surface stain. The stained substrate will be removed, exposing the concrete matrix within the concrete. The issue of using a mechanical process is that the surface texture of the slab will be altered. Changing the texture will alter its appearance and look like another stain. If this method is chosen, it might a good to address the entire surface with the same mechanical method. By grinding, shot blasting, or sandblasting the entire area, the surface stain will be removed, and the texture will be similar over the entire area.

Chemical cleaning can be highly effective in stain removal. Chemicals can be applied to concrete without etching the surface. Even weak acids may roughen the surface if left on for any length of time.

Oil can readily penetrate an unprotected concrete surface. If free surface oil is promptly removed, there will be less chance of staining. Poultice material such as Prosoco’ s Oil & Grease Stain Remover can be used to trap surface oil and draw it from the near-surface. Poultice absorbents are applied directly to the stain and left to work overnight. During this time, oil will be wicked into the material. Once removed, the stain might still be noticeable, and a second application can be done.  

Once the surface oil has been removed, the remaining stain can be tackled. With a plastic bristle brush, scrub trisodium phosphate (TSP) into the stain. Saturate well and then apply poultice over the top. This will keep the area wet with TSP for 24 hours enhancing the cleaning process.

If a stain stays, using a commercial stain remover would be a great move. They are generously sprayed on the stained area and vigorously scrubbed with a plastic bristle brush. Once completed, wet the area with clean water and extract with a wet vacuum.

Oil ingesting bacteria microbes can also be used. They are safe, non-toxic, waterless cleaners for the removal of oil, grease, and diesel. The bacteria will ingest the hydrocarbons and leave the surface clean and stain-free. Once applied, the microbes start eating the hydrocarbon, reducing the stain. Allowing the product to cover the stain overnight for best results. Since oily stains penetrate deep into porous concrete, more applications may be necessary.

Preventing Future Oil Stains

Penetrating concrete sealers will not stop oil from staining concrete. Penetrating sealers penetrate below the surface, where they chemically react in the pores. The surface of the concrete is then left exposed. When oil gets spilled onto the surface, a penetrating sealer will slow down the movement of the oil into the pores, but the exposed concrete will stain. Penetrating oil repellants provide an extended window so it can be removed leaving minimal damage. If you spill oil on the surface of concrete, it should be cleaned up at once minimizing staining.

The three most common types of penetrating sealers are silicates, silane-siloxanes, and siliconates. Silicate sealers will increase the strength of the concrete reducing deterioration caused by surface abrasion but have minimal pore-filling properties. Silane-Siloxanes and Siliconates are water repellents. They help reduce staining and deterioration caused by water absorption. They reduce staining by slowing down the movement of water through the substrate, but they don’t leave a protective surface film blocking the stain-producing material.

If you want to stop oil from staining the concrete, you need to use a film-forming coating. Acrylics, epoxies, and urethanes are types used to reduce staining. Acrylic sealers can be used to seal interior and exterior concrete because they breathe, allowing vapor to pass through them. Epoxy and urethane coatings should only be used to seal interior concrete. They trap moisture vapor in the slab which could cause a freeze-thaw issue.

• Acrylic Sealers:
  • Acrylics will provide up to 2-10 hours of protection against oil before the oil starts to degrade the film.
• Epoxy Coatings:
  • Epoxies provide more protection than acrylic sealers, but less than urethane. Interior applications only.
• Urethane Coatings:
  • Urethanes provide the most protection against oil. Interior applications only. They buy you the most time to clean up the oil. Urethane coatings are commonly used in automotive repair facilities.

Maintenance Plans

If stains are undesirable, it’s recommended to set up a cleaning schedule using professional-grade methods and supplies. The longer oil is in contact with the substrate, the greater the chance stains will develop.

In an automotive repair facility, daily cleaning should be scheduled. Having a process during the day to remove an oil spill as soon as it happens will reduce potential staining.

On a large floor, an auto-scrubber with a detergent is the most efficient. Induce the detergent concentrate into the clean water tank. As the auto-scrubber moves across the floor, water will be sprayed onto the surface. Brushes or pads fitted to the machine will agitate the cleaner and debris, allowing it to be removed more easily. At the rear of the machine is a squeegee. After the contaminated water has been extracted, the floor dries very quickly, leaving a clean surface.

If an auto-scrubber is not available, a mop and bucket will work. It is not very efficient and can be very time-consuming. The same detergent can be added to the water. A rayon mop is used to put material on the floor and a cotton mop is used to pick up material. In this case, a cotton mop should be used. The water needs to be changed regularly. It might take multiple applications.   

Conclusion

When trying to remove an oil stain from a concrete surface, selecting a mechanical or chemical method is the first step. If altering the surface texture is a concern, selecting a chemical method will be the best choice.

The first step when using a chemical is to remove all the oil on the surface with a poultice material. This will rid the surface of oil and at the near surface. If the stain stays, select another method to address the area.

Niagara Machine has everything you need whether it be a mechanical method or chemical. Do a little research on which method will work best and then give us a call!