DIYers often pair concrete and asphalt to create a versatile driveway, patio, sidewalk, and garage areas. If asphalt accidentally comes into contact with a concrete surface, it can lead to unsightly stains or potential damage. However, there are a few effective ways to remove the asphalt. We explore them in this guide.
How Do Asphalt Stains Happen on Concrete?
Professional hardscapers typically install asphalt after concrete. They heat the asphalt to high temperatures to liquefy the tar content and allow it to flow easily. It’s not unusual for overspray or drippage to occur near the official seam where asphalt meets the concrete.
Unless hardscapers make preparations in advance to protect the concrete surface, oil in the asphalt can seep through cracks and pores on the concrete’s surface. Even after the solid asphalt gets removed, pesky and unsightly stains can still remain, and sealers and stains can’t penetrate through them, harming the concrete’s finish in the end.
The longer asphalt stays on the concrete, the harder it is to remove. It’s best to address fresh stains as soon as they happen or as soon as you notice them.
What Methods Can I Use to Remove Asphalt From Concrete?
Some ways to remove asphalt stains are gentle and non-toxic, while others are more intense and use strong chemicals. The best method depends on the size of the area, age of the stain, and the tools and materials you have available.
Pressure Washing
Pressure washing is often the first line of action against asphalt stains on concrete because most other methods involve deep cleaning anyway. If the asphalt is relatively new, the tar will be pliable, making a blast of water effective. It’s also a safer method for both you and the concrete: you can often avoid using caustic chemicals.
Many pressure washers can run at a high enough setting to damage the concrete, so only use high-pressure tips as needed. Instead, do multiple passes over the area with a less aggressive spray tip.
Pressure washing also works to remove all of the chunks of cured asphalt, but surface stains may remain. A professional hardscaper may use detergents to dissolve the remaining residue and do another set of passes over the area.
Soap and Other Detergents
One solvent for dissolving the oil in asphalt is soap. Soaps and detergents are readily available, do a great job of breaking down the oil, and will not harm concrete. In most situations, repeating this process as needed will return the concrete to its normal appearance. However, you may need to use more powerful chemicals on stubborn stains.
Mineral Spirits and Other Solvents
For hard-to-remove asphalt stains, solvents like mineral spirits and turpentine can work. These chemicals break down the oil in the asphalt, making it easier to remove.
A professional will apply the solvent directly to the surface, let it sit for a few minutes to a few hours, and clean the stain. There’s less elbow grease required but safety is an issue. These chemicals are caustic and cause serious burns when they contact the eyes and skin. They can also irritate the lungs, so you should use a respirator when you work with them.
Concrete Cleaner
Concrete cleaners often consist of chemical agents designed to break down oil stains on concrete. They aren’t used often for large chunks but are effective at removing the residue left behind in conjunction with pressure washing.
Concrete Etching Solution
A more abrasive way to remove asphalt from concrete involves the use of very strong chemicals to break down not just the stain but the top layer of concrete as well. You can use this method to clean concrete and change its texture.
Concrete etching solution usually includes some form of hydrochloric acid, which is extremely caustic. Protective clothing and safety gear (including a respirator) are required when using this type of solution, as it will cause severe burns.
Muriatic Acid
Muriatic acid will dissolve most materials, such as metals, plastics (with exceptions), and finishes, which is why it is so effective in removing asphalt. Apply a solution of muriatic acid diluted with water to the surface. Allow it to foam up, then rinse it away with water.
You may encounter situations in which you need to neutralize the acid, such as with accidental spills and drips. Baking soda and lime, two readily available products, can neutralize muriatic acid, so it’s a good idea to have some around before using this method.
Unconventional Methods to Remove Asphalt From Concrete
There are also common products and solvents that are known to be effective in removing asphalt stains from concrete. These common household items are effective and generally safe to use, especially if the stains are light. Navigate the tabs below to see how they work:
If the stain is relatively new and still somewhat liquid, you can use cat litter to absorb the majority of the oil. This technique often makes removing the stain much easier because when the stain is still liquid, it can make the stain larger. Removing the oil keeps the stain from flowing and making the job more involved.
Oven cleaners are designed to dissolve burnt food waste and are quite caustic. This method can work to dissolve thicker stains if applied and allowed to work for a few hours, especially in direct sunlight. Care should be taken to wear protective gloves and eyewear when using this method, however, because these cleaners are very strong and can damage unprotected skin.
Surprisingly, cola has been used to remove, or at least soften, asphalt stains on concrete. The carbonation of cola tends to soften most stains and will not damage the concrete surface. If the stain is light, several applications of cola and light brushing can lighten an asphalt stain to the point of being unnoticeable.
Patience and Safety Is Key
Many times, removing asphalt stains from concrete will require a combination of patience, trial and error, and elbow grease. The age, thickness, and size of the stain often dictates which method can do the most professional job. Try the simplest method first and only employ more aggressive methods as needed.
