Concrete and asphalt are often used together to create a versatile driveway, patio, sidewalk, or garage area. 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’ll explore them in this guide.
How Do Asphalt Stains Happen on Concrete?
Professional hardscapers tend to install asphalt after concrete. They heat it to high temperatures to liquify the tar content and allow it to flow more easily. It’s not unusual for overspray or drippage to happen near the official “seam” where the asphalt meets the concrete.
Unless preparations are made in advance to protect the concrete surface, the 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 the asphalt stays on the concrete, the harder it becomes 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. Which method you choose depends on the size of the area, the age of the stain, and the tools and materials available.
Pressure Washing
Pressure washing is often the first line of defense against asphalt stains on concrete, since most other methods involve deep cleaning anyway. Many times, if the asphalt is relatively new, the tar will still be somewhat pliable, making a blast of water particularly effective. It’s also a safer method for both you and the concrete, since 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 completely remove chunks of cured asphalt, but surface stains may still 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
Interestingly, one of the best solvents 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 the concrete. In most situations, repeating this process as needed will return the concrete to its normal appearance. However, if the stain is particularly difficult to loosen, you may need to use more powerful chemicals.
Mineral Spirits and Other Solvents
For more stubborn asphalt stains, solvents like mineral spirits or turpentine can be effective. These chemicals break down the oil in the asphalt and make it easier to remove from the concrete surface.
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 away. There’s less elbow grease required, but at the cost of more safety risks. These chemicals are caustic, so they can cause serious burns on contact with eyes and skin. They can also irritate the lungs, so a respirator is essential.
Concrete Cleaner
Concrete cleaners usually consist of a chemical agent designed specifically for breaking 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. This method can be used to not only clean concrete but also change the 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. A solution of muriatic acid diluted with water is applied to the surface, allowed to foam up, and rinsed away with water.
However, there may be situations where the ability to neutralize the acid is needed, such as with accidental spills and drips. Readily available products like baking soda and lime are very effective at neutralizing muriatic acid, so it’s a good idea to have some around before using this method.
Unconventional Methods
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, cat litter can be used to absorb the majority of the oil. This 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
In most situations, 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 will often dictate which method is required to do a professional job. Just remember to try the simplest method first and only employ more aggressive methods as needed.
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