Gasoline will dissolve tar from concrete, but it’s one of the worst solvents you could choose for the job. Tar and gasoline are both hydrocarbon-based, so gasoline does break down tar effectively on a chemical level. The problem is that gasoline creates serious fire, health, and environmental hazards that far outweigh its cleaning power, especially when safer solvents work just as well.
Why Gasoline Dissolves Tar
Tar (and its close relative, asphalt or bitumen) is a thick mixture of hydrocarbons held together by heavier molecules called asphaltenes, which are stabilized by lighter resin compounds. When you pour gasoline onto tar, the lighter hydrocarbons in gasoline dissolve those resins and destabilize the mixture, causing it to soften and break apart. This is the same basic chemistry that makes gasoline dissolve grease and oil. Like dissolves like, and both gasoline and tar sit on the hydrocarbon spectrum.
So yes, if you poured gasoline on a tar stain and scrubbed, the tar would come up. But in practice, you’d be trading one problem for a handful of worse ones.
The Fire Risk Alone Rules It Out
Gasoline has a flash point of negative 45 degrees Fahrenheit. That means it produces ignitable vapors at virtually any temperature you’d encounter outdoors. For comparison, charcoal lighter fluid doesn’t produce flammable vapors until 160 degrees. Gasoline is in a completely different risk category.
When you spread gasoline across a concrete surface, it evaporates quickly and creates a low-lying cloud of heavier-than-air vapor. A spark from a nearby tool, a pilot light from a water heater, even static electricity can ignite it. People routinely underestimate this risk because they associate fire danger with open flames, not invisible vapor spreading across a driveway.
Vapor Exposure Is a Real Health Concern
Scrubbing tar off concrete takes time, and the entire process keeps you hunched over a pool of evaporating gasoline. According to the CDC’s Agency for Toxic Substances and Disease Registry, gasoline vapors act primarily on the central nervous system. Even low concentrations can cause flushing, dizziness, slurred speech, mental confusion, nausea, and headaches. Higher concentrations can lead to unconsciousness, seizures, and respiratory failure.
Gasoline vapors also irritate the eyes, nose, throat, and lungs. In severe cases, exposure has caused pulmonary edema and hemorrhage in the airways. The vapors can also sensitize the heart muscle to irregular rhythms, a particularly dangerous effect that most people wouldn’t anticipate from a cleaning task. Working outdoors reduces the risk compared to a garage, but doesn’t eliminate it, especially on hot days when evaporation accelerates.
Gasoline Damages Concrete Over Time
Concrete is porous. When you pour gasoline onto it, the liquid doesn’t just sit on the surface. It soaks into the pores and can penetrate deep into the slab. Research on gas station concrete pads has found that over time, gasoline accumulates within the concrete and can eventually break through into underlying soil and groundwater. Even a single cleaning session can leave hydrocarbon stains that are harder to remove than the original tar.
You may solve the tar problem only to create a gasoline stain and a faint petroleum smell that lingers for weeks, particularly in enclosed spaces like a garage floor.
Environmental and Legal Issues
Any gasoline that runs off your concrete into a storm drain, gutter, or soil becomes a potential environmental violation. The EPA regulates hydrocarbon discharges that reach waterways, and even a small amount of petroleum can create a visible sheen on water surfaces, which triggers reporting requirements under the Clean Water Act. Residential use on a driveway may seem small-scale, but gasoline-contaminated runoff flowing into a storm drain connects directly to local waterways in most municipalities.
Safer Solvents That Work Just as Well
Several products dissolve tar through the same hydrocarbon chemistry as gasoline but with dramatically lower fire risk, less toxicity, and no damage to concrete.
- Mineral spirits: This is the most direct substitute. Mineral spirits dissolve tar effectively and have a much higher flash point than gasoline, typically around 105 to 115 degrees Fahrenheit. The vapors are less intense, though you should still work in a ventilated area. Apply mineral spirits to the tar stain, let it soak for 5 to 10 minutes, then scrub with a stiff brush.
- Citrus-based degreasers: Products containing d-limonene (the solvent compound in orange peel oil) break down tar without petroleum-based chemicals. They’re slower-acting but much safer to handle and produce pleasant-smelling, far less toxic fumes.
- Commercial tar removers: Hardware stores carry tar and asphalt removers specifically formulated for concrete. These are typically petroleum distillate blends with higher flash points and added surfactants that help lift dissolved tar off the surface so it can be rinsed away.
- WD-40 or diesel fuel: Both will soften tar in a pinch. Diesel has a flash point above 125 degrees Fahrenheit, making it considerably safer than gasoline, though it can leave its own oily residue that needs degreasing afterward.
How to Remove Tar From Concrete Safely
Start by scraping off as much solid tar as possible with a putty knife or floor scraper. The less tar the solvent has to dissolve, the faster the process goes and the less solvent you’ll need. For thick deposits, warming the tar with a heat gun makes it more pliable and easier to peel up, though be careful not to overheat the concrete.
Apply your chosen solvent generously to the remaining stain and let it dwell for 5 to 15 minutes. Scrub with a stiff-bristled brush, then wipe the dissolved tar away with old rags or paper towels. You may need to repeat this process two or three times for deeply set stains. Follow up with a strong degreaser or dish soap and hot water to remove any solvent residue from the concrete pores.
For stubborn stains that survive solvent treatment, a poultice method works well. Mix an absorbent powder (like diatomaceous earth or cat litter) with your solvent into a paste, spread it over the stain, cover it with plastic wrap, and let it sit overnight. The paste draws dissolved tar up out of the concrete as it dries.
Disposing of Tar-Contaminated Rags
Rags soaked with any petroleum-based solvent are a fire hazard. Don’t throw them in a trash can where they can heat up and spontaneously combust. Spread used rags flat outdoors to dry completely, weighted down so they don’t blow away. Once dry, store them in a metal container with a tight-fitting lid, submerged in water mixed with a grease-cutting detergent. Dispose of them at your local hazardous waste collection event. If you use solvent-soaked rags regularly, consider getting a proper oily waste container.