How to remove oil from concrete

How to remove grease and oil from concrete

1. 1

   Blot and cover a fresh spill

   Wipe up any pooled oil with rags or paper towels, then pour a thick layer of clay cat litter, sawdust or baking soda over the spot and leave it to soak up the oil.

   Why: Oil penetrates concrete quickly. A dry absorbent pulls up what hasn't soaked in yet, before it spreads through the pores.

2. 2

   Sweep up and dispose of the absorbent

   Sweep the oily absorbent into a bag and throw it out with household trash, or follow your local rules for oily waste. Scrape off any thick grease with a putty knife.

   Why: Grease mostly sits on the surface, so scraping removes the bulk. Oily absorbent left outside washes into the street when it rains.

3. 3

   Scrub with detergent or a degreaser

   Wet the spot lightly, sprinkle on powdered laundry detergent or squirt dish soap, and scrub hard with a stiff nylon brush. For older stains, use a concrete degreaser instead and follow its label for dilution and dwell time.

   Why: Surfactants surround oil droplets so they can be carried off by water. Degreasers are concentrated alkaline soaps that loosen oil held deeper in the pores.

4. 4

   Rinse sparingly and collect the water

   Rinse with a small amount of hot water and soak it up with more absorbent or a wet/dry vacuum. Don't hose oily, soapy water down the driveway into the street.

   Why: The EPA notes that storm drains carry runoff untreated to streams and lakes, so oil and detergent rinsed into them end up in waterways.

5. 5

   Poultice an old or stubborn stain

   Saturate cat litter or sawdust with acetone or lacquer thinner and spread it over the stain about ¼ to ½ inch thick, extending an inch past the edges. Cover with plastic sheeting taped at the edges and let it work for 24 to 48 hours, then scrape it off and repeat if the stain is lighter but still visible. Work outdoors or with the garage door open, away from flames.

   Why: The solvent dissolves oil inside the concrete, and as the poultice dries, the absorbent draws the dissolved oil up out of the pores. Without the absorbent, the oil would just spread wider. The thickness and timing follow the Natural Stone Institute's poultice method.

6. 6

   Let it dry before judging

   Let the concrete dry completely before deciding whether to repeat.

   Why: Wet concrete looks darker than dry, and a freshly cleaned patch can look like a new stain at first.

Why oil soaks into concrete

Concrete is made with portland cement, and hardened cement has a huge internal surface area full of tiny pores. Motor oil and cooking oil are oil stains: non-polar liquids that water can't dissolve. They wick into those pores on contact and darken the surface from within.

That's why surface cleaners often seem to work and then the stain "comes back" as the concrete dries. The cleaner shifted the oil around but didn't lift it out. Absorbents and poultices work the other way: they pull oil up out of the pores into something you can sweep away. Thick grease is different. The Canadian Building Digest on concrete stains notes that grease doesn't penetrate far, so it mostly needs scraping and scrubbing.

Why acid and pressure washers aren't the answer

Muriatic (hydrochloric) acid is often sold for cleaning concrete, but it dissolves the cement surface and doesn't dissolve oil. New Mexico State's extension guide warns that it etches concrete away. Pressure washers can also etch the surface if set too high or held too close, leaving a rough patch that's more visible than the original stain.

Older technical guides suggested poultices made with benzene-type solvents or caustic soda. Those are hazardous, and acetone or lacquer thinner in an absorbent is the more common household approach today.

By situation

Fresh oil drip from a car

Absorb it right away. A fresh drip often disappears with cat litter followed by a detergent scrub. Slide a drip pan or piece of cardboard under the leak until it's repaired.

Old, dark oil stains on a driveway

Expect several rounds. Scrub with a concrete degreaser first, then poultice what's left. For heavily soaked or very old stains, commercial products that use oil-eating microbes are another option, used according to the label. Some old stains only lighten.

Cooking oil or grease on a patio

Grill grease and food oils respond to the same order: absorbent, then dish soap or a degreaser with hot water and a stiff brush. Dish soap is made to cut food fats, so it's a good first choice here.

Sealed, colored or stamped concrete

Test any cleaner in a hidden spot first, and follow the coating or sealer maker's directions. Solvents can soften some sealers. Once the stain is out and the concrete has dried for a few days, the area may need resealing.

Garage and basement floors with coatings

Epoxy and other floor coatings keep oil on the surface, so wipe it up and wash with detergent. Don't use solvents or degreasers on a coating without checking the coating maker's directions.

What not to do

• Don't use muriatic acid on an oil stain. It etches away the concrete surface and doesn't dissolve oil, so you get a rough, discolored patch.
• Don't use gasoline, lighter fluid or other fuels as a degreaser. Extension guidance warns against fuels as cleaning solvents because of the extreme fire danger, and they add more oil.
• Don't scrub with a wire brush. It can leave small steel particles in the concrete that rust and cause a new stain.
• Don't hose oily wash water into the street or a storm drain. Storm drains flow untreated to streams and lakes.

Other methods that work

Baking soda or detergent paste

A paste of baking soda or powdered laundry detergent and water, scrubbed in with a stiff brush and left a while before rinsing, handles light and fresh stains without stronger chemicals.

Caution: It won't reach oil that has soaked deep into the pores.

Oil-eating microbial cleaners

Bioremediation products contain microorganisms that break down hydrocarbons over days to weeks. They're an option for large, old stains where solvents haven't worked.

Caution: Follow the label closely. They work slowly and need the right moisture and temperature.

Pressure washing

Hot-water pressure washing with a degreaser can lift surface oil from large areas.

Caution: Too much pressure or holding the nozzle too close etches the surface, and the runoff still has to be kept out of storm drains.

Stain still there?

The stain came back after the concrete dried

Oil deeper in the pores wicked back up to the surface. Use a poultice rather than more scrubbing, and repeat until a fresh poultice no longer darkens.

There's now a light, clean patch around the stain

That's the rest of the driveway's normal grime. It usually blends over time, or you can clean the whole slab with detergent for an even look.

The poultice dried without lifting anything

It may have dried out before the solvent could work. Cover it tightly with plastic so it stays damp longer, and make sure the absorbent is fully saturated.

Safety

• Acetone and lacquer thinner are highly flammable: work outdoors or with doors open, with no flames, pilot lights or sparks nearby.
• Wear gloves and eye protection with degreasers and solvents.

Never mix cleaning products; see chemicals you must never combine.

Questions

Grease and oil on other surfaces

• Grease and oil stains: the complete guide
• Grease and oil on carpet
• Grease and oil on clothes
• Grease and oil on hair
• Grease and oil on leather
• Grease and oil on suede

Other stains on concrete

• How to clean concrete