Maybe it's the drip spot where the old truck sat all winter. Maybe it's a dark shadow on the garage floor that came with the house. Or maybe you just kicked over the drain pan.
Spring is when most people notice. The snow melts, the slab dries out, and every drip from November through March is sitting there on light gray concrete. Here's what gets it out, and what makes it worse.
Why Oil Hangs On So Hard
Concrete is full of tiny pores and acts a lot like a hard sponge. Oil soaks in and spreads below the surface, where a hose can't reach it.
- The clock is running. A puddle still sitting on top can mostly be lifted off. Give it a few weeks and much of it is inside the slab.
- Old stains creep back. Scrub the surface and oil deeper down can wick back up over the next few days. The methods that work pull oil out instead of just washing the top.
Match the Method to the Stain
| Stain age / type | What to use | What to expect |
|---|---|---|
| Fresh puddle (minutes to a day old) | Blot, then cat litter or sawdust, then dish soap and hot water | Usually gone or close to it |
| Drip spot, weeks to months old (motor oil, transmission fluid) | Degreaser scrubbed in, rinsed, repeated | Much lighter; may leave a faint shadow |
| Old, set-in stain (a year or more) | Poultice, repeated, or a microbial cleaner over several rounds | Noticeably lighter. Full removal isn't guaranteed. |
| Thick grease (bearing grease, chassis lube) | Scrape off the solids first, then degreaser | Good, once the bulk is off |
| Gas or diesel drip | Absorbent, plenty of fresh air, nothing that sparks nearby, then a detergent wash | Gas mostly evaporates. Diesel behaves more like oil. |
| Antifreeze (not actually oil) | Absorbent, then soapy water | Usually comes out. Clean it up fast: the common kind tastes sweet and is poisonous to pets and kids. |
Fresh Spill: The First Hour
Don't reach for the hose. Oil floats on water, so hosing spreads it wider and carries the sheen toward the street.
- Get the liquid off the surface. Soak up anything still pooled with old rags or shop towels, lifting rather than smearing.
- Let an absorbent pull out the rest. Plain clay cat litter (unscented, non-clumping), sawdust, diatomaceous earth, or the granular oil absorbent sold at auto parts stores all work. Spread it thick and past the edges, crush it into the surface texture with a boot heel or a brick, and leave it at least a few hours, overnight if you can. If the granules come up dark when you sweep, do another round.
- Wash what's left with dish soap, hot water, and a stiff nylon brush. Soak up the dirty water with a wet/dry vacuum or more absorbent instead of hosing it away.
Set-In Stains: Pick the Tool for the Job
Once oil is in the pores, you need something that loosens it and gives it a way out.
For a driveway you don't want to fuss over: a microbial cleaner
These pair a detergent with microbes that digest petroleum, and the microbes keep working in the pores after you rinse. They're slow and take several applications, but there are no fumes. Look for "microbial" or "bacterial" on the label (enzyme cleaners target food and pet messes instead), and don't follow up with bleach, which kills the bacteria you just paid for.
For one dark, deep spot: a poultice
A poultice is a paste that draws oil out as it dries. Mix a fine absorbent powder (diatomaceous earth, talc, whiting, or finely crushed clay litter) with mineral spirits or acetone until it's about as thick as peanut butter. Spread it a quarter to half an inch thick, past the stain's edges, cover it with plastic taped down, and leave it about a day. Then uncover it, let it dry, and scrape it off. Heavy stains can take two or three rounds; wash off the residue between rounds.
Solvent poultices are flammable. Work outdoors or with the garage door wide open, never near a gas water heater or furnace. To skip the fumes, mix a strong alkaline degreaser into the powder instead.
For a big area of drips: degreaser and a stiff brush
Water-based concrete and engine degreasers break oil up so you can scrub it loose and rinse it away. Wet the area, apply, work it in hard, let it sit for the labeled time without drying, then rinse and repeat. Dish soap is usually too weak for set-in oil. Stronger alkaline degreasers do more, and they're caustic: wear gloves and eye protection, and keep them off your plants.
To finish: pressure washing with a degreaser
A pressure washer is the last step, not the first. Pre-treat, let it dwell, scrub, then rinse. On its own, it moves oil around more than it removes it.
Too much pressure, the wrong tip, or holding the wand too close etches the surface and leaves stripes. A rotary surface cleaner gives a far more even result. Catch the runoff, too: storm drains generally carry water straight to creeks and rivers without treatment. And since a cleaned spot often looks lighter than the weathered concrete around it, clean the whole slab if you want an even look.
What Doesn't Work (and What Makes It Worse)
- Hosing it off. Water and oil don't mix. You'll just spread the stain.
- Chlorine bleach. It isn't a degreaser. And never mix bleach with ammonia or acids (including some concrete and rust cleaners). Those combinations give off toxic gases.
- Muriatic or other strong acids. Acid doesn't dissolve oil. It eats the cement paste instead, leaving a dark stain inside a rough, etched halo.
- Pouring gasoline or thinner on it and walking away. It's a fire hazard, and a thin liquid can carry oil deeper and wider. A poultice works because the powder pulls the solvent and oil back out.
- Painting over it. Oil keeps paint from bonding, so it peels right where the stain is.
Why Sealed and Coated Concrete Shrugs Off Oil
Bare concrete drinks oil because its pores are open. Close them and spills sit on top long enough to clean up.
| Surface | How it handles oil | The catch |
|---|---|---|
| Penetrating sealer (silane/siloxane) | Slows absorption and buys time to wipe up | Built mainly to keep out water and salt, not oil. If oil is the concern, look for a label that claims oil and stain repellency. |
| Film-forming acrylic sealer | Spills sit on the surface film | Wears faster, can get slick, and hot tires can pull it up |
| Garage floor coating (epoxy, polyurethane, polyaspartic) | A continuous, non-porous layer. Drips sit on top and wipe up. | Only as good as the prep. Wipe spills promptly, since some fluids and solvents can stain or soften some coatings if left sitting. |
In a garage, a floor coating ends the drip-stain cycle: oil, salt brine, and road grime land on the coating instead of in the concrete. But oil already in the slab is one of the most common reasons a coating won't bond. Our coating prep includes degreasing stained areas and grinding the surface, and we check for remaining oil before anything goes down.
Two-minute check: Sprinkle clean water across the floor. Clean concrete darkens as it soaks the water up. Spots that stay light, or where the water beads, still have oil in them and need attention before a sealer or coating goes on.
Outdoor sealer also needs clean, dry concrete. If you're having slabs lifted and joints caulked too, the order is clean, dry, lift, patch the holes, caulk, and seal once the caulk has cured. More in why seal concrete.
Getting Rid of the Oily Mess
The Wisconsin DNR allows oil absorbents to go to a landfill as long as no free-flowing oil is visible in or on them and they aren't otherwise hazardous waste. For most homeowners, that means well-drained litter can be bagged for the trash, but your municipality or hauler can be stricter, so check first.
- Used motor oil never goes in the trash. Wisconsin bans it from landfills. Stores that sell motor oil must either collect it or post a sign saying where you can.
- Solvent-soaked poultice waste is flammable. Keep it sealed, outdoors, away from anything that sparks, and ask your county's household hazardous waste program how to get rid of it.
- Never sweep oily litter or rinse water into a storm drain.
When You Don't Need Us (and When You Might)
A fresh spill or a couple of drip spots? Handle it yourself. You don't need to hire anybody for that.
Send us photos if the whole driveway or garage floor has years of drips and you want it cleaned evenly, if you plan to seal afterward, or if you're considering a garage floor coating, where dealing with old oil is part of our prep.
Straight talk: no cleaning method can promise a decades-old oil stain will disappear completely. From your photos, we'll tell you what's realistic before you spend anything.