Every spring the snow pulls back and shows you what your concrete went through: leaf outlines on the patio, a white crust inside the garage door, black tire streaks, a splash of paint from last summer's fence project.
Most of it comes off. Some of it isn't a stain at all.
Oil, rust, and mold each have their own guide: how to clean oil off concrete, how to remove rust from concrete, and how to clean mold off concrete. This one covers everything else.
Stain or Damage? Check Before You Scrub
No cleaner can put back concrete that's gone. Run your hand over the spot and look closely.
- Smooth, same texture as the rest, just a different color: a stain. Keep reading.
- Rough or sandy, with the top skin flaking off: scaling, usually from freeze-thaw and deicers.
- Chunks or deeper pieces missing: spalling.
- Small cone-shaped pits: popouts.
- A pale, rough, slightly sandy patch, often where a cleaner, fertilizer, or acid sat: etching. The surface paste was chemically eaten away.
- White, crusty, or powdery: salt residue or efflorescence. Both clean up, but read their sections first.
Then scrape the edge with a key. If concrete crumbles off, it's damage. Our guide to concrete spalling causes covers why it happens and your options. Cleaning and sealing can slow it down, but won't make a scaled surface look new.
Ground Rules for Any Stain
- Start mild. Water and a stiff nylon brush, then dish soap, then a targeted cleaner.
- Test a hidden spot, especially on colored, stamped, or sealed concrete.
- One product at a time. Rinse thoroughly before trying the next.
- Never mix bleach with ammonia or acids. Those combinations give off toxic gases. Vinegar, rust removers, and many masonry cleaners are acids.
- Keep runoff out of storm drains. They generally carry water to creeks and rivers without treatment.
- Go easy with a pressure washer. Too much pressure or the wrong tip etches the surface and leaves stripes. A rotary surface cleaner gives a more even finish.
Stain, Test, Treatment
| Stain | Quick test | Treatment |
|---|---|---|
| Leaf / tannin prints | Brown outline shaped like a leaf; surface is smooth | Oxygen bleach solution, dwell, scrub, rinse. Repeat for dark prints. |
| Tire marks | Black streaks where you turn or park; a rag with degreaser smudges them | Degreaser and a stiff brush, then rinse |
| Latex (water-based) paint | Softens with warm, soapy water | Fresh: soap and water. Dried: plastic scraper, then a stripper labeled for concrete or masonry |
| Oil-based or spray paint | Doesn't soften with water | Solvent-based stripper, or a solvent poultice for paint that soaked in. Ventilate well. |
| Efflorescence | White powder or crust near cracks, edges, or damp spots; powder brushes off when dry | Dry brush first. Hardened crust: efflorescence remover. Then fix the water source. |
| Salt / deicer residue | White haze or a damp-looking film, worst by the garage door and along walks after winter | Rinse with plenty of water and scrub; diluted white vinegar for stubborn haze, then rinse |
| Fertilizer | Orange dots mean iron. Pale, rough spots mean surface damage. | Orange: rust remover (see the rust guide). Pale and rough: not a stain. |
| Grill grease | Dark, slick spot under the grill; water beads on it | Fresh: dish soap and hot water. Set in: degreaser or poultice (see the oil guide). |
| Food, drink, pet accidents | Colored, smooth, sometimes smells | Oxygen bleach or an enzyme cleaner, scrub, rinse |
| Gum, tar, tree sap | Sticky or raised | Harden gum with ice and scrape. Mineral spirits for sap or tar, then soap and water. |
Leaf and Tannin Stains
Leaves contain tannins, the same kind of compound that stains a teacup. When rain soaks a fallen leaf, tannins wash out and leave a brown silhouette, most visible on light concrete. Up here, the darkest ones often show up at spring melt, from leaves that sat under snow all winter.
Oxygen bleach is the right tool. It's sodium percarbonate, a powder that releases hydrogen peroxide when it dissolves and breaks down to water, oxygen, and soda ash. Mix it in warm water per the label, apply it to wet concrete, keep it wet while it works, scrub, and rinse. Dark prints may take two rounds.
To prevent them, clear leaves off the concrete before rain soaks them.
Tire Marks
Black marks on bare concrete are rubber residue. A degreaser and a stiff brush handle most of them.
On sealed decorative concrete, look closer. If the "marks" are patches where the sealer pulled loose and stuck to the tires, that's hot tire pickup. It's mostly a bonding problem, and acrylic sealers are more prone to it than the cross-linked epoxy and polyurethane coatings used on garage floors. The fix is stripping and resealing, not scrubbing, and that's decorative-sealer work we refer to a specialist.
Paint
Speed and paint type decide this one. Wet latex comes up with soap, warm water, and a brush. Dried latex needs a plastic scraper and then a stripper labeled for concrete or masonry; a careful pressure wash sometimes lifts the rest. Oil-based and spray paint need a solvent-based stripper, or a solvent poultice if the paint soaked in, with the garage door wide open. Pigment that soaked into the pores can leave a faint ghost.
A safety note: since late 2019, paint strippers containing methylene chloride can't be sold to consumers for paint removal, after people died from the fumes. If an old can is still sitting on a garage shelf, take it to household hazardous waste instead of using it.
Efflorescence: White Deposits That Are Telling You Something
Efflorescence is a white, powdery or crusty deposit of salts that were dissolved in water inside the concrete. The water carries them to the surface and evaporates, and the salts stay behind. The main culprit is lime from the cement, which reacts with carbon dioxide in the air and turns into calcium carbonate. That's why it starts out powdery and gets harder to remove the longer it sits.
New concrete often blooms in its first months, and that usually fades. Efflorescence that keeps coming back is the kind to pay attention to, because it means water is still moving through the concrete. Check for downspouts or sump discharge dumping next to the slab, grading that sends water toward it, open joints or a gap along the house letting water underneath, and moisture coming up from below on basement and garage floors.
To remove it, dry brush first. Use a stiff brush on dry concrete and sweep or vacuum up the powder. Don't flood it with water, which can redissolve the salts and pull them back in. If it has hardened into a crust, use an efflorescence remover (a mild acid product): pre-wet the area, keep the dwell time short, scrub, and rinse thoroughly. Then fix the water, or it'll be back.
On a garage floor headed for a coating, this matters: moisture moving up through the slab is a well-known cause of coating failure, which is why we check for it during prep. Outdoors, don't seal concrete that's still blooming. Fix the water first, then use a breathable penetrating sealer, which lets moisture escape instead of trapping it under a film.
Salt Residue
That white haze along the walk and inside the garage door is deicer residue. Rock salt leaves a dry white film. Calcium and magnesium chloride pull moisture out of the air, so their residue can stay damp-looking or greasy long after the snow is gone.
Rinse it off with plenty of water and a stiff brush on a mild winter day and again in spring, flushing the joints. Diluted white vinegar and a good rinse usually lift a stubborn haze.
If the concrete under the haze is rough and flaking, that's salt damage, not just residue. And skip any deicer made with ammonium nitrate or ammonium sulfate. Both attack the concrete surface.
Fertilizer, Grill Grease, and Food
- Fertilizer: orange specks are iron, so treat them as rust. Pale, rough spots where granules sat are surface damage from ammonium-based fertilizer, not a stain. Sweep granules back onto the lawn right after spreading.
- Grill grease: treat it like oil. A grill mat prevents the next one.
- Food, drink, and pet accidents: oxygen bleach handles coffee, wine, berries, and pop. Enzyme cleaners break down the proteins, fats, and starches in food and pet messes, odor included.
When We're Worth a Call
Most single stains are a Saturday-morning job. You don't need us for a few leaf prints or a paint drip.
Send photos if you want the whole slab cleaned evenly (spot-cleaning often leaves a lighter patch), if there's a mix of stains you'd rather have handled at once, or if you want it sealed afterward so the next spill cleans up easier (see why seal concrete). On a garage floor, surface stains come off during coating prep, and a garage floor coating keeps new ones on top where they wipe up.
If your photos show scaling or spalling instead of stains, we'll tell you straight that cleaning won't fix it.