By Bennett's Concrete and Excavation, Norwich, NY. Updated October 2026.
What efflorescence is
The U.S. General Services Administration's preservation guide defines it as white deposits on the surface of concrete. Soluble compounds in the concrete or in the soil dissolve in water, travel to the surface and stay there when the water evaporates. Wausau Tile describes the same thing as a chalky mineral deposit, and notes it's typically not a concern for the concrete's structure.
Fix the stain and leave the water source alone, and it tends to come back.
Where it shows up
- Basement floors and foundation walls, where ground moisture moves through
- Steps, stoops and retaining walls with soil behind them
- Slabs near downspouts or where water ponds
- New concrete in its first months as it dries out
- Pavers and block as well as poured concrete
Make sure it's efflorescence
A few other things leave white marks:
- Road salt residue tracked in by cars, mostly in tire paths on aprons and garage floors. It rinses off with water.
- Discoloration from finishing or curing, which NRMCA's guide on discoloration covers. It shows as light and dark patches in the surface itself rather than powder on top.
- A failing sealer that has turned cloudy.
Efflorescence is a dry powder or crust that you can usually brush or scrape off.
How to remove it: start gentle
- Dry brush. Wausau calls a dry brush or rotary scrubber the simplest way to clear it. Do this first, on a dry day.
- Rinse lightly and dry completely. Wausau warns that if the surface isn't dried fully, the efflorescence can come back.
- Use a mild acid cleaner if needed. Commercial efflorescence cleaners with a weak acid work on stubborn deposits.
On new concrete, give it time
New slabs often show a white bloom in the first months as water leaves the concrete. Before reaching for acid, let the slab finish curing and drying, then dry brush it. Acid on young concrete can etch the surface you just paid for. If the haze keeps coming back in the same spot, look for the water source rather than cleaning harder.
On stamped and colored concrete, go even easier. Any acid can change the look of the color and the sealer, so test first and ask your installer what their sealer can take.
Using acid safely
For heavier deposits, the GSA procedure uses dilute acid on concrete that has first been soaked with clean water:
- 1 part hydrochloric (muriatic) acid in 9 to 19 parts water, or
- 1 part phosphoric acid in 9 parts water
Apply with a stiff non-metallic brush, then rinse thoroughly with clean water. Always add acid to water, never water to acid. NRMCA's discoloration guide describes even milder options, such as a 1 percent muriatic solution or a 3 percent acid like white vinegar, flushed off within 15 minutes, and recommends testing any chemical on an out-of-sight spot first.
Acid etches concrete and can lighten colored or stamped concrete. Wear eye protection and gloves, keep it off plants and metal, and stop at the mildest method that works.
What not to do
- Don't pour straight muriatic acid on concrete. The GSA procedure uses it diluted at least 1 part in 9 parts water.
- Don't mix cleaning chemicals with each other.
- Don't apply a second chemical before the first is rinsed away. The GSA procedure is clear on that.
- Don't seal over efflorescence. Sealer locks the white haze in.
Stop it coming back
The long-term fix is less water moving through the concrete:
- Point downspouts away and fix grading so water runs away from slabs and walls. See grading away from your foundation.
- For new interior slabs, a vapor retarder under the floor keeps ground moisture out. See vapor barriers under slabs.
- Seal exterior concrete once it's clean and dry. Wausau notes a penetrating sealer makes concrete less permeable, which reduces, though doesn't fully prevent, efflorescence. Our sealing guide covers timing.
When it points to a bigger problem
Heavy, repeated efflorescence on a basement floor or wall means steady water. That's worth looking at before you finish the space. On the outside, it often traces to grading or a downspout dumping next to the house. Our crew handles regrading and drainage as well as cleaning and sealing, and our guide to basement floor replacement covers when a floor needs more than cleaning.
