Concrete

What Is Efflorescence on Concrete?

The white powder is salt left by evaporating water. Causes, and how to remove it.

Reviewed July 2026

Efflorescence is the white, powdery or crystalline film that appears on concrete, brick, and block. It is not mold, not a stain, and not a defect in the material itself: it is salt, left behind when water moves through the masonry and evaporates at the surface. Understanding that one mechanism explains both why it shows up and how to deal with it.

What the white deposit actually is

Concrete and masonry contain water-soluble salts, and cement hydration itself produces calcium hydroxide inside the concrete. When moisture moves through the material, it dissolves these salts and carries them along. At the surface the water evaporates, but the dissolved salts cannot evaporate, so they are deposited as a visible white residue. Much of the classic white bloom is calcium carbonate, formed when calcium hydroxide reaches the surface and reacts with carbon dioxide from the air, the same carbonation reaction that turns a fresh concrete surface faintly chalky.

It always takes water

Efflorescence needs three things at once: soluble salts in the material, water to dissolve and move them, and a surface where the water can evaporate. Concrete and masonry supply the salts, so the variable is water. That is why efflorescence tends to appear on new concrete as it dries out, on basement and retaining walls where ground moisture pushes through, and after wet weather. Where there is no moisture movement, there is no efflorescence, which is what makes it controllable.

Cosmetic, but a useful warning

The deposit itself is generally harmless to the structure and mostly an appearance issue. Its real value is as a signal. Efflorescence tells you water is actively moving through the material, and sustained moisture, not the salt, is what drives the freeze-thaw damage, spalling, and reinforcement corrosion that shorten concrete's life. So while you can scrub the white off, the more important response is to ask where the water is coming from.

How to remove it

For light, fresh efflorescence, dry brushing with a stiff brush often lifts it, since new deposits are loosely bound; follow with clean water and let the surface dry. Heavier or older deposits may need a proprietary efflorescence remover or a carefully diluted acid wash, always used per the manufacturer's directions, with eye and skin protection, and tested in a small area first because acids can etch and discolor concrete. Pressure washing can help but also drives more water in, which can bring more salt out later.

Keeping it from coming back

Because water is the driver, lasting control means managing moisture: improving drainage so water flows away from slabs and walls, sealing the surface with a breathable masonry sealer once it is clean and dry, and fixing the leaks or ground-water paths feeding it. Remove the deposit and you fix today's appearance; cut off the water and you fix the cause. For how moisture and salt reaching embedded steel leads to bigger trouble, see why concrete cracks.

Materials Review is an independent educational resource. It is not affiliated with Pittsburg State University or the former Kansas Polymer Research Center, and it is not a substitute for a licensed engineer. Confirm structural, safety, and code questions with a qualified professional before acting.