Efflorescence is the white, powdery or crystalline deposit that appears on concrete when moisture moves through it, dissolves natural salts, and evaporates at the surface, leaving the salt behind. It is cosmetic, not structural — the concrete is fine — but it can be unsightly, and it tells you moisture is moving through the slab.
It is most common on new concrete and masonry in the first months, and it tends to show up after wet weather. The good news: it usually cleans off, and a few precautions keep it from coming back.
What causes it
Three things have to line up: soluble salts in the concrete or the ground beneath it, water to dissolve and carry them, and a surface where the water evaporates. Fresh concrete has the most free salts and moisture, which is why efflorescence is worst when it is new. Poor drainage, a missing vapor barrier, and a high water-cement ratio all feed it.
How to remove it
Start with the gentlest method: let the surface dry, then dry-brush the powder off with a stiff brush. If that does not do it, scrub with water and a stiff brush. For stubborn deposits, a dilute efflorescence cleaner or masonry (muriatic) acid works — follow the product directions and wear eye protection, gloves, and a respirator, and rinse thoroughly. Never mix cleaning chemicals.
How to prevent it
Reduce the moisture moving through the slab: ensure good drainage away from the concrete, use a vapor barrier under interior slabs, and keep the water-cement ratio low so the concrete is denser. Once the slab has fully cured and any initial efflorescence is cleaned off, a breathable sealer helps keep it from returning.
Is it a problem?
On its own, no — efflorescence is a surface deposit, not damage. But persistent efflorescence signals ongoing moisture movement, which over years can contribute to other issues like spalling in freeze-thaw climates. Treat the moisture source, not just the white residue.
Common questions
What is the white stuff on my concrete?
Efflorescence — salt deposits left when moisture moves through the concrete and evaporates at the surface. It's cosmetic, not structural damage.
How do you get rid of efflorescence?
Dry-brush it first; then water and a stiff brush; then a dilute efflorescence cleaner or masonry acid with proper protection. Rinse well.
Will efflorescence go away on its own?
Early efflorescence often weathers away over a season as free salts deplete. Persistent deposits mean ongoing moisture — fix drainage and seal.