The short answer
The white staining on your concrete, some people describe it as a white fur or fuzz growing from the floor, is efflorescence: water moving through the slab dissolves salts, carries them to the surface and evaporates, leaving the minerals behind. It is cosmetic, but it is also a moisture report, persistent efflorescence means water is moving through the concrete and is worth investigating before coating or sealing anything over it.

What efflorescence is
Efflorescence is the chalky white deposit that appears on concrete, brick and parging, when it crystallizes it can even look like a white fur or fuzz growing out of a basement floor. It forms when water moves through the material, dissolves soluble salts inside, and carries them to the surface, where the water evaporates and leaves the salt behind. It is cosmetic in itself, but it is a reliable sign that water is moving through the concrete.
Why it matters
The deposit is harmless, but the moisture behind it is not. The same water travel that leaves efflorescence also feeds freeze-thaw damage and, over time, corrosion. Persistent efflorescence on a foundation wall, a slab or parging is worth tracing to its source (grading, a downspout, or moisture from below) rather than just wiping off.
How to deal with it
Light efflorescence often brushes off dry or rinses away; heavier deposits may need a proper efflorescence cleaner. But cleaning treats the symptom. The lasting fix is addressing the water: correct the grading or downspout, repair cracks letting water in, and seal the surface so moisture stops migrating through. On a coating or paint job, dealing with efflorescence and moisture first is what stops the finish from failing later.
Key takeaways
- Efflorescence is mineral salt left behind by water moving through concrete.
- The deposit is cosmetic; the moisture behind it is the real signal.
- Cleaning removes it; fixing drainage and sealing keeps it from returning.
- Recurring efflorescence is worth tracing to a water source.
Frequently asked
Is efflorescence the same as mould?
No. Efflorescence is a mineral salt deposit and brushes off as powder; mould is biological. If white deposits keep returning, the issue is water movement, not mould.
Will sealing stop it?
Sealing helps by reducing water migration, but only after the water source is addressed, sealing over an active moisture problem can trap it.
