Efflorescence: the white powder on brick and render
25 June 2026 · 3 min read
White crystalline deposits on masonry are a symptom, not a stain. What causes them, when they stop on their own, and why brushing is better than washing.
White, crystalline, sometimes fluffy deposits on brick, render or mortar. It looks like the wall is growing something. It is salt, and it is telling you water has been moving through the masonry.
Where the salt comes from
Salts are present in the materials themselves — in cement, in clay bricks, in sand, and in groundwater. They are inert while dry. Water moving through the wall dissolves them, carries them to the surface, and evaporates, leaving the salt behind as crystals.
So efflorescence always means the same thing: **water has moved through this wall and evaporated at this point.**
New build versus persistent
**New construction efflorescence** is common and usually self-limiting. A new wall holds a lot of construction water, and as it dries over the first year or two the soluble salts come out. It reduces each season and stops.
**Persistent efflorescence** on an older building is different. It means water is still getting in. Something is wrong: a failed flashing, a leaking gutter, ground levels above the damp course, a cracked sill, a plumbing leak, or rising damp.
The distinction matters entirely. The first needs patience. The second needs investigation.
Efflorescence and cryptoflorescence
Salt crystallising **on** the surface is efflorescence — unsightly, essentially harmless.
Salt crystallising **within** the material, just below the surface, is cryptoflorescence, and it is destructive. Crystal growth in the pores exerts pressure that spalls the face off brick and blows render off the wall.
The second is what happens when you seal a wall that is still carrying moisture. The salts can no longer reach the surface, so they crystallise behind the coating instead — which is precisely why sealing a damp wall makes the damage worse rather than better.
Do not paint over active efflorescence
The coating will fail, and the salts will do more damage trapped than they were doing exposed. Efflorescence must have stopped before a wall is coated.
Removing it
**Brush it off dry.** A stiff bristle brush — not wire, which leaves steel particles that rust and stain. Do this on a dry day and collect what falls.
**Do not start with water.** Washing dissolves the salt and drives most of it back into the wall, where it will re-emerge. You get a clean wall for a fortnight and the same problem after.
**Rinse only after brushing**, with minimal water, and let the wall dry thoroughly.
**For stubborn deposits**, proprietary efflorescence removers based on dilute acids are available. Follow the instructions exactly, wet the wall first to prevent the acid being drawn in, and neutralise afterwards. Acid on the wrong substrate — particularly limestone — causes damage of its own.
The part that actually matters
Removing efflorescence treats the symptom. Unless the water source is found, it returns.
Walk the wall and look for:
- Gutters overflowing or leaking at joints
- Downpipes discharging against the wall base
- Garden beds or paving above the damp course
- Cracked or missing sill flashings
- Failed pointing in the mortar joints
- Irrigation spraying directly onto masonry
- A plumbing leak inside the wall
That last one is worth ruling out early if the efflorescence is in an unusual position with no obvious external cause.
When you can finally paint
Once the source is fixed, the wall has dried, and no new deposits have appeared through a full wet season. Then use a **permeable** system, so any residual moisture can still leave the wall rather than accumulating behind the film.