Damp, mould and structural
Efflorescence: the white bloom on bricks and walls explained
Efflorescence is a white, powdery or crystalline bloom that appears on brick, render and plaster when moisture carries natural salts to the surface and evaporates, leaving the salts behind. It is common on new brickwork, usually harmless, and brushes off easily. Recurring efflorescence, though, can be a sign of a persistent damp source.
- Also known as
- salt bloom, wall salts, whiskering
- Easily confused with
- mould (which is dark, not white), lime bloom, paint or render failure
- How serious
- Low: harmless in itself, but recurring salts can flag a damp source
- Typical cost
- Usually no cost for DIY control
How to identify efflorescence
Efflorescence looks like a fluffy or crystalline white deposit on the surface of brick, mortar, render or plaster. It is dry to the touch and brushes off as a powder, unlike mould, which is dark and often furry or slimy.
It is very common on newly built or recently wetted brickwork as the natural salts in the materials migrate out while they dry, and it often appears after wet weather or where a wall has been damp.
How serious is it?
Low: harmless in itself, but recurring salts can flag a damp source
Efflorescence itself is cosmetic and harmless. On new brickwork it usually fades over the first year or two as the soluble salts are used up.
It matters as an indicator. Efflorescence that keeps returning, or appears indoors on plaster, tells you moisture is repeatedly moving through the wall, so the useful response is to find and fix that damp source rather than just wiping off the salts.
How to fix it yourself
- Brush the dry salts off with a stiff, dry brush. Do this dry first, because wetting the deposit can redissolve the salts and draw more to the surface.
- For stubborn deposits on external brick, a specialist efflorescence remover can be used following the product instructions, then rinse and allow to dry.
- Do not seal a wall to hide it before the moisture is understood, as trapping salts and water can cause further damage.
- If it keeps coming back, look for the moisture feeding it: a leak, penetrating damp, or a new wall still drying out.
When to call a professional
- Efflorescence keeps returning after removal, especially indoors, which suggests a continuing damp problem rather than initial drying.
- It appears alongside other damp signs such as a tide mark, peeling plaster or persistent mould.
Who to call
- A damp surveyor or Property Care Association member to identify the moisture source if salts keep recurring.
- A builder for repointing or render repair where the wall fabric is letting water in.
Frequently asked questions
Is efflorescence a sign of damp?
A one-off bloom on new brickwork is just normal drying and is harmless. But efflorescence that keeps returning, or appears indoors, means moisture is repeatedly travelling through the wall, so recurring salts are a useful warning to find and fix a damp source.
How do I get rid of efflorescence?
Brush the dry salts off with a stiff brush first, since wetting them can draw more to the surface. For stubborn external deposits, a proprietary efflorescence remover can help. If it keeps returning, address the underlying moisture rather than repeatedly cleaning the surface.
Is efflorescence the same as mould?
No. Efflorescence is a white, dry, powdery salt deposit that brushes off, while mould is dark, often furry or slimy, and is a living fungus linked to damp and condensation. They look different and need different responses, so identify which you have before treating it.
Sources
Editor, HomesAndHedge
Oliver leads HomesAndHedge's editorial coverage of home and garden problems. He researches and writes the plain-English explainers on pests, invasive plants, damp and mould, drainage and wildlife, drawing on guidance from bodies such as the Property Care Association, the RHS and the NHS, and is clear about when a job needs a qualified professional.
Last reviewed: 8 June 2026