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Salt Deposits On Walls
A white or grey bloom, fluffy crystals or a hard crust is coming through the plaster or the brickwork.
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What's happening?
Salts are evidence, not a disease. Masonry and groundwater both contain soluble salts, and when water moves through a wall it carries them along and leaves them behind at the surface where it evaporates. The white fluffy bloom you can brush off is efflorescence, sitting on the face. The harder crust that forces plaster and paint off from behind is crypto-florescence, crystallising within the material and expanding as it does. Two salt families matter most in a diagnosis: nitrates and chlorides, which are hygroscopic — they attract water out of the air, so a salt-contaminated wall stays damp to the touch and reads high on a meter even after the original source of water has been cured. That property is exactly why salts confuse damp surveys.
What usually causes it?
- Rising damp bringing ground salts up into the plaster over a long period
- Penetrating damp or a plumbing leak washing salts out of the masonry to the surface
- Salts native to new brickwork or mortar, drying out after construction
- Chimney breasts contaminated with hygroscopic salts from decades of combustion products
- A previously cured damp problem leaving salt-laden plaster that stays damp on its own
- Gypsum plaster applied directly onto damp masonry, which then carries the salts through
- De-icing salt or fertiliser splashing onto the base of an external wall
Is it dangerous?
The salts themselves are not a health hazard. What they do is keep destroying finishes and keep misleading diagnoses. Plaster contaminated with hygroscopic salts will never feel dry, will keep blowing paint and wallpaper off, and will read damp on a conductivity meter indefinitely — which is how homes end up with repeated damp treatments to a wall whose original water source was fixed years ago.
Can I fix it myself?
Brushing off surface efflorescence dry is fine, and worth repeating as it reappears while the wall dries. Two things not to do. Do not wash it off with water — that dissolves the salts and drives them back into the wall to come out again. And do not paint or paper over it: contaminated plaster keeps the moisture and pushes the finish straight back off. Whether the plaster has to come off at all is the question that needs the diagnosis first.
When should you call a damp proofer?
Call a damp proofer to find what carried the salts there, since salts are always a symptom. It is worth being specific about timing — salts that appeared after a leak was fixed, or after a damp course was installed, usually mean the plaster is now the problem rather than the wall. Call before redecorating, because replastering a salted wall in the wrong specification simply repeats the failure.
What will the damp proofer actually do?
- Identify the salt type where it matters, distinguishing hygroscopic nitrates and chlorides from construction salts
- Trace and cure the water movement that transported them — leak, rising damp, penetrating damp or bridging
- Measure moisture and salt content in the masonry to separate genuine dampness from hygroscopic behaviour
- Remove contaminated plaster back to sound material where it has become the moisture reservoir
- Replaster to a specification that resists salt migration, with the correct render coats and mix
- Give a realistic drying period before decoration, and say what readings to expect during it
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