Why salts appear on your walls
What those white deposits pushing off paint and plaster are, what they tell you, and why scraping them off and repainting is not enough.
Salts are the white, sometimes powdery or fluffy deposits that appear low down on some walls. They are not dirt or mould: they are minerals.
Where they come from
Groundwater contains dissolved salts. When it rises through a wall and evaporates at the surface, the salts are left behind as crystals.
That makes salts one of the clearest signs of rising damp: they show that water is moving through the wall and evaporating at the surface.
Why they push off paint and plaster
As salts crystallise, they expand. When that happens just under the paint or inside the plaster, it is forced outwards, causing bubbling, flaking and plaster that crumbles to the touch.
Some of these salts are also hygroscopic: they draw moisture from the air. That is why salty plaster can stay damp, and give high meter readings, even once the wall behind it has started to dry.
Why they keep coming back
Scraping the salts off and repainting only removes what you can see. While the wall keeps drawing water from the ground, new salts will reach the surface, usually within a few months.
Even once the damp is under control, salts already in the wall can keep appearing for a while as it dries out. That is normal and worth bearing in mind before redecorating.
What to do
- Confirm the cause with readings at different heights on the wall.
- Deal with the cause, not just the marks.
- Let the wall dry before replastering and redecorating, ideally with breathable materials such as lime-based plaster or a salt-resistant render.
At a free BiXos assessment we take readings from the wall and explain what is going on before recommending anything.