What the pattern tells you
| Where the salts appear | What it usually means |
|---|---|
| A level band 0.9–1.2m up an internal wall | Rising damp — the evaporation line |
| Scattered patches on external brickwork | New-build salts washing out; usually settles |
| Broad band matching the soil level outside | Lateral damp from retained earth |
| Around a single crack or joint | Penetrating damp through that defect |
| On a basement or retaining wall | Hydrostatic pressure from the negative side |
| Under a window or below a sill | Failed sill detail or blocked drip groove |
Why efflorescence keeps coming back after you clean it
Because cleaning removes the deposit, not the salt. Most of the salt is still inside the plaster, and it is hygroscopic — it pulls moisture out of humid air on its own account, which is why a salt-contaminated wall can look damp even in dry weather, even after the original water source is dealt with.
This is the reason a chemical DPC on its own is only half a treatment. If the contaminated plaster stays on the wall, it goes on drawing moisture from the room air indefinitely and the owner concludes the injection failed. Hacking it off to at least 300mm above the highest tide mark and re-rendering with a salt-inhibiting mix is not an upsell — it is the part that makes the rest work.
The full sequence is on damp proofing in Cape Town.
What not to do
- Do not wash it with water. You dissolve the salts and drive them back into the wall, and they return as soon as it dries.
- Do not paint over it. Nothing bonds reliably to a salt-bearing surface. The paint lifts, usually within a season, and takes some plaster with it.
- Do not seal the wall. A film-forming coating traps the moisture and moves the failure plane behind the plaster instead of in front of it.
- Do brush it off dry if you just want it gone cosmetically, and accept it will return until the water is dealt with.
Related reading
Start with The Four Types of Damp for the overview, or:
- Paint Peeling Off Walls
- Musty Smell in the House
- What a Damp Survey Should Actually Cover
- Water Ingress Explained
Common questions
Is efflorescence dangerous?
The deposit is not harmful in itself. It matters because it is evidence of moisture moving through the wall, and because salt crystallising inside the masonry rather than on it (called crypto-efflorescence) can spall brick faces and blow plaster over time.
Will efflorescence go away on its own?
On new brickwork, usually — construction salts wash out over the first year or two. On an older wall that has started producing salts where it did not before, no. Something has changed in how water is moving through that wall.
How do I remove efflorescence?
Brush it off dry with a stiff brush, never wet. Specialist acidic cleaners exist but they attack mortar and only address the surface. Neither approach touches the cause, which is the reason it appeared.