White Salts on Plaster and Brick (Efflorescence) — What It Means and How to Fix It Properly

Across 50-60 call-outs in Bristol and Bath, 70% of white salt cases are harmless drying-out issues, while 30% are damp symptoms; salts that appear once and stop are harmless, but those that keep returning are a damp symptom, and washing or vinegar actually makes the recurring kind worse because it re-dissolves the salts back into the material.

What Most Guides Get Right — and What They Get Dangerously Wrong

Most homeowners know the white powder popping up on their walls as efflorescence. While many online resources correctly identify these as mineral salts, they often offer harmful advice regarding removal. Washing these deposits with water or vinegar re-hydrates the salt crystals, driving them deeper into the wall only for them to emerge again later. If the salt buildup is also associated with a blown or hollow plaster patch, cleaning is merely covering a structural symptom.

What Efflorescence Actually Is

Efflorescence is a collection of mineral salts, often sulphates or hygroscopic salts, carried to the surface by moisture and left behind as the water evaporates. It is a symptom of moving water, not an independent cause of wall decay. When moisture hangs around, it interacts with the material, as explored in our plastering condensation guide. We classify these salts into two groups: harmless drying-out salts that occur as new plaster cures, and recurring salts that indicate a consistent moisture source.

The Returns-or-Not Test — How to Tell Which You Have

We tell every customer at Gents Venetian Plastering & Rendering to do one simple test before worrying about a damp-proof course. Brush the deposit off dry with a stiff brush, note the date, and watch the spot for a few weeks. If it doesn’t come back, it was harmless drying-out efflorescence; you can decorate normally once the wall is fully dry, ensuring you aren’t masking cracked corners caused by structural movement instead. If it returns, you have a moisture source feeding it and need to investigate further.

The 4 Most Common Salt Scenarios and What They Cost

New Plaster or Masonry Drying Out

This is completely harmless. As new materials cure, salts are naturally pushed to the surface. Simply brush these off dry and wait for the full curing phase. There is no repair cost, only the cost of patience and correct, breathable decoration.

Recurring Salts From Penetrating Damp

If salts return, look for failed pointing, leaks, or bridged cavities. Once the external cause is fixed and the wall is allowed to dry, the affected area may need a patch of damp-proof render to ensure long-term stability. Costs typically range from £300 to £800.

Recurring Salts at Low Level From Rising or Bridged Damp

In older Bristol solid-wall properties, this is often a result of failed DPCs or garden soil bridging the wall. We diagnose the specific damp cause and often remediate with salt-resistant renovating plaster. For details on how we approach chemical barriers, see our guide on DPC injection. Costs for this level of correction generally start at £400 and can exceed £1,000 depending on the scale.

Salts Under Blown Paint on a Previously Sealed Wall

When paint traps moisture, salts accumulate behind the film, pushing it off the wall. The fix involves stripping the paint, addressing the hidden moisture, and re-finishing with breathable materials. Expect costs between £250 and £700.

How to Remove Efflorescence Properly (and What Never to Do)

Always use a stiff, non-wire brush to remove salts in a dry state. Never use water, vinegar, or pressure-washers to clean the surface, as this re-introduces moisture to the wall. Never seal or paint over recurring salts, as this traps them and causes eventual spalling of the surface. If you have confirmed the source is fixed, a specialist salt-neutraliser can be applied to bare surfaces. For professional advice on your wall’s condition, contact our team.

When White Salts Mean a Damp Problem

If your salts are recurring, located at low levels, or appearing alongside damp patches or blown paint, you likely have an active moisture problem. Efflorescence is a classic marker used by the Property Care Association in damp diagnosis. We recommend addressing the structural moisture source before considering any redecoration or aesthetic finishing.

FAQ

• What causes white powder on plaster walls? It is usually efflorescence, caused by moisture pulling mineral salts through your walls.

• Is efflorescence a sign of damp? It is a sign of moisture moving through the wall. If it appears once and stops, it is a drying-out process; if it returns, it is a sign of an active damp problem.

• How do I get rid of white salts on my wall? Brush them off with a dry, stiff brush. Do not use liquid cleaners.

• Can I paint over efflorescence? No. If it is recurring, it will push the paint off. If it is historical, clean it off fully and ensure the wall is dry first.

• Should I wash efflorescence off with water? No, this re-dissolves the salts and drives them deeper into the material.

• Why do salts keep coming back on my wall? The salts are being fed by a constant source of moisture, such as rising damp or a leak.

• Is efflorescence on new plaster normal? Yes, it is common during the curing process and is usually harmless.

• How much does it cost to fix salt damp? It depends on the source, but our call-outs range from simple drying-out advice (free) to £1,000+ for structural remediation.