White powder or crystals forming on walls
The white deposit is efflorescence — salts carried out of the masonry by moving water and left behind as it evaporates. It is not the problem itself. It is proof that water is moving through the wall, and it tells you where it is leaving.
Stable enough to schedule properly. Best resolved before the next monsoon rather than during it.
Probable causes, ranked
Ordered by how often we find each one to be the actual source. The 'tell' is what distinguishes it from the others.
- 01most common
Persistent water movement through the masonry
The tell — Deposits return within weeks of being brushed off.
External Plaster & Painting → - 02common
Impermeable paint applied over a damp wall, trapping salts behind it
The tell — Paint blisters outward with crystalline deposits behind the blister.
Silane-Siloxane Water Repellent Treatment → - 03common
Rising damp drawing ground salts up the wall
The tell — Deposits concentrate near the plinth with a horizontal tide line.
Chemical Coating → - 04less common
New construction drying out
The tell — Occurs once on a recently built wall and does not return after cleaning.
Cement Based Coating →
Sixty seconds, before you call anyone
- Photograph it while it is actively wet. A dried stain tells a surveyor far less than a running one.
- Note whether it worsens with rain or with usage. Rain-linked points to the building envelope; usage-linked points to plumbing. This single distinction settles most arguments about responsibility.
- Check the area directly above and beside the damage, not only below it. Water travels along a slab before it drops.
- Look specifically for the tell of the most likely cause: deposits return within weeks of being brushed off.
- Do not chip into saturated plaster or paint over a damp patch. The first risks bringing material down; the second destroys the evidence needed to trace the path.
What it becomes if you leave it
Salt crystallisation exerts real pressure inside the pores of the plaster and masonry. Over time it breaks the surface apart from within — which is why repainting over efflorescence fails every season until the water path is closed.
Often seen alongside this
- Damp patch spreading on an internal wall
A damp patch on an internal wall means water is reaching the wall from somewhere you cannot see — usually the external face, a concealed pipe, or the slab above.
- Paint peeling or blistering after the monsoon
Paint fails after the monsoon because it was applied over a substrate that was damp, hollow or unprimed.
- Plaster falling off an external wall
Plaster falling from a facade is a safety issue before it is a building one — falling material from height injures people.
White powder or crystals forming on walls — questions we get asked
What is the most likely cause of white powder or crystals forming on walls?
Persistent water movement through the masonry. The sign that points to it is: deposits return within weeks of being brushed off. That said, the ranking here is a starting point — the actual source is confirmed by survey, because more than one of these can be true at once.
What happens if I leave it?
Salt crystallisation exerts real pressure inside the pores of the plaster and masonry. Over time it breaks the surface apart from within — which is why repainting over efflorescence fails every season until the water path is closed.
Can I diagnose this myself before calling anyone?
Partly, and it is worth doing. Photograph it while it is actively wet, note whether it worsens with rain or with usage, and check the area directly above and beside the damage. That single rain-versus-usage distinction narrows the cause more than anything else you can do in sixty seconds.
How urgent is this?
Plan it. Stable enough to schedule properly. Best resolved before the next monsoon rather than during it.
Send us a photograph and we will tell you what we think it is
WhatsApp a photo taken while it is wet, with a note on whether it tracks with rain or with usage. That is usually enough for a first opinion, and the site inspection that follows is free.
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