White salt marks and damp at the bottom of the wall?
A damp band at the bottom of the wall with white, salty powder (efflorescence) usually means moisture is rising through the masonry from the ground or the floor. The water evaporates at the surface and leaves salt behind, which pushes off paint and crumbles plaster. Mopping water entering at the skirting can look similar, and its fix is much simpler.
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Signs you will notice
- White, fluffy or crystalline powder on the wall surface
- Damp band from the floor up to about knee height
- Plaster crumbling or sounding hollow near the floor
- Paint and putty bubbling just above the skirting
- Most common on ground floors and walls touching soil
Where the water usually comes from
Often more than one source is at work, and each needs its own fix.
Cause 1
Damp rising from the floor, with white salt marks
Damp and salt rising from floor level on an inside wall, with plaster crumbling.
Check it yourself: Press the plaster near the floor. Soft, powdery or hollow plaster means the damp has been there for a long time.
How it is usually fixed: Remove the damaged plaster down to the masonry, apply a flexible waterproof barrier and replaster with a waterproof, polymer-modified mix.
Cause 2
Damp rising at the base of an outside wall
The same signs at the base of an outside wall, often at plinth level.
Check it yourself: Look at the outside base of the wall. Is the ground or paving higher than the inside floor, or sloping towards the wall?
How it is usually fixed: Remove the plaster at plinth level, apply a flexible waterproof barrier on the masonry and replaster with a polymer-modified mix.
Cause 3
Mopping water getting in at the skirting
A narrower band just above the skirting, in rooms that are wet-mopped, and little salt.
Check it yourself: Check the joint between skirting and floor tiles for gaps, and whether the floor is washed with a lot of water.
How it is usually fixed: Seal the skirting-floor joint and any open floor tile joints with epoxy grout, and use less standing water when cleaning.
Methods follow proven, manufacturer-approved waterproofing systems. The right one for your building depends on what is found on site.
What a photo can and cannot tell you
Photo guidance points to the likely source. It is not a confirmed diagnosis.
A clear photo can show
- The height and pattern of the damp band
- White salt deposits and the state of the plaster
- Gaps at the skirting
A photo cannot settle
- Whether the wall has a damp-proof course
- The ground level outside compared with the floor inside
- How much moisture is inside the masonry
Simple checks before you call anyone
- 1Note the height of the damp band and whether it is the same along the whole wall.
- 2Check if the room is on the ground floor or the wall touches soil outside.
- 3Look for gaps between skirting and floor tiles.
- 4Brush off the white powder and see whether it returns within days.
When you need someone on site
- Plaster has to come off over a large area
- The damp rises higher than about a metre, which suggests another source
- The wall also shows structural cracks
Where Membrain works on site, a site diagnosis confirms the source, and thermal imaging finds hidden leaks before anything is broken. The app checks whether your pincode is covered.
Common mistakes that waste money
- Scraping off the salt and repainting. It returns within weeks.
- Using ordinary cement plaster again on a wall still drawing moisture.
- Sealing the wall with oil paint, which traps moisture and makes it worse.
- Ignoring the outside ground level and drainage.
Before you accept a contractor's quote
- Does it remove the damaged plaster down to the masonry?
- Does it apply a waterproof barrier before replastering?
- Does the new plaster use a polymer-modified or waterproof mix?
- Does it address outside ground level or drainage where relevant?
Already have quotes? Membrain can compare them on scope, not just price. Planning the work instead? A written specification makes quotes comparable.
How this guide is built
Diagnostic basis
Membrain separates visible signs from possible water-entry mechanisms, then asks for evidence that can distinguish the remaining causes.
Repair-source governance
Public guides stay brand-neutral. When Membrain creates a repair plan, methods and products come from current approved manufacturer documents in its technical library.
Evidence limits
A photo cannot confirm concealed pipes, waterproofing layers or moisture depth. When remote evidence cannot separate the causes, a site inspection is the correct next step.
Technical notes behind this guide
Deeper reasoning on the moisture patterns and water-entry mechanisms used to interpret this problem.
Deewar pe safed namak aur neeche se seelan kyun?
Deewar ke neeche ke hisse mein seelan ke saath safed powder dikhe, toh nami zameen ya farsh se upar chadh rahi hai. Paani sookhta hai aur namak chhod jaata hai, jo paint aur plaster ko kharab kar deta hai.
Sirf ghis ke paint karne se kuch nahi hoga. Kharab plaster hata ke waterproof layer lagana padta hai. Pehle check karo ki kahin ye pochhe ka paani toh nahi, uska ilaaj bahut aasaan hai.
Frequently asked questions
What is the white powder on my wall?
Usually salts carried by moisture moving through the wall. When the water evaporates, the salts stay on the surface. It is a sign of ongoing moisture.
Can I just scrape and repaint?
The salt and damp will return because the moisture is still moving through the wall. The damaged plaster has to be removed and a barrier applied.
How is rising damp different from a pipe leak?
Rising damp forms a fairly even band along the wall base. A pipe leak is usually concentrated around one point or along a pipe route and does not change with the seasons.
How high should the plaster be removed?
Usually some distance above the highest visible damp, so the barrier covers the full affected zone. A contractor should mark it on site.
Not sure which one it is?
Share a photo and answer a few questions. Membrain shows the likely sources and a repair plan built from proven waterproofing methods, in minutes. Free to start.
Remote guidance, not a site inspection.