Salt damp is the kind of damp that wastes the most money on paint. You paint, it holds for a few months, it bulges and sheds white powder again, and you paint again. Each cycle is worse because the wall builds up more salt. This guide explains what the salts are, where the water comes from, why the paint falls off and how to treat it so the next coat lasts.
What the salts are
The technical name is efflorescence. They are mineral salts (sulphates, nitrates, chlorides) that were dissolved in the water moving through the wall. When that water reaches the surface and evaporates, the salt stays behind and crystallises. You see it as white powder, small crystals, a crust or paint lifted in blisters. Sometimes the render crumbles when touched.
The salts may come from the material itself (mortar, brick, block) or from the water carrying them: from the ground, from the sea, from fertiliser in a garden next to the facade. Either way, salt deposits are proof that liquid water is moving inside the wall. It is not condensation.
Where the water comes from
- Rising damp. The most common case. The wall absorbs water from the ground and draws it up through its pores, just like a sugar lump. It reaches between 30 cm and 1.5 m in height depending on the material and the amount of water. It affects ground floors, basements, garages and houses with no damp-proof course at the base of the wall (almost all those built before the 1980s and many self-built homes).
- Lateral ingress. Walls in contact with the ground on one side (terraced plots, raised gardens, basements). The water comes in from the side, not from below. It is treated as water ingress.
- Marine environment. On the first and second line of the coast, the air carries chlorides that settle on facades and enter with the moisture. Combined with rising damp, it is the worst scenario: very common on the Canary Islands coast.
- Salts from the material itself. A new render can release efflorescence during the first few months while it cures. It usually disappears by itself; if not, it is treated the same way.
NeutralySalt Primer
Anti-salt treatment: it helps prevent salts (salt deposits) from crystallising on the surface. It lets the wall breathe.1 L and 5 L · 25–30 m²/L
Why the paint falls off
When salt crystallises, it takes up more volume than when dissolved. That expansion creates pressure from the inside out. A conventional emulsion forms a closed film: the salt pushes from behind, the film comes away and blisters form that end up bursting. The film also blocks evaporation, so the water climbs higher looking for a way out and the stain grows.
A breathable paint holds up better because it lets water vapour out of the surface instead of trapping it. But if the salts are not treated, crystallisation at the surface ends up staining and breaking down that coat too. That is why salts need two steps, not one.
How to tell it apart from condensation
| Salts / rising damp | Condensation |
|---|---|
| Low, horizontal band, starting from the floor | Upper corners, ceilings |
| White powder, crust, bulging paint | Black or greenish spots |
| Render that crumbles | Render intact |
| Worse in rainy periods or with saturated ground | Worse with cold and closed windows |
| Ground floor, basement, garage | Any floor, north-facing walls |
They can occur on the same wall: a band of salts at the bottom and mould at the top. If it isn't clear, the guide how to tell what kind of damp you have sorts it out in five minutes, or send photos for a free diagnosis.
Treatment step by step
- Scrape it dry. With a scraper and a stiff-bristled brush, remove loose paint, crusts and all the render that sounds hollow when you knock on it with your knuckles. Go back to a sound surface even if the area gets bigger. Collect the dust with a vacuum cleaner, not with water.
- Don't wash with water. Water dissolves the salt and carries it back into the wall. It is the most common mistake and the one that explains why many treatments fail within weeks.
- Repair. Fill the gaps with repair mortar. If you can choose, lime mortar or a mortar specifically for damp surfaces: gypsum plaster is the worst material in an area with salts. Leave to cure for as long as the manufacturer states, which for thicknesses of more than one centimetre can be a week or more.
- Apply NeutralySalt Primer. It is an anti-salt treatment for mineral walls which, according to its technical data sheet, stops the migration and crystallisation of soluble salts without affecting the breathability of the surface. One litre covers between 25 and 30 m², so for an affected band of wall, one tin covers the damaged area and a margin of 30–40 cm above it, which is where the water will carry on evaporating. It is applied neat, undiluted, by brush, roller or sprayer, in 1–2 coats wet on wet and without rinsing. Wait at least 24 h before the finish.
- Paint with MATE5000. Two coats of breathable paint with a deep matt finish, which lets water vapour out of the surface instead of trapping it. A 4 L tin covers around 10–14 m² in two coats (5–7 m²/L per coat) and costs 19,02 €. If you are going to paint the whole wall, work out the quantity with the calculator.
What you are aiming for with this treatment is to help prevent salts crystallising at the surface and to have a finish that doesn't trap water. What you don't achieve is stopping the water: if the source is still active, the wall will still have damp at the base and it is worth keeping an eye on it.
When building work is needed
There are clear signs that surface treatment alone is not enough:
- The damp band rises more than 50 cm and grows every winter.
- A moisture meter shows high readings in the wall several days after the last rain.
- The wall is stone or block and is in direct contact with the ground with no barrier or drainage of any kind.
- The ground-floor floor is also damp or the flooring is lifting.
- There is a garden, a terraced plot or a water tank right against that facade.
The building solutions for rising damp are a chemical injection barrier (the wall is drilled at the base and a water-repellent product is injected to stop the rise), perimeter drainage if the water comes from adjoining ground, and a ventilated plinth or macroporous render so the wall can evaporate without damaging the finish. These are jobs for a builder or a specialist company, and their price depends a great deal on the thickness and material of the wall. The electro-osmosis systems sold as "no building work" give very uneven results; be wary of guarantees of complete drying.
After any of that work, the wall is still loaded with salt. Treatment with NeutralySalt Primer and MATE5000 is the right finish for the paint to last once the water has been stopped.
Maintenance
Check the area every autumn. If a little white powder appears at the joint with the floor, brush it off dry and do nothing more. If the paint bulges again in less than a year, water is coming in with more force than the surface can handle and it is time to think about building work. The full process is on the salts and rising damp page. The two products in the treatment are NeutralySalt Primer and MATE5000; there is no set kit for salts because every wall is different, so send us a photo and we'll tell you what yours needs.
Guía escrita y revisada por el Equipo Humix Paint con los datos de las fichas técnicas de cada producto. La pintura actúa en la superficie: si el agua sube del suelo o entra de fuera, primero se trata la causa.
