📌 In short
Paint and plaster blister and fall off because they are being pushed off by moisture and salt coming from inside the wall. As water evaporates inside the wall, the salts it carries crystallise; as the crystals grow, they push the paint and plaster outwards from within. That is why repainting or replastering the area does not solve anything — it blisters again in the same spot within a few months. The permanent fix: first stop the source of the damp (DampStop), then renew the surface with a salt-resistant, breathable plaster (HydroFix).
Why Do Paint and Plaster Blister?
Blistering paint is usually blamed on bad paint or bad workmanship. Yet if it keeps blistering in the same place, the culprit is not the paint — it is the wall itself. Here is what happens:
- There is moisture inside the wall (usually water rising from the ground).
- As the water travels towards the surface, it carries along the salts it picks up from the soil and the mortar.
- When the water evaporates just below the surface, the salts stay behind and crystallise.
- As the salt crystals grow they expand in volume, pushing the paint — and even the plaster — outwards from within.
So blistering paint is in fact the first visible sign of a damp problem quietly progressing inside the wall. Crumbling plaster is the advanced stage of the same process: over the years, salt and moisture dissolve the bonds that hold the plaster to the wall.
Why Does It Come Back After Every Repaint?
Because painting covers the result of the problem but changes nothing about its cause. As long as water keeps entering the wall, the salt transport continues too; the new paint shares the same fate within a few months. What is more, every extra layer breathes a little less, so the moisture climbs higher inside the wall — in many of our customers' homes we see the blistering zone creep a little higher after each repaint.
For the same reason, "waterproof" paints and coatings backfire on a damp wall: they trap the moisture, the pressure builds, and the coating blows off from behind. We look at this in detail in can paint fix a damp problem?
Does This Sound Familiar? Quick Checklist
If two or more of the following apply, the problem is not the paint — it is the damp in the wall:
- The blistering keeps recurring in the same area, usually on the lower part of the wall
- White powder or sand-like grains fall out of the blisters
- The plaster has debonded at skirting level and sounds hollow when tapped
- There is a damp line or map-patterned staining along the base of the wall
- The problem becomes more pronounced in winter
If you can also see a horizontal damp mark around the blistering, have a look at the damp line on walls page; if white powdery deposits stand out, see the salt efflorescence page — the three are very often different faces of the same problem.
The Permanent Fix: Stop the Damp First, Then Renew the Surface
The order matters enormously; any repair that starts from the wrong end is wasted effort:
- Stop the source of the damp: If the blistering is caused by rising damp, DampStop injection is applied along the bottom course of the wall; a permanent water-repellent barrier forms in the pores.
- Remove the damaged plaster: The blistered, salt-laden plaster is chipped away back to sound substrate (together with roughly 50 cm around the damaged area).
- Apply breathable plaster: The surface is renewed with HydroFix damp-proofing plaster. HydroFix releases the remaining moisture in the wall without trapping it and is resistant to salt damage — the blistering cycle ends here.
- Choose the right paint: A breathable (diffusion-open) paint is used as the final coat; waterproof layers are avoided.
If you would like to carry out the whole application yourself, the DampStop Complete Kit brings the necessary materials and equipment together in a single box, and the step-by-step application guide walks you through the process.
Products Used to Solve This Problem
HydroFix 10 kg Damp-Proofing Plaster
Applied to the surface after the damp-proof barrier; a breathable, salt-resistant repair plaster.
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DampStop 5L Injection
Injected into holes drilled along the bottom course of the wall; forms a silicone barrier that stops the water from rising.
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DampStop Complete Kit
DampStop + HydroFix + application equipment. A complete solution in a single box.
View ProductSee how the three products work together: The Triple System →
Frequently Asked Questions
Isn't it enough to scrape off the blistered area and repaint?
No. The cause of the blistering is not the quality of the paint but the moisture and salt coming from inside the wall. Any paint or plaster repair carried out without stopping the source is temporary; the same area usually blisters again within a few months. First the damp must be stopped, then the surface renewed.
Can gypsum plaster be applied to a wall where the plaster is crumbling?
On a damp wall, gypsum is the least durable option; it absorbs water, softens and starts shedding again in no time. Walls that have suffered damp problems need special breathable, salt-resistant repair plasters (e.g. HydroFix).
Will water-repellent (waterproof) paint solve it?
On the contrary — it can make things worse. A waterproof layer traps the moisture in the wall; unable to escape at the surface, the water climbs higher and the pressure blows the layer off from behind. On a damp wall the aim is not to trap the moisture but to stop the source and let the wall breathe.
How do I know the damp has been stopped, and when can I renew the surface?
After the injection, the existing moisture inside the wall decreases by evaporating from the surface; the base of the wall dries out and the smell disappears. Because HydroFix is a breathable plaster, surface renewal can begin immediately after the barrier has been applied; the remaining moisture escapes by evaporating through the plaster.
Learn More: Related Guides
- Can Paint Fix a Damp Problem?
- HydroFix Damp-Proofing Plaster vs Normal Plaster: What Is the Difference?
- How Can I Tell If the Damp on My Wall Is Rising Damp?
Not sure? Send us a photo and we will tell you
Send photos of the problem area; our technical team will assess the cause within 24 hours and recommend a solution tailored to you. Free of charge, with no obligation to buy.
