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Why Is My Plaster Bubbling? Causes and How to Fix It
Updated 3 November 2026. Reviewed by Michael Young, Head Contractor at Advanced Damp (CSSW and FODCS).
Key Takeaways
- Bubbling plaster is almost always caused by moisture or salts behind the surface, not by the plaster itself.
- The most common causes are rising damp, penetrating damp, leaks, condensation and salt contamination from past damp.
- Filling and repainting will not last if the moisture source is still there. The cause has to be fixed first.
- Salt contaminated plaster usually needs removing and replacing with a salt resistant system.
Bubbling or blistering plaster is one of the clearest signs that something is wrong inside a wall. The surface lifts into raised patches, paint peels or flakes, and the plaster underneath can feel soft, powdery or hollow when you press it. It is easy to treat it as a decorating problem, but in most cases the bubbles are the visible end of a moisture problem. This guide explains what causes plaster to bubble, how to work out which cause you have, and how to repair it properly.
What Does Bubbling Plaster Look Like?
- Raised blisters or bubbles in paint or plaster, sometimes filled with air or a white powder
- Paint peeling or flaking away in sheets
- White, fluffy or crystalline deposits on the surface
- Plaster that sounds hollow when tapped, or crumbles when pressed
- Tide marks, staining or discolouration nearby
- A musty smell in the room
Where the bubbles appear is one of the best clues to the cause, so note whether they sit at low level, high on the wall, around a window or chimney, or across a whole wall.
What Causes Plaster to Bubble?
Rising Damp
Moisture drawn up from the ground into a wall with no working damp proof course carries salts with it. As the water evaporates from the plaster, the salts crystallise and push the paint and plaster off the wall. Bubbling from rising damp typically sits within roughly a metre of the floor, often with a tide mark above it. Our guide to the signs of rising damp covers the other symptoms.
Penetrating Damp
Water getting in from outside through defective pointing, cracked render, failed gutters, leaking flashings or a damaged sill can saturate the wall at any height. Bubbling from penetrating damp usually lines up with a defect on the outside face of the wall, and often gets worse after heavy rain. See our guide to penetrating damp.
Leaks
Leaking pipes, radiators, showers and bathroom seals can soak plaster quickly. The bubbling tends to be localised around the source, and can appear suddenly.
Condensation
Moist air settling on cold walls can lift paint, especially in bathrooms, kitchens and bedrooms. Condensation usually comes with mould, streaming windows and black spotting in corners rather than salt deposits. Our article on treating condensation on walls explains how to tell.
Salt Contamination
Walls that have been damp in the past can stay loaded with salts long after the moisture source is fixed. Some of these salts draw moisture from the air, so the plaster keeps blistering on humid days. This is why plaster can carry on bubbling after a damp proof course has been installed if the old plaster was not replaced. The same process causes efflorescence on brickwork.
Poor Preparation or the Wrong Materials
Less often, bubbling is caused by painting over plaster that had not dried out, by poor adhesion between coats, or by using impermeable paints and gypsum plaster on solid walls that need to breathe. These faults usually appear soon after the work was done.
How to Find the Cause
- Check the height and pattern. Low level bubbling with a tide mark points to rising damp. Patches lining up with an external defect point to penetrating damp.
- Look outside. Check ground levels, gutters, downpipes, pointing and render on the other side of the wall.
- Check for leaks. Look for pipes, radiators, showers or a bathroom on the other side or above.
- Look for mould. Black mould on cold surfaces points to condensation.
- Note when it gets worse. After rain suggests penetrating damp. In winter or on humid days suggests condensation or salts.
If the cause is not obvious, a damp survey will identify it with readings and checks inside and outside, so you only pay for the work that is actually needed.
How to Repair Bubbling Plaster
1. Fix the Moisture Source
Repair the leak, clear the gutter, repoint the brickwork, lower the ground level or treat the rising damp first. Re-plastering over an active moisture source will fail again.
2. Let the Wall Dry
Walls dry slowly. Heating and ventilation help, and a dehumidifier speeds up drying in a closed room. Our guide to whether damp plaster will dry out covers drying times.
3. Remove the Damaged Plaster
Hack off all blown, soft or salt contaminated plaster, usually extending beyond the visible damage. Where rising damp has been treated, plaster is typically removed to a height of around one metre.
4. Re-plaster With the Right System
On salt contaminated walls, a salt resistant render or plaster system is used so that remaining salts cannot push through again. On older solid walls, a breathable lime based system is often the right choice.
5. Decorate Once Dry
Let the new plaster dry fully before painting, and use a breathable paint on solid walls.
Can I Just Fill and Repaint?
Only if the cause was a one off, such as a leak that has been repaired, and the plaster underneath is sound and dry. If the bubbling comes back within a few months, the moisture source or salts are still there.
Get the Cause Diagnosed
Advanced Damp diagnoses and repairs damp across London and the surrounding counties. Our surveyors are FODCS certified and we are a Member of the Federation of Damp. Book a damp survey and we will tell you what is causing the bubbling and what it will take to fix it.
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Frequently asked questions
What causes plaster to bubble?
Bubbling plaster is usually caused by moisture behind the surface, either from rising or penetrating damp, a leak, or salts drawn into the plaster by damp. Paint applied over fresh or damp plaster can also blister.
Can I just fill and repaint bubbling plaster?
Only if the cause has been fixed and the wall is dry. Otherwise the bubbling will come back. Salt contaminated plaster usually needs to be removed and replaced.
Is bubbling plaster a sign of rising damp?
It can be, particularly if it appears in a band along the bottom of ground floor walls. A survey will confirm whether it is rising damp, a leak or condensation.
Why does plaster bubble after a damp proof course?
Usually because the old salt contaminated plaster was left in place. The salts keep drawing moisture from the air and pushing the surface off. Replacing the plaster with a salt resistant system normally solves it.
Is bubbling plaster dangerous?
It is not usually dangerous in itself, but the damp behind it can encourage mould and, if it reaches timbers, rot. It is worth finding the cause promptly.
Reviewed by Michael Young, Head Contractor at Advanced Damp (CSSW and FODCS). Last reviewed November 2026.
Related Case Studies
Our recent work includes flat after a flood, Finchley N3; kitchen and dining room, South Hampstead NW6 and entrance party wall, Kilburn NW6. Each case study sets out what the survey found and how the problem was fixed.
Flat after a flood, Finchley N3
Walls reading up to 64% with heavy salts after a flood. New DPC, replastering and a tanked kitchen floor.
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Kitchen and dining room, South Hampstead NW6
A follow up visit found the first treatment working, with moisture beyond its edge. The DPC was extended.
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Entrance party wall, Kilburn NW6
A raised front step was bridging the DPC. The party wall was treated with a new DPC, render and set.
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Sam Fitzgerald is the founder of Advanced Damp and a working damp and structural waterproofing surveyor diagnosing and treating moisture problems in residential and commercial properties across London and the South East. He is FODCS certified (a Federation of Damp Certified Surveyor) and a member of the Federation of Damp. His hands-on work covers rising damp, penetrating damp, condensation, basement waterproofing to BS 8102, and thermal imaging surveys, and he has personally completed over 400 damp surveys across properties of every type and age. Everything he writes draws directly from jobs he has carried out. He does not write about treatments, products or causes he has not dealt with first-hand in the field.
