Bubbling, blistering or blown plaster is a symptom, not a diagnosis. It's almost always caused by moisture or the salts that moisture carries, from rising damp, penetrating damp, condensation, or new plaster that's still drying out. The plaster itself isn't the problem: it's reacting to something happening behind it, and painting or re-skimming over it without knowing what that something is just buys a few months before it comes back.
What Bubbling or Blistering Plaster Actually Means
Plaster bonds to the wall behind it and dries to a hard, flat surface. When it bubbles, blisters or "blows" (meaning it sounds hollow when tapped and has separated from the substrate), something is disrupting that bond, almost always moisture or the salts that moisture carries with it.
Where it appears on the wall, how far it's spread, and how old the plaster is are the three details that narrow down the cause fastest, which is exactly what a survey looks at before recommending anything.
Recognise this in your own property? Book a survey or call 07453 527 205.
Why Is Plaster Bubbling on an Internal Wall?
Which wall it's on changes what's likely behind it. An internal partition or stud wall has no direct route to ground moisture or the weather, so blown plaster there more often points to a concealed plumbing leak inside the wall void, condensation where the wall backs onto an unheated space, or salts migrating through from an adjoining external wall at a corner or party-wall junction. An external wall can be affected by rising damp, penetrating damp from outside, or condensation, all covered below.
"Blown," "bubbling" and "blistering" plaster all describe the same thing: surveyors and tradespeople use the terms interchangeably. There's no different meaning behind any one of them.
Why Salt Contaminated Plaster Blisters Again
Bubbling plaster at low level is often linked to rising damp. The salts it leaves behind are a separate problem in their own right, covered in our guide to why salt comes through walls.
A straightforward re-skim over salt-contaminated plaster fails, because the new plaster sits on top of salts that are still hygroscopic, and the same blistering returns within months. The salts are usually present further into the wall than the visible blistering shows, so a proper repair means stripping back further than the damage alone suggests, ideally once the underlying moisture route has been confirmed and fixed. See our guide to telling rising, penetrating and condensation damp apart for how to spot the pattern.
Penetrating Damp and Localised Blistering
Blistering that appears at any height, not just near the floor, and worsens after heavy rain usually points to penetrating damp: water getting through a defect in the building fabric such as cracked render, missing pointing, a blocked gutter, or damaged flashing. The plaster nearest the defect blisters first, often in a localised patch rather than a continuous band.
Fixing the external defect always comes first here. No amount of internal re-plastering holds if water is still getting in from outside. The wall needs to dry out and the entry point needs sealing before any redecoration is worth doing.
New or Refurbished Plaster Drying Out
Not every case of bubbling plaster is a damp problem. Freshly plastered or re-skimmed walls can develop small, scattered blisters in the first few months after the work as residual moisture from the wet plastering process escapes through the surface. This is usually cosmetic, tends to be spread thinly across the wall rather than concentrated in a band or patch, and typically settles down as the wall finishes drying out.
The distinction matters because treating drying-out blistering as a damp emergency (or, worse, ignoring genuine damp because it "looks like the plaster is just drying") both lead to the wrong outcome. Age of the plaster and whether it's recently been redone are the key questions to ask.
Condensation-Linked Plaster Failure
Persistent condensation on a cold wall doesn't just grow mould on the surface. Over time, repeated wetting and drying cycles can degrade the bond between plaster and masonry, particularly on external corners, behind furniture pushed against outside walls, and in poorly ventilated bathrooms. The blistering here is usually accompanied by black mould rather than the white salt crystals typical of rising damp.
Our condensation control guidance covers the ventilation and thermal-bridging fixes that stop this recurring once the affected plaster has been treated.
What Not to Do
- Don't paint over bubbling plaster to hide it: trapped moisture behind fresh paint accelerates the blistering rather than stopping it.
- Don't re-skim without diagnosing the cause first: new plaster over an active damp source fails again within months.
- Don't assume it's "just the wall drying out" if the plaster is more than a year old, as that explanation only really applies to recently plastered walls.
- Don't chip away only the visibly blown patch if salts are present, because hygroscopic salts often extend further than the blistering makes obvious.
When to Get a Survey
If the plaster is more than a year or two old, if the blistering is concentrated at low level or follows a defect outside, or if it's accompanied by a musty smell, tide marks, or mould, it's worth getting a proper diagnosis rather than guessing. Our independent damp survey from £250+VAT uses moisture readings and, where visible, salt marks to confirm the actual cause before any re-plastering is quoted, and where remedial work is needed, our sister company LWR Group carries it out.
FAQ · Frequently Asked
Common Questions
Is bubbling plaster always caused by rising damp?+
No. Rising damp is one common cause, but blistering plaster can also come from penetrating damp, condensation trapped behind a poorly bonded skim, or, on genuinely new or recently re-plastered walls, simply the plaster drying out, which usually resolves on its own. The pattern, height on the wall, and age of the plaster all help tell these apart.
Can I just re-skim over bubbling plaster?+
Not if the underlying moisture source is still active. Fresh plaster over a wall that's still damp or salt-contaminated will blister again within months, because the plaster itself isn't the problem: it's reacting to what's happening behind it. Diagnosing and fixing the cause first is what makes a re-skim last.
How do I tell drying-out blistering from a real damp problem?+
New or recently re-plastered walls can show small, scattered blisters in the first few months as residual moisture from the wet trade work escapes. This is usually temporary and settles as the wall dries. Blistering that appears on older, previously sound plaster, follows a horizontal band, or comes with a musty smell or salt crystals is more likely to indicate an active damp problem.
Does bubbling plaster mean the whole wall needs redoing?+
Not necessarily. Once the cause is identified, only the affected area typically needs stripping back. The height and extent depend on how far the moisture or salt contamination has spread, which a survey establishes before any work is quoted.
Is bubbling plaster a sign of a bigger problem?+
It can be. Loose or blown plaster isn't usually a structural risk in itself, but it shows that moisture, or the salts moisture carries, is getting into the wall, and where it's linked to damp it often comes with mould growth behind or around the affected area. Until the cause is found and fixed the plaster keeps failing, so it's worth investigating promptly. Health is not our field, so for any question about health, use the NHS: damp and mould and your health.
What does "blown plaster" mean?+
"Blown," "bubbling" and "blistering" plaster all mean the same thing: the finish coat has separated from the wall behind it and sounds hollow when tapped, rather than solid. Surveyors and tradespeople use the terms interchangeably, and there's no meaningful difference between them.
What causes plaster to blow on an internal wall?+
Internal partition and stud walls have no direct route to ground moisture or the weather, so blown plaster there is less often rising or penetrating damp and more often a concealed plumbing leak inside the wall void, condensation where the wall backs onto an unheated space, or salts migrating through from an adjoining external wall at a corner or party-wall junction.
Is plaster bubbling on an internal wall less serious than on an external wall?+
Not necessarily. A hidden plumbing leak behind an internal wall can cause more damage than typical external-wall damp before it's noticed, because it isn't obvious from outside and often isn't found until the plaster has already blown. Internal-wall blistering is worth investigating just as promptly as external.
