Trapped moisture
Painting on wet plaster, moisture from cracks, poor roof waterproofing, capillary rise. Water turns to vapour and pushes the film from below.
What Causes Paint Blistering?
It's not a cosmetic flaw - it's pressure beneath the film
A problem hiding beneath the surface
Blisters appear as small or large "bubbles" on the paint surface. On apartment buildings they're most common on sun-facing facades, near rooftops, in moisture-prone areas - often just months after painting.
The temptation is to blame "cheap paint" or "a bad crew". But blistering isn't a cosmetic defect - it's a sign that something is pushing from underneath the film. And that "something" is almost always moisture or heat.
What happens beneath the film
Paint forms a continuous, waterproof film over the wall. That's both its strength and its weakness: if moisture is trapped beneath it, it cannot "breathe".
With heat, the trapped moisture turns to vapour. The vapour exerts pressure. The pressure exceeds the adhesion strength. And then the film lifts - creating the characteristic blister. If the blister bursts, the plaster is exposed to rain and pollutants - and deterioration accelerates.
The four main causes
In every blister we investigate, the cause traces back to one or a combination of four factors. Correct identification determines whether the fix will hold or repeat.
Hot surface
If the surface is too hot (direct sunlight), the outer layer dries instantly - trapping moisture or solvents under an already hardened film.
Non-breathable system
When a low-permeability system is applied on a damp substrate, vapour cannot escape. The film becomes a "lid" - and pressure finds its way out.
Wrong primer
A primer that creates a waterproof barrier on an absorbent substrate without proper curing. Moisture gets trapped beneath the primer - before the topcoat is even applied.
How to distinguish blisters
Not all blisters are the same. Diagnosis is straightforward - just puncture one and see what's inside.
| What you find | Type | Cause | Solution |
|---|---|---|---|
| Moisture inside the blister | Wet blister | Trapped moisture in the substrate | Locate and eliminate the water source |
| Dry air inside | Dry blister | Painting in excessive heat or poor technique | Review conditions and application method |
| Only on one facade | Localised | Sun exposure or a specific damp spot | Local remediation + waterproofing |
The diagnosis determines the solution. If you don't know what type of blister you have, every repair is a shot in the dark.
Proper remediation - step by step
Proper remediation is not a simple patch. A surface fix delays the problem by a few months at best. A technical solution follows a specific sequence.
① Remove
Strip every blistered and delaminated layer. Leaving unstable film behind guarantees the new paint will blister at the same spot.
② Test moisture
Use a moisture meter. Readings above 4–5% mean the wall is still too wet to paint.
③ Find the source
Cracked waterproofing? Failed insulation? Capillary rise? If the source isn't found, the blister will return.
④ Dry
The wall must dry completely before painting. In some cases this requires weeks or months.
⑤ Breathable system
Apply a system that allows vapour to escape rather than trapping it. Silicone or micro-molecular primers are key.
If the moisture source is not eliminated, the problem will return - regardless of how good the paint is.
Prevention: less cost, certain results
Blistering is almost always preventable. It doesn't require a more expensive paint - it requires the right process. Four rules that cost less than a remediation job.
Test before painting
Check moisture before opening a single tin. If the wall is wet, don't paint - full stop.
Avoid direct sun
Don't paint a surface baking in the sun. Apply early morning or late afternoon, never at midday.
Right breathability
Choose a coating system with an adequate Sd value - low enough for the wall to "breathe" without retaining water.
Curing time
Fresh plaster needs 28+ days of curing before it can accept paint. Rushing guarantees blisters.
Related Articles
Why Does Paint Peel? How Does Moisture Affect Paint? Sd Value & Breathability Common Metal Painting Mistakes
Paints for Building Facades
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