Short answer
If paint is bubbling or peeling away in sheets, simply painting over it is rarely the right fix. First find out why the coating has lost adhesion. Common causes include moisture, a dirty or greasy surface, a glossy old coating, a weak previous layer or painting before the surface was properly dry.
Moisture is a common cause
Water can enter a wall from a roof, pipe, facade, window joint or condensation. When moisture reaches the back of a paint film, it can reduce adhesion and lead to bubbling, cracking and peeling.
If the damage keeps returning in the same area, gets worse after rain or is accompanied by damp staining, find and correct the water source before repainting.
The surface may be contaminated
Dust, grease, silicone, soap residue and other contamination can form a barrier between the coating and the wall. The paint may look fine at first and then begin to blister or detach later.
The old coating may be too glossy
A very smooth, glossy coating can provide poor mechanical grip for the next layer. It normally needs to be cleaned and dulled, and in some systems a suitable bonding primer may be required.
The coats may not have dried correctly
Applying another coat before the previous one has dried, or ignoring the manufacturer’s temperature, humidity and recoat instructions, can weaken the coating system.
What should you do?
- Check first for leaks, dampness and condensation.
- Remove loose and blistered coating back to a sound surface.
- Clean off grease, dust and other contaminants.
- Dull glossy areas by sanding where appropriate.
- Remove sanding dust completely.
- Prime bare or highly porous areas with a suitable primer.
- Allow every layer to dry according to the technical instructions.
- Apply the compatible finish coat.
Can you just puncture the bubble?
No. Puncturing a blister and painting over it may improve the appearance for a short time, but if moisture, contamination or a weak layer remains underneath, the problem is likely to return.
Common mistakes
- Repainting before fixing the leak.
- Priming over loose paint.
- Painting a greasy or dusty wall.
- Applying a new coat directly over a hard glossy surface without preparation.
- Rushing the recoat interval.
When should you call a professional?
If peeling covers a large area, the wall stays damp, mould is present, or the source appears to involve roofing, facade defects, plumbing or waterproofing, solve that technical problem before treating the paint failure.
Sources
- Sherwin-Williams — Peeling
https://www.sherwin-williams.com/homeowners/how-to/problem-solver/peeling
- Sherwin-Williams — How to Fix Exterior Paint Peeling Caused by Moisture
- Benjamin Moore — How to Prepare Walls for Painting