When paint comes off a wall, the paint is rarely the culprit. It is the visible end of something happening behind it. Repainting without finding out what fails again, usually faster the second time because the wall is now in worse condition. The good news: the failure itself carries the evidence.
First, look at the back of a flake
Pull off a loose piece and turn it over. This one action narrows six causes to two or three.
- Clean paint on the back, wall surface intact — the paint failed to bond. Adhesion problem: priming, contamination, or an incompatible surface.
- Powder or chalky dust on the back — it bonded to a loose layer rather than the wall. The old coating or the plaster was chalking.
- Plaster or putty stuck to the back — the paint held, the substrate let go. The problem is under the paint, not in it.
- White crystals on the back or on the exposed wall — salts. Moisture is moving through the wall.
- Wet or dark on the back — active moisture, and nothing else matters until it is stopped.
The six causes
1. Moisture from behind
The commonest cause by a wide margin. Water in the wall — rising damp, a leak above, rain driving through the exterior face — pushes the coating off from the back. Blisters that contain moisture, or peeling in one defined zone rather than all over, point here. Fix the water source, dry the wall, then repaint. Nothing else works.
2. Painted on a damp or green surface
New plaster painted before it cured, or any wall painted while still wet from washing or rain. The trapped moisture has to leave and takes the coating with it. This is why "let it dry properly" is not a delaying tactic — it is the job.
3. No primer, or the wrong one
Primer is the layer that makes two dissimilar things stick to each other. Skipped on a porous or chalky wall, the topcoat has nothing reliable to hold. It may look fine for a season and then release cleanly in sheets — the classic clean-backed flake.
4. A contaminated surface
Dust, soot, oil, old distemper, mould, or the fine film left by grinding and cutting work. The paint bonds to the contaminant and the contaminant is not bonded to anything. Washing and thorough drying before painting is not optional on an old wall.
5. Painting over an unsound old coating
The new coat is only as good as what it sits on. A chalking old distemper or a coating already losing grip becomes the weak link, and the new paint peels away carrying the old one with it. Scrape back to something sound; feathering the edges is not enough if the surrounding coat is failing.
6. Incompatible layers
Certain coatings simply do not accept others over them. A hard, glossy or sealed surface — an old enamel, an existing waterproof coating, a smooth cement finish — needs to be abraded and correctly primed, or the new material will not hold regardless of quality.
Blistering vs peeling vs flaking
- Blisters — bubbles that lift while the surrounding film stays attached. Almost always moisture or solvent trapped under the coating. Break one: wet inside means water from behind.
- Peeling — the coating releases in sheets from an edge. Adhesion failure, causes 3 to 6.
- Flaking — small brittle chips. Usually an aged coating that has lost flexibility, or a strong film over a weak, powdery base.
Doing the repair once
- Find and fix the water first if there is any. Everything below is wasted otherwise.
- Let the wall dry — properly, over weeks not days, if it has been wet a long time.
- Scrape and wire-brush back to sound material, past the visibly failing area on all sides.
- Wash off dust, salts and contamination. Let it dry again.
- Make good the plaster where the substrate failed.
- Prime the whole area, including sound surrounding coating where the finish demands it.
- Finish, in the conditions the material asks for.
If the wall is going to be textured
All of the above applies with more force. Marble texture paint is heavier than paint and unforgiving of a weak base — it will find a chalky or damp substrate faster than an ordinary coat will, and it takes more material with it when it goes. Read applying texture over existing paint before deciding whether the old coating can stay.