Why paint peels, flakes or blisters: what to do

Moisture is the most common cause of blistering

A blister is a pocket of trapped moisture. When water vapour behind the wall tries to push through the paint film but the film is too impermeable to let it pass, the pressure forces the paint away from the surface and forms a bubble. That is the mechanism, and it is why blistering shows up most in bathrooms, laundries and kitchens, where steam and condensation are everyday facts.1DuluxView source

It also explains why blistering comes back in the same spot after you paint over it. The moisture source is still there. The new film blisters just like the old one did, often faster, because the substrate beneath is already softened from the previous episode.

Exterior blistering works the same way, but here the water usually comes from outside: rain getting behind cladding through a failed seal, a gap in the flashing, or a cracked render joint. Painting a wall in direct summer sun can trigger it too: the surface film dries before the solvent beneath escapes, trapping vapour and pushing the film off the wall.1DuluxView source Paint makers describe the same pattern from the other side: prolonged sun and moisture are what drive exterior coatings to blister, flake and peel.3TaubmansView source

One quick check: push gently on a blister. If it feels soft or the plaster underneath feels damp, there is active moisture moving. A dry, hard blister that crackles when pressed is more likely an old event that has since dried out. Still needs fixing. Just less urgent.

Poor prep and the wrong primer cause peeling

Peeling (the paint lifting and curling away in sheets or flakes) is nearly always a prep failure. Paint sticks by gripping the surface. A glossy, dusty, chalky or greasy surface has nothing for a new coat to grip. So the new coat sits on top of whatever is wrong with the old one, and when heat or movement pulls at the film, it peels.2DuluxView source

The clearest statement of this comes from the makers. A premium exterior system like Dulux Weathershield is guaranteed against peeling, flaking and blistering, but only when applied to a 'suitable and sound substrate' per the product instructions.2DuluxView source That condition is not fine print. It means the prep is what you are actually buying when you pay for a paint job that lasts. Skip prep, and the guarantee is void before the paint dries.

Wrong or missing primer is the other common failure. A bare or porous surface left unprimed drinks the first finish coat unevenly, leaving thin spots that lift fast. And applying water-based acrylic over an aged, hard oil-based system without the right prep creates two layers that expand and contract at different rates. They pull apart as the wall moves.1DuluxView source 4Dulux TradeView source

Pre-1970 homes often carry lead in old paint: assess before disturbing it

There is one thing that changes the approach before any work starts. Homes built before 1970 often used high-lead paint. Paint made before 1965 could hold as much as 50 per cent lead, according to the Department of Climate Change, Energy, the Environment and Water.5DCCEEWView source Lead is a health hazard. Scraping peeling paint on an older home without knowing what is in it is not a safe DIY task.

The limit for lead in paint fell to 1% only in 1965, then to 0.25% in 1992, and 0.1% in 1997.5DCCEEWView source So the older the home, the higher the likely lead in the original paint. Sanding or scraping it releases lead dust, which you can breathe in or swallow. SafeWork NSW lists removing lead-based paint among the jobs that put your health at risk, and warns lead can harm the kidneys, nerves and brain.6SafeWork NSWView source That is the hazard.

If your home was built before 1970 and you are dealing with peeling or flaking paint, have the paint checked by a licensed professional before any scraping or sanding starts. You cannot tell by looking. Age is the trigger. The appearance of the paint tells you nothing. Once the check is done, a licensed painter can take the right approach to the repair.

Cosmetic or structural: how to tell what you're dealing with

Not all peeling paint points to the same thing. Some is just age: exterior paint that has finally reached the end of its useful life, chalking and lifting in dry flakes. That is a patch-and-paint job, then a full repaint. But some peeling and blistering signals an active moisture source, and painting over that without fixing it first is the expensive mistake.

Signs that suggest a cosmetic repair is the right scope: the flaking is dry and comes away cleanly, the plaster beneath feels firm, the affected area is limited to one patch or a section of trim, and it has not happened here before. A licensed painter can check the surface, prepare it and repaint.

Fix the source before repainting if you see any of these: blisters that feel soft or damp when pressed; peeling or blistering that comes back in the same spot after a previous repair; soft, damp or crumbling plaster beneath the surface; blistering in an interior room that is not a bathroom or kitchen; or peeling that appears mainly around windows, downpipes or roof junctions.1DuluxView source These signals point to a moisture source (a leak, failed flashing, rising damp or poor airflow) that needs a professional check before any painting starts.

If moisture is the cause, a painter will often say: fix that first, let the wall dry out, then call me. That is the right call. A wet wall that dries after paint goes on will blister. Waiting saves you doing the job twice.

What fixing it actually involves

Once any moisture source is dealt with and the wall is dry, the repair is the patch-and-paint job. A licensed painter scrapes all loose and peeling paint back to a firm, sound edge. Sanding over lifted sections is not enough. Everything flaky comes off. That part is not optional, because a new coat over loose old paint is the same prep failure that caused the problem in the first place.

After scraping, holes, cracks and any damaged areas get filled and sanded flat. Then comes a primer suited to the surface: the right product for whether the wall is bare plaster, an old oil system, or a porous exterior surface. Primer is not optional. It is the grip layer that makes the finish coat hold. One or two coats of the right finish go on last.

For larger areas where widespread peeling means most of the old coat is already gone, the job often extends into a full interior or exterior repaint of that wall or surface. What drives the cost is the prep, the area involved, and whether access gear is needed. Use the estimate tool below to get a fair-price range for your walls, then get quotes from vetted painters who will confirm the scope on the day.

If mould or damp staining has appeared alongside the peeling, that is a related problem worth looking at together. See the guide on mould, damp and stains on painted walls before you book the repair. And if the walls also have cracks or holes that need patching first, patching and repairing walls before painting covers what that work involves.

What will the repair and repaint cost?