Why paint bubbles and peels

Paint bubbles and peels, most of the time, because there is damp in the wall or because the wall was not properly prepared. The paint stops sticking, forms bubbles and eventually falls off. To fix it, you need to find the cause, scrape, dry and repaint.

Damp in the wall

This is the most common cause. Water, as it tries to leave the wall, pushes against the paint and forms bubbles.

Leaks and penetrating damp: rainwater getting in through the façade, roof, window or gutter.
A water leak from a pipe inside the wall.
Rising damp, on ground-floor and basement walls.
Heavy condensation, in poorly ventilated bathrooms and kitchens.

If the paint always bubbles in the same place, the cause is there. Painting again without fixing the source gives the same result.

Salts in the wall

If you see white powder under the paint that falls off, it is salts, known as efflorescence or, in Portuguese, salitre. They come from water passing through the wall. See our article on efflorescence.

Poor surface preparation

Even without damp, paint can peel if the wall has not been properly prepared.

Painting over dust, grease or dirt.
Painting over old paint that is loose or peeling.
Painting over a wall that is still damp, for example straight after new plastering.
Painting over a very glossy paint without sanding it. The new paint has nothing to grip.
Not using a primer, when the wall is very porous or crumbling.

Problems with products and application

Mixing different types of paint, for example water-based over an oil-based paint, without preparing it.
Thinning the paint too much.
Applying coats that are too thick or without respecting the drying time.
Painting in great heat, direct sun or high humidity.
Using an interior paint outdoors.

Façades are exposed to sun, rain and wind. Near the sea, in Cascais and Oeiras, sea spray is even harder on paint. So, outdoors, it is best to use paints made for façades.

How to fix it

Find the cause of the damp and fix it. If it is a leak or rising damp, ask a professional to assess it.
Wait for the wall to dry.
Scrape off all the loose paint with a scraper, until you reach a firm area.
If there is mould, clean it wearing gloves and a mask.
Repair holes and cracks with filler and sand once dry.
Wipe off the dust with a damp cloth and let it dry.
Apply primer and then two coats of paint, with the drying time stated on the packaging.

Tip: A simple test: stick a piece of masking tape on the old paint and pull it off sharply. If a lot of paint comes away, the paint is not bonded properly and has to be scraped off.

How to avoid it in future

Deal with the damp before painting.
Do not rush. Respect the drying times.
Prepare the wall properly, even if it is hard work.
Choose the right paint for each room and for outdoors.
Ventilate bathrooms and kitchens.
Keep gutters and roofs clean, so water does not run down the façade.

If the problem is large, keeps happening or there is plaster falling off, ask a professional to assess it. Often, what looks like only a paint problem is actually a damp problem.