What bubbling tells you
A bubble or blister forms when a patch of paint lifts away from the surface beneath it. Sometimes it is small and only on one wall, sometimes it spreads across a ceiling. Pressing a bubble often shows whether there is water or air inside. Either way, the paint is no longer properly attached, and the cause needs finding before it is repainted, or it will happen again.
Heat and moisture
Moisture is the most common cause indoors. Bathrooms and kitchens produce steam that settles on walls and ceilings, and if it gets behind the paint film, the paint swells into blisters. Painting a room that has been steamy, or showering soon after the paint went on, can trigger it too. Outside, painting in strong sun can make the surface skin over too quickly, trapping solvent or moisture and causing blisters. Hot surfaces such as radiators and walls in direct sun can cause similar problems.
Painting over dirt, grease or damp
Paint needs a clean, dry, sound surface. Kitchen grease, nicotine, dust from sanding and general grime all stop it bonding. The new coat sits on top of the dirt and can lift in bubbles. Walls that were still damp from washing, a leak or condensation will push the paint off as the moisture tries to escape.
Incompatible coats
Some paints do not sit happily on top of others. Water-based paint over old oil-based gloss, without sanding and the right primer, often bubbles or peels. Emulsion over a glossy or wipeable finish can struggle to grip. Very thick coats, or coats applied before the one beneath was dry, can also blister. If you do not know what is underneath, a decorator can test a small area.
New plaster
Paint on new plaster can bubble if the plaster was not fully dry, or if the first coat was not a thinned mist coat. Moisture still in the wall pushes against the paint, and the coat lifts. Our guide to painting new plaster explains how to avoid this.
Exterior render and masonry
Bubbling on outside walls usually means water is trapped. It might come from cracks in render, overflowing gutters, a leak behind the wall or the wall being painted while it was damp. Non-breathable paints can make it worse by sealing moisture in. Our masonry and render page explains how outside walls are prepared and which types of paint suit them.
The proper repair
Popping or painting over bubbles does not fix them. The right way is to find and deal with the cause first, whether it is steam, a leak, damp or a mismatched paint. Then the loose paint is scraped back to a firm edge, the area is sanded smooth and feathered in, and cleaned. Any bare plaster or timber is primed with something suitable, then the area is filled if needed and repainted. On a large area it is usually best to strip back more widely rather than patch.
Bubbles on woodwork
On doors, frames and skirting, bubbling often means paint went over a surface that was not keyed, or over old gloss without the right primer. On windows, moisture in the timber or condensation on the sill can lift the paint. Resin from knots can also push the coat up in small blisters. The area needs sanding back to sound timber, knots sealing and priming before repainting.
Ceilings in particular
Ceilings bubble for the same reasons as walls, and also when water has come through from above, such as a leaking bath or roof. Even after the leak is fixed, the stain and moisture need dealing with: the ceiling is left to dry, loose paint is removed, the stain is sealed and then it is repainted. Bubbling across a whole ceiling soon after painting often points to a problem with the surface beneath.
Preventing it next time
Most bubbling can be avoided with good preparation: a clean, dry, sound surface, the right primer for what is underneath, paint applied at a suitable temperature and thickness, and good ventilation in steamy rooms. Let each coat dry as the tin advises before the next goes on.
When to look for help
If bubbling keeps returning after repainting, or comes with damp patches, staining or a musty smell, the cause is probably more than the paint. A damp specialist, surveyor or the relevant trade should look at it before redecorating.
Getting bubbling paint fixed
If you have bubbling paint and are not sure why, send us photos and tell us where it is and when it started. We can look at it, suggest what is likely causing it and repaint it properly. Call Eric on 07872 324935 or use the contact page.