Blistering Paint: What Causes It and How to Fix It

DIY Guide Overview: Identify the causes of blistering paint and find the solutions to fix it. After reading this guide you should be able to eliminate the blistering problem and ensure it doesn’t return.

Bubbling paint on a ceiling.
Example of what bubbling paint looks like.

There is nothing more frustrating than finishing a paint job only to find that you have blistering paint. Blistering paint can appear on a variety of surfaces but is most commonly found on interior walls and woodwork.

But what causes the blistering paint? And how can you fix it?

We’ve put together an easy-to-follow guide to help you identify the cause of your problem and offer professional advice on how to fix it and ensure the blistering doesn’t return.

What is Blistering or Bubbling Paint?

Blistering (or bubbling) paint is a defect where the paint film lifts away from the surface. Bubbles form in these areas due to the lack of adhesion to the surface.

Causes of Blistering or Bubbling Paint (and How to Fix)

Blistering paint can be caused by a variety of issues but the most common, and most likely causes of your blistering paint will usually be:

Moisture within the plaster

If your emulsion paint is bubbling then it’s almost certainly due to moisture within the plaster. Most commonly, blistering wall or ceiling paint occurs on freshly plastered surfaces that haven’t had time to fully dry out before a mist-coat was applied. Plaster can take weeks to fully dry so it’s important to give it time before you apply a mist coat in preparation for painting.

Moisture can also get under the paint film through small cracks and this is especially common if your paint is 5+ years old. As plaster surfaces expand and contract, eventually, even the most flexible paint films will succumb to small hairline cracks. Moisture is able to get into these cracks and weaken the adhesion of the old paint film to the surface and can result in bubbles forming as the moisture tries to escape.

Solution: The solution depends on how much of the surface is blistering. If blistering occurs in just a small patch of the wall then you can simply use a scraper or stripping knife to remove the defective paint film until you achieve a solid line. Once you have done this I recommend using a product called Zinsser Gardz which is a moisture-resistant primer for plaster surfaces to spot-prime the area where the defect has occurred and paint back over it.

If blistering is occurring throughout your paint job then unfortunately you’ll have to go through the rather laborious task of stripping the entire paint film from the surface. Again, you can use a stripping knife to do this as the paint should be relatively easy to remove. Once stripped, apply a coat of Zinsser Gardz and allow it to fully dry before repainting the surface.

Blistering paint on a wall.
Here’s an example of bubbling emulsion paint.

Paint being applied to a washed-down surface before it’s been able to thoroughly dry

Similar to the above cause, if you have washed down your walls in preparation for painting and have not given them an adequate amount of time to dry before you start applying the emulsion, the emulsion will lack adhesion to the surface. This will ultimately result in the paint pulling away from the part of the surface that didn’t fully dry.

Solution: Again, you’re going to want to scrape away the defective coating until a solid line is achieved. Spot prime with Zinsser Gardz if blistering occurs in an isolated section of the surface or remove all of the paint and prime with Zinsser Gardz if blistering isn’t localised.

Of course, it goes without saying that if you wash your walls down in the future, ensure they’re fully dry before you start painting!

Moisture within timber

Like plaster, wood absorbs and releases moisture so it’s important to consider the moisture content of the timber before painting it. It’s possible that the moisture content of the timber you painted was over 20% as this typically results in blistering as the moisture tries to escape during warm conditions.

Solution: Strip the paint from the surface using a wooden paint stripper. Use a moisture meter to ensure that the moisture content is below 20% before priming and repainting the surface.

Example of blistering paint on wood.
Bubbling paint on wood can easily be removed using a scraper tool.

Resin exuding from timber can cause blistering paint

If your blistering problem is located on a wooden substrate then there’s a big chance that it’s occurring due to resin exuding from the timber.

Some softwoods are extremely resinous and if not correctly primed prior to painting will bleed through the paint and cause blistering. As the resin can exude from all parts of the timber, not just the knots, the entire substrate can be covered by this oozing liquid and stop the paint from adhering to the surface.

Solution: If resin exuding from the timber is causing blistering paint on the wood, the best course of action is to apply a coat of aluminium primer. Aluminium primer, as suggested by its name, forms a metallic barrier that effectively stops resin from exuding from the wood whilst still giving the top coats something to adhere to.

Top tip: I would recommend applying the primer with a brush and don’t be shy to use plenty of force to ensure the aluminium primer fully penetrates the wood.

Image of aluminium primer tin

The heat from sunlight on paintwork that is south-facing

Paintwork that is south facing is particularly prone to damage from the sun’s UV rays as it is exposed to the sun for longer throughout the day. Therefore, if you have south-facing paintwork that is inexplicably blistering, this could be the issue.

The heat from the sun can have a big impact on the longevity of paint and if exposed to the sun too often, the heat can draw moisture out from the substrate and ultimately lift the paint from the surface.

Solution: The solution for this is very similar to resin exuding from wood in that you will need to remove the defective paint and measure the humidity within the wood. If below 20%, apply an aluminium wood primer to the surface and wait for it to dry. The primer will create a barrier between the paint and the wood and will stop moisture from escaping and taking the paint with it!

I would definitely recommend seeking out a high-quality gloss or satinwood to coat the wood with – I usually use Dulux’s Weathershield paint system or Johnstone’s Stormshield system. Both are highly resistant to the sun’s UV rays and should last for years as opposed to cheap retail products.