You like eating Aero chocolates? We do to. But bubbles are meant to be kept for chocolates, and should not be on your walls. Here’s what to do if you find bubbles on your walls..
What is Bagging/Blistering?
‘Bagging’ or ‘blistering’ refers to bag shaped blisters on your wall, that are filled with water or other liquid. If they are not intact, they are dried out and perished and flaking. These blisters can range anywhere from 0.5cm to 1m in diameter.
What causes bagging/blistering?
Basically, blistering happens when the top coat of paint parts ways with the coats beneath it. The top coat can even take away multiple underlying coats of paint with it, like a paint stripper. This process is very difficult to predict, and it may happen over the course of a couple of months, or suddenly. Blistering, happens because;
- Too much moisture, has entered or is entering at the back of the paint film.
- The masonry structure has not dried – and you have painted on it.
- the moisture or ‘vapor’ barriers related to the structure, have been designed poorly.
- An uncleaned wall has been primed or painted on – Presence of oil and grease, like that found on kitchen walls, can prevent the paint from bonding with the surface being painted. (for outside walls exclusively Paint Doctor has a wonderful article on this called ‘Importance of High Pressure Washing’.
- Painting just before or after it rains. This can be just as dangerous as painting on a wet wall. Humid days can lead to water filled blisters.
- Using a latex based paint to repaint a surface that is covered in oil based paint. Mixing types of primer and paint on the same wall can lead to problems, especially on exteriors. Heat causes surfaces to expand, and latex and oil paints behave differently in that situation. Ultimately, the latex may take the oil clean off the wall.
- A suitable primer has not been used. Primers prepare the surface to be painted on, grooming the surface to accept a good and steady bond. Though some paints will bond to surfaces without a primer, good primers can prevent bubbles from forming if the paint being used is not compatible with the surface.
- Painting when it’s too hot – above 27 C. In hot weather, the upper stratum of paint may dries quickly, which traps and vaporizes the paint’s solvents. The solvents in turn create bubbles.
Although blistering can occur with just about any kind of fresh paint finish, latex and acrylic paints are often more prone to this problem. They can happen on interior or exterior surfaces, and they’re more likely to arise when preventive measures haven’t been taken.
How to Remove Bagging/blistering
So, although you’ll need new materials to remove the bubbles, you’ll need entirely the same ones you used before to repaint the surface – this is a ‘duh’ moment. To get started, you’ll need a putty knife or paint scraper, sandpaper, cleaner, a couple rags, joint compound and primer.
Then you charge right at it:
- Use the paint scraper or putty knife to scrape the paint bubbles off the wall.
- Sand down the area where the bubbles used to be until the area is smooth and the division between the paint and the wall is seamless.
- Clean the area that you scraped and sanded, removing any grease or dust from the wall.
- Use a joint compound to fill in any pits in the wall.
- Sand the joint compound to make the surface smooth.
- Re-clean after sanding to ensure that dust from the sanding is wiped away.
- Prime area that was just scraped and sanded. Wait for the primer to dry.
- Paint the area that was just primed.
- Wait for the paint to dry, then apply a second coat.
Remember, all of this means nothing if you do not locate the point of moisture ingress, and rectify it. If you cannot rectify the moisture source, a high quality PVC topcoat may have to be applied.
You’ve heard the old age that ‘prevention is better than cure?’ Prevention of paint bubbles requires proper surface preparation before beginning to paint, though there are a few other tricks and tips that may contribute to the cause..
- Do not apply paint over a damp or wet surface.
- Do not paint 4 hours before or after heavy rain – though this is a soft rule and most experienced paint companies will agree that it is very rare to see a rain heavy enough to lift your paint in the 4 hour after period.
- Don’t paint when the temperature is above 28 C. And paint in the shade whenever possible.
- If the surface area you you’re painting on is covered in oil based paint. Use another oil based to repaint it.
- Do not prime or paint an uncleaned wall. Clean, the surface using whatever means necessary. Whether it be a duster, grease remover or household cleaner. Finish it off by drying it with a towel and letting it dry a little longer before moving forward.
- Prime the surface before painting. Primer will ensure that the bond between your paint and the surface being painted is strong and secure.
- Consider a conditioner to help keep freshly applied paint from dying too quickly. Water-based paints are compatible with Floetrol, while Penitrol works with oil paints. These are paint extenders that help improve the paint flow for brush and roller work. Avoid using mineral spirits or water for this purpose; excessively thinned paint only compounds the problem.
So, there you have it, we’ll let you get back to eating your Aero chocolate, and watching your movie.