Causes/remedies for bubbling with fresh coat of paint?

[Windrush]

I have paint bubbles appearing on freshly painted walls.

The walls had a coat of paint with a sheen; it wasn't gloss so it was probably a silk or satin. I sanded the walls down and washed them yesterday. Today I painted a cheap white matt emulsion over it and it's bubbling up in places on two different walls (see pics for examples).

Any ideas what is causing it? I'm paranoid that there may be moisture problems (but there is no evidence of damp or anything).

I have scraped the paint where some of the bubbles are and it is scraping back to the coat of paint that was put on before the silk/satin. What does this mean. How do I remedy the problem? Can I just sand down the areas where the bubbles are and paint over it?

 

[opps]

Whats is the red dot?

More often than not, when applying new emulsion results in bubbles it is the result of the first ever coat of paint not having been thinned sufficiently by the last painter.

You cold sand the walls back or apply Zinsser BIN. It is shellac based and will prevent the moisture from your emulsion re-activating the other paint.

 

[Windrush]

The red dot is a 2p coin, to give an idea of scale.

What do you mean by not thinned properly? Does paint have to be thinned before application?

Also, as I said, it's peeling back to the layer of paint that was put on before the silk/satin. It's not peeling down to the plaster. Well, the big bubble in picture one peeled back to the plaster, but the rest of the bubbles aren't.

 

[joe-90]

Silk is notorious for bubbling. That red dot looks serious.

Best applying a coat of cheapo oil undercoat and then do what you like.

 

[opps]

The red dot is a 2p coin, to give an idea of scale.

What do you mean by not thinned properly? Does paint have to be thinned before application?

Also, as I said, it's peeling back to the layer of paint that was put on before the silk/satin. It's not peeling down to the plaster. Well, the big bubble in picture one peeled back to the plaster, but the rest of the bubbles aren't.

I am still inclined to think that the flaw lies with the very first emulsion. Any bubbles that have not shrunk back will need cutting out and filling (I would use RedDevilOneTime filler and 180 grit silicone carbide paper). After sanding these apply thinned emulsion or WB primer. Then apply your non-waterbased sealiing coat of choice.

Joe's UC will be the cheapest but much smellier and slower drying than BIN.

UC will need a day or 2 to dry before emulsioning, BIN will be the same day.

Both will cause the emulsion to dry more slowly as the water content only has one direction to dry, ie. into the room rather than the wall and room. Opening the windows will speed up the drying (even though it is cold outside).

 

[Windrush]

Thanks for the advice.

We sanded down the bubbles and filled where needed etc.

We've painted the first coat of wall colour on and we have more bubbles. My brother-in-law has been painting at his house today and has had the same problem.

Further investigation (via Google) suggests that bubbles can also be caused by cold walls and the walls are rather cool to the touch, even with the heat on. I've never painted in the winter before so that may explain why I have never had this problem before.

 

[joe-90]

What a load of cobblers. It's the water in the new paint making the previous coat expand that causes it.