Remove bubbled paint

[Rustedroot]

Hi, earlier this year I got some
work done which meant the wall was taking back to mortar and replastered. I think I didn’t wait long enough and painted it when the walls weren’t yet fully dry, as the paint has bubbled in various patches (and for various reasons I know this hasn’t happened due to damp). What is the best way of fixing it? Sanding it all back? Would I have to try do a mist coat?

note is an old building so I don’t want to use any moisture trapping like paints as they aren’t good for old brick walls

Bump

You could try sanding it back and then painting a coat of Zinsser Gardz over it. I’ve used it recently for a few tricky areas and it’s worked a treat. It’s water based so lets the wall breathe I assume.

Was the wall mist coated when it was first painted? And what is behind tge bubbles when you scrape them off, is it pink plaster?

Yes it was, I don’t know what went wrong - the other side where I did the same thing is fine, but that wall (mortar/plaster) dried much quicker, so I assume because of that.

the worst bubbles (which is just two Very small patches, 2cm square ish) have gone right back to plaster when sanded (paint could be peeled off), the rest (tiny bubbles) have a mixture of going back to the layers of paint underneath or tiny spots of the plaster

the overall area of this is v small, 30 by 100cm, with most of the paint across that ok

Thanks! Did you sand back to plaster?

@Rustedroot I haven’t actually had this problem, was just trying to get a better idea of what was going on, but I agree that zinnser is probably the way to go, seems that particular one (Gardz) is likely the best thing to use, their stuff is really good.
You’re going to need to get the bubbled paint off obviously, how much sanding needed is hard to know without actually being there.

@Karmatime did you sand all the way back to plaster for the whole thing? And then paint with zinsser?

I only sanded back the bubbled parts and about 20cm around to get an even surface. Mine was on a chimney breast so I went over the whole of it with Gardz for an even finish. However it’s clear so should blend in if you don’t need to do the whole wall.

Thanks @Karmatime ! Yes it’s not a big area, only two bigger bubble bits go fully back to plaster when sanded, the rest is really just tiny pin holes from the bubbles, so I’ll have a go at sanding and getting it even without having to scrape the whole thing back. Fingers crossed this works! And thanks @Lonelycrab !

I am experimenting with this atm.

A bit of a different problem - removed the wallpaper and scraped off as much paste as possible. The problem is the paint "maps" ie there are areas where the paint is left coated, and other areas where it has come off from the wall leaving the plasterboard exposed.

In the past I have just scraped a thin layer of runny filler over the paint holes, then sanded to smooth and painted over. This time though there are lots of holes so I am trying the gartz. It seems like a kind of very runny glue that seals the plasterboard. It also merges with the old paint, so smooths out the edges where the paint has come away. I dunno whether it will work, have done a small area. Next will try coating with emulsion to see what happens.