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Hi, when we first moved in we stripped the wallpaper off in the bedroom and it was painted yellow underneath directly onto plaster and we painted over it in white Matt. 4 years on we decided to brighten it up but when I put a couple of coats of white Matt emulsion on the walls bubbled all over the place. I scraped the bubbled areas, filled, sanded, washed with sugar soap and applied another coat but bubbles appeared in different places. I've bit the bullet and scraped off all the white paint back to the yellow paint but I don't really want to take it back to the plaster as it was hard enough taking off the white paint so can I apply a base coat/primer directly onto the yellow paint before painting again in white matt? Many thanks

Hi, it sounds as if when you painted the walls the first time you did not put on a mist coat but were lucky in that it didn't bubble, but when you tried it a second time your luck ran out and the first paint you put on started to come away. The first time you did them if you didn't mist coat them the paint may not have adhered to the walls properly as it may have been too thick. If this was the case and you say you have removed all the other paint then you just need to put on a mist coat or 2 followed by a couple of coats of the finish you wish to have. If it is the yellow paint that is coming off then it could be that whoever did it the first time did what I have said and not mist coated first. In which case you could have this happening again when you put the next coat on. If this is the case then you will either have to remove all the emulsion or line the walls before you paint.

theshedman wrote:Hi, it sounds as if when you painted the walls the first time you did not put on a mist coat but were lucky in that it didn't bubble, but when you tried it a second time your luck ran out and the first paint you put on started to come away. The first time you did them if you didn't mist coat them the paint may not have adhered to the walls properly as it may have been too thick. If this was the case and you say you have removed all the other paint then you just need to put on a mist coat or 2 followed by a couple of coats of the finish you wish to have. If it is the yellow paint that is coming off then it could be that whoever did it the first time did what I have said and not mist coated first. In which case you could have this happening again when you put the next coat on. If this is the case then you will either have to remove all the emulsion or line the walls before you paint.

This is not the case.. It happened in my practice as well, mist coat is for for extremely dry places when there is a lot of dust on the walls and for bare dry plaster.. So far it was just once and I don't know the answer how to prevent bubbles

Hi rimce44, a mist coat is not just for newly plastered walls and ceilings. It is often used on walls or ceilings that have been painted before but not been done for a while and so the emulsion soaks in too quickly and can cause this problem as could be the case here or if the walls hadn't been mist coated in the first place it could cause this to happen. If pc6844 gave us a bit more information it may be easier to work out if this is the case.

My 2p worth here. I personally think your problem is the yellow paint, I believe that its is an oil possibly lead based paint for sealing walls back in the day lol. If moisture comes through it can get trapped behing the oil based coat and cause it to bubble. Maybe scraping back and filling added to the problem as when the moisture from the filler dried it could have went behind the oil coat. I have seen this in closes and some old tennament houses also public toilets that have been glossed.

Now you have to remove the whole painted area if bubbles keeps on appearing. Just clean the wall and then paint fresh.