Emulsion Paint Blistering?

[Trixie2]

Painting over old emulsion. Old paint is blistering and will have to be scraped off and redone!
Any ideas why and what precautions taken to avoid repeat?
Many thanks.

[theshedman]

Chances are that it may have been put on without firstly giving it a mist or watered down coat to seal the walls first and then the emulsion will not adhere properly to them. To stop this happening give the walls a coat or two of emulsion that has been thinned with water. It should tell you on the tin but usually on newly plastered walls by anything up to 50% and on previously emulsioned ones by say 10 to 20%.

[buildersmate]

Could be as above, but it could also be the new coat is reacting with whatever was already on there. A really old painted surface could be limewash, for example, and then this could happen.

I'd be inclined to try sealing it with a dilute solution of PVA and water to seal the surface, though I'm not knocking the The Shedman's suggestion.

[theshedman]

Could be what buildersmate says and if this is the case try washing off where the blisters are and it will come off right back to the bare plaster. If this happens then personally I would remove it all if possible as it will probably blister again if you don't. I don't go down the PVA route, some do though and sometimes it may work. It will seal the walls but can often stop the top coats from adhering properly this is because the PVA will seal any residual moisture on the plaster and may cause bubbling when it dries.

[carrust]

After removing loose paint & washing down apply 2 coats of bullseye primer shown in the linkhttp://www.zinsseruk.com/