paint is stripping away

[ephemera]

Our house has white set wall and recently we had some patches re rendered after removing some brick fake fireplaces. The paint around the patch is coming away in strips. It just peels off by hand like paper back to the white set. Im not sure if I should peel back the whole wall and start again or should I try to sand the edges of the torn paint and blend them in. Either way do I need to put some sort of undercoat or something on before I actually paint? Where the paint is stripped off as I said the wall is bare plaster(white set). Thanks

[scotthas]

Hi Ephemera

White set plaster normally requires a preparation coat of Sealer Binder before any topcoats are applied.

[getmeouttahere]

Hi Scotthas (and anyone who can help)
I also have white set plaster and I've bought Zinsser Smart Prime which is water-based and claims to have the performance of oil-based. Is this good enough? Some of my walls still have water-based paint and lots of wall filler (Uni-Pro Smooth Coat) on. Can I use Acrylic Sealer (water-based undercoat) on them?

[Ken-67]

If you try to sand acrylic paint the heat created from the sanding (even hand sanding) tends to soften the paint, and more starts to peel anyway. If some has peeled off, it suggests the wall was not properly sealed in the first place, or the white set was not given enough time to dry properly before painting. In either case, it's likely that the whole wall needs to be stripped back, then re-sealed.

[ephemera]

thanks for the responses, I have peeled all the paint off, absolutely hideous job.