Plaster mist coat

I would sand down the patch and apply 2 coats of bin 123 to it and paint colour over the top. Hope this would help you

This is usually caused by either salt in the plaster or the plaster not being quite dry. You can apply a 4 to 1 mix of PVA, or a coat of Zinsser Bin stain block on the problem areas, either should do the trick.

hi you have sealed the plaster when its still wet you will need to scrape off all the loose paint and sand down all the areas then i would apply zinsser Gardz to all walls then you will be able to paint all walls

You should have used a mist coat of 70 percent paint to 30 percent water not the other way round. This is what caused the peeling paint as when the mist coat dried it did not have enough paint in it to stabilise and bind the chalky surface of the plaster. Paint peels from a chalky, unstable surface. To get a perfect finish you will need to scrape all of the paint off and go back to bare plaster. Use a sharp scraper at a shallow angle and apply minimal pressure to prevent damaging the plaster. Then, rather than a mist coat apply a stabilising solution to the wall like Zinsser Gardz. You can use diluted PVA as a cheaper option but after all of this effort I wouldn’t cut corners. Apply a coat of good quality trade paint which is suitable for bathrooms to the wall. Zinsser permawhite is a good option. Then put a lamp next to the wall to highlight any areas which may need filling. After filling, sand the filler, paint over the filled areas then apply a second coat to the whole wall.

Just to make it more confusing! If you had complete re-plastering rather than simply skimming, you need a long time for it to dry enough to take a mist coat successfully. There are dedicated primers available for plaster and that would have been the better option because they seal whist still allowing the plaster to 'breath'. I would suggest that you remove what paint you are able to get off and try to feather the edges. Then use a proper trade primer. Simply scraping back and doing a mist coat again may not solve your problem.