by StaffsPhil »
Thu Jul 16, 2020 7:27 pm
Reluctant novice painter here encountering a similar problem in our 1970s house trying to cover very old, thick, dark blue - possibly - vinyl emulsion (which I've had to sand back to bare plaster in places) with water-based matt.
Research online suggests bubbling is probably down to an adhesion problem with original paint. I used Wickes plaster paint as a first coat to ensure any of the bare plaster exposed was sealed so I've ruled this out as an alternative source.
Solution suggested in Screwfix forum is to strip back the affected areas to remove imperfections/fill, etc. where needed and then paint with either Zinsser Bullseye 123 (water-based) or Zinsser BIN Shellac to seal the layers below. BIN is the 'nuclear' option; covers anything & everything (like nail varnish!) but it's oil-based so it'll need to be well ventilated, your brush/roller will be a write-off & it's pretty expensive... but then so is 4-5 coats of emulsion when you've scraped it into the bin!
I'm going with Bullseye 123 on mine & will try to update this post with the results.
Incidentally Zinsser CS staff provide really excellent, detailed responses through Screwfix products' Q&A tabs - worth checking them out.