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
