My mother in law had internal walls skim plastered. Some of the walls were not brick, but not plaster board either, the builder said a name that I can't remember ( council house built in the 60 ' s ) , that used to be used to keep costs down. When getting the old wallpaper off the boards were gouged a bit, the builder painted them with what looked like a glue with sand in it and plastered over.
After leaving to dry, plaster was painted with 50 /50 emulsion and water, prior to one or two top coats of neat emulsion. However, there are some patches on the new plaster that seems darker in colour that the paint will not cover.
Will stain block solve this ? Or what is needed to be done.
Cheers in advance.