David321:Handle9: Use an undercoat sealer. In my experience pigmented sealer is best but it's a pain to use. An acrylic is easier and just about as good unless you have stains that you need to seal.
You don't have to put it everywhere, only on raw plaster and gib but if you do undercoat the whole room then lightly sand between coats you get a much better finish than spot sealing.
I was thinking about using a pigmented sealer on my walls, can you explain how it is a pain to use?
Oil based. Very fumey