The back bedroom has two external walls. In the winter the humidity level is high. Few years ago a decorator put on embossed wallpaper and painted over it. After a few years the wallpaper on the walls that are external started to peel off. The wallpaper on the other walls are ok. This is strange because we never had this issue in the past. I think the decorator applied the paint before the wallpaper paste was set. There is no damp in the room but the dehumidifier tank gets full after a few weeks. The old wallpaper on the external walls have been removed. Plan to fill in any cracks and sand over the whole wall to give it some key for new paint. I have read that you need to apply a few costs of diluted white paint onto the wall so that it can be soaked into the old plaster. If this is the case can you recommend what paint to use? Also read about using pva glue. After I have applied the"undercoat" shall I use a normal Matt paint or a bathroom/kitchen paint? Thanks in advance for any advice given.