Dark Spots in Unventilated Spare Room on Outside Walls After Replastering Damp can be a major issue in the home. Find answers to questions or post your own here.

[Dercookster]

Hi, I wonder if anyone could advise a complete novice please. We always had dark spots on our wallpaper for years in an unventilated spare room but were told the wall was not damp following recent tests. We recently removed the wallpaper and replastered the wall and now have damp spots on the new plaster in the same places as we had on the wallpaper. The two walls concerned are both outside walls, the inside walls have dried fine as has the ceiling. I appreciate It's not been long since platering (2 weeks) but I am concerned the marks that remain are in the same places as the marks on the old wallpaper. Are these just taking longer to dry and if so will they eventually dry or do I need to do something before painting the wall. I have uploaded some photos. Any advice gratefully received. Thanks

[welsh brickie]

is the outside wall clear of any debris, like soil etc, it could be cavity bridging, mortar on the wall ties causing damp to bridge across.
The only way to find out is to hire a camera ond drill the wall to look inside the cavity