Could anyone advise what is going on here please. These water marks have appeared in the corner of the bedroom wall. They are not wet to touch just slightly cooler. The outside wall is pebble dashed. I’ve had a dehumidifier running for a week and the drum is full every time. It started on 75 and has come down to 40, if I shut it off for a few hours it goes back up to 55. Many thanks in advance.
