several grey areas have appeared on the internal joining wall of our first floor bathroom. The patches are high up the wall about a foot below the ceiling in 3 clusters of about 0.5ft diameter. They are 8ft away from the window and external wall of the room. Only the roof space is above.
They dont feel wet, there is no visible condensation and no visible mould. I am very confused about what they could be and how to treat them.
Thank you in advance for your advice.