Hi, A bit of background on bullet points for ease of explanation: My property is a 1950's bungalow. The room in question has Marley thermoplastic tiles (yes, they do contain asbestos) stuck down with bitumen adhesive. the condition of the exterior walls is as you'd expect from a property that was last rendered probably about 20-30 years ago! There are some small cracks, some flaked paint and a little bit of repointing on some brickwork on the bottom part of the wall that could be done to improve it. I had the room re-skimmed back in December with the exception of 1 wall where the window is due to a leak. The leak was coming in through the ridge above the window (gable end) down the cavity and out from above the window. Roof was replaced in late Feb and the final wall was re-plastered at the beginning of March. After 7 days to allow the plaster to dry, I have poured Wickes SetCrete High Performance levelling compound over the tiles (used their acrylic primer first, un-diluted, as per the advice from manufacturer) Here's where issues start to appear: When the first lot of plastering was done, I noticed that a corner of the room (exterior walls) took a lot longer than the rest of the room. I could visibly see that the floor was moist but with some good ventilation and warmth from the nearby radiator it did eventually dry. When laying the levelling compound, I noticed that the primer took longest to dry in that particular corner as well. I should note that I made sure the floor was clean and as dust free as I could get it before priming. However, the levelling compound did dry fairly evenly so didn't think too much of it. I have now in the last few days come to paint the room. I have used a 4:1 diluted leyland contract matt (that mix ratio suggested by a decorator friend). The next day I notice that there is section of darker wall in the corner and the floor is visibly moist as I can see a darker shade of grey compared to the lighter shade of grey which the compound has dried in. I applied a second mist coat last night but drew a line across the corner on the floor using a sharpie as I wanted to see overnight how much the line expands or retracts. It has grown by about 2 inches further out from the corner. It should be noted that there was no heat or ventilation in the room until this morning when I took the plastic sheeting off the windows (I have been using a paint sprayer). The radiator is still off the wall so no heat in there. From what I have described, does my issue sound like it could be a penetrative, condensation or rising damp issue? And can anyone give me a few tips to test to try and resolve the issue before bringing in costly contractors.