Had my walls recently skimmed, put a mist coat on then 2 coats of dulux vinyl matt emulsion on, about a month later, damp marks started coming through. the picture with the hole is where the waste pipe is boxed in, i cut a hole to check for leaks and everything is dry?? so a bit confused. the other picture is of a internal wall, There must be moisture present on both sections. as when i put an electric heater on the marks it disappears but reappears within a few hours. im not exactly sure if it is damp as there are dry spots in the middle of the patches. the skim was left to dry for about a month so dont think its that, anyone have any ideas???? View media item 36444 View media item 36445