Anyone seen anything like this before?

[floorboard10]

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

 

[BBSBuilding]

cant see the situation properly but you may need an air vent in the void that houses the pipes. if you block off a chimney stack you need an air vent in the wall so could be the same here.

 

[floorboard10]

Hi, i cut the hole in and marks were still there, exactly the same type of patches on the other wall too and that is a solid internal wall(joined onto a external wall) so dont think its condensation, may be wrong though

 

[BBSBuilding]

have you checked above for roof/pipe leaks?

 

[floorboard10]

Yeah, this is the ground floor, and nothing obvious is standing out, the rooms above is dry, never had issues with damp in there before

 

[hotrod]

That's on the chimney breast, so logically you need to get up there and check the pointing / flashing as the first port of call.

 

[iandandav]

Any water pipes in there? If so might it be water condensing on the pipes, and if the pipe is touching the plaster board it might be soaking through.