tanked walls are damp

[junglejim01]

A few weeks ago we started work on our 1960s lean to extension. So far walls have been taken back to stone, rendered, tanked and new insulated floor has been laid. 2 of the walls are partly below ground level and old solid sandstone.

My builder was confident that tanking would ensure that dampness wouldn't get in but i've just returned after being away for 2 weeks and the lower 20-30cm of these walls is pretty damp. I know he applied 2 layers of the tanking slurry. One of the damp walls is going to have stud wall and insulation ontop but i'm worried about the possibility of damp building up behind this causing mould etc and also wondering what to do with the other wall. Any suggestions welcome.

 

[Jackrae]

Dampness could be rising up from the base of the wall rather than seeping through from the outer skin. Some form of electronic or injected damp-proofing may be a solution. You could also tank the inner skin to say 1 metre high but if there's hydraulic pressure, acting from the wall, it might push the tanking off.

 

[fmck]

It's just condensation becoming moisture on the coldest surface in the room. Once insulation & vapour barrier are in it will sort out.

 

[junglejim01]

hmm. i was wondering if that may be the case. Is there any way to tell for sure? Any suggestions for the wall that isn't going to be lined?
Cheers