Damp patches in newly plastered wall

[erikwoolf]

Few of the external walls of the house had damp issues. We removed the old plaster and did remedial work externally. Most walls are fine but in a couple of places there seems to be damp patches coming through the new plaster. In the photo below you can see them in the lower left corner and along the edge of the new and old plaster. The dark grey stuff is the new plaster it is Diathonite Deumix. This part of the wall was particularly bad and looked like previous owner had tried a few things including some sort of black bitumen material that we have since removed. Any thoughts why we are still getting damp patches despite having removed all old plaster?

 

[a twig]

I would say that it is doing its job and letting the moisture out - the trick now is to find the source.

There is a chance it is residual damp drying out, but given the location it looks like it could be tracking down the wiring for the socket so I’d follow that and see where it leads

 

[erikwoolf]

I would say that it is doing its job and letting the moisture out - the trick now is to find the source.

There is a chance it is residual damp drying out, but given the location it looks like it could be tracking down the wiring for the socket so I’d follow that and see where it leads

Weird thing is that as far as I know there are no pipes or potential sources of leak where these are. It has been very cold in that room though as we had issues with the heating and humidity levels have been generally high. I was wondering if you can still get hygroscopic salts causing issues on a wall that has been brought back to the brick and replastered?

 

[a twig]

I’ve had efflorescence in the past when patching damaged gypsum with lime, but that doesn’t look like what you have done

 

[erikwoolf]

Few of the external walls of the house had damp issues. We removed the old plaster and did remedial work externally. Most walls are fine but in a couple of places there seems to be damp patches coming through the new plaster. In the photo below you can see them in the lower left corner and along the edge of the new and old plaster. The dark grey stuff is the new plaster it is Diathonite Deumix. This part of the wall was particularly bad and looked like previous owner had tried a few things including some sort of black bitumen material that we have since removed. Any thoughts why we are still getting damp patches despite having removed all old plaster?
View attachment 12016

So after a few weeks and when the heating finally came back on this patch and few others have now completely dried out. I have one remaining area though that has been damp despite removing the old plaster and replastering with lime. It has been left to dry since the summer, probably half a year now but still not completely dry. There is nothing externally that will cause the damp, ground levels have been lowered, there is no rain reaching that wall and no pipes. Could it really be that it takes that long to dry? If it is salts should I go ahead and install woodfibre insulation? I have delayed finishing off this wall to allow it to dry out before I finish the insulation but I am kind of losing hope that it will improve.. The biggest patch has a weird inverse L shape.

 

[ChrisW]

Interesting...looks like residual damp...how's things under the floorboards there?

 

[erikwoolf]

Interesting...looks like residual damp...how's things under the floorboards there?

Dry, the floorboards were actually up until recently as we wanted to clean the area from accumulated debris over the years and pass new electricity wires through. I just can't get my head around it. If I knew that I could go ahead and put insulation on and that it would be ok at least I could get on with things and just assume it will take more time for it to eventually dry out