Damp internal wall (at right angles to exterior walls)

[tvrulesme]

I have an internal wall with damp along the middle and I just can't figure out what is causing it.

 

 

The wall is at right angles to this exterior wall where the dotted yellow line is.

 

I'm 100% sure there are no pipes behind or within this wall. It had some thick plasticy wallpaper covering which has since been removed and has been replastered and decorated.

 

I've checked in the loft and there is no sign of roof leaks and the top of the wall is dry. The opposite side of this wall is bone dry

 

Things I have tried and the reasoning:

 

• Ground levels outside were too high and have now been excavated to well below DPC (If ground levels were too high I would expect the bottom of the wall to be damp, not this middle section)
• Removal of thick plasticy exterior masonry paint. This has been done over the last week or so in preperation for repainting the exterior (using hydrophobic yet breathable Emperor Masonry Paint). My thoughts are that water may have been penetrating the old masonry paint and getting stuck behind
• Gutters cleaned and checked for alignment ~2 months ago

 

Is there anything else you think I should try or to investigate people can think of? This is an old building so tanking or "modern" techniques like injection are frowned upon by the conservation officer. They also seem to be concentrated on DPC issues which I don't think is the issue given the position of the damp

Edited February 21 by tvrulesme

[markc]

Is the internal wall masonry or stud? And is it damp around the light switch or is that just shadow.

[tvrulesme]

3 minutes ago, markc said:

Is the internal wall masonry or stud? And is it damp around the light switch or is that just shadow.

Thanks Marc. Solid masonry. As far as I can see there is no cavity. The damp comes from the right in these pictures away from the light switch and when at it's worst extends across to the light switch but is definately not coming from the light switch side.

 

Just from a safety point of view, the switch is kinetic so there are no live cables in the light switch box

[markc]

This is so strange, cold/damp patches and lines are often cold water or gas pipes buried in the plaster, sometimes old conduits that go through to the outside but I can’t think of any reason for the multi ‘layer’ patches.

[Russell griffiths]

Has the wall had an injected damp course put in and the lower plaster removed and replaced. 
they normally replace the lower half with sand and cement with waterproofing. 
this can cause any damp to to then re appear at the path of least resistance which is the top of the new sand n cement plaster. 
 

just a thought. 

[tvrulesme]

1 minute ago, Russell griffiths said:

Has the wall had an injected damp course put in and the lower plaster removed and replaced. 
they normally replace the lower half with sand and cement with waterproofing. 
this can cause any damp to to then re appear at the path of least resistance which is the top of the new sand n cement plaster. 
 

just a thought. 

Not a bad line of thinking. There was no sign of damp injection being done. As far as I could tell, the bottom half was all bog standard plaster rather than sand/cement. 

Based on this I'm guessing that if I manage to solve any penetrating damp that may be occuring from the exterior, this would eventually dry out and I can just forget about it?

[tvrulesme]

Just found this from the decorator a while back so looks like it's a historical issue....

 

[Redbeard]

 

1 hour ago, tvrulesme said:

Based on this I'm guessing that if I manage to solve any penetrating damp that may be occuring from the exterior, this would eventually dry out and I can just forget about it?

Maybe, unless the plaster has been contaminated by hygroscopic salts pulled from the brickwork, in which case based on my understanding (limited, t.b.h) and experience (many many 19th C houses) is that the more that plaster pulls salts through the more likely it is to do so in future. I guess if you managed to make the wall as dry as a bone then there's nothing to pull, but I might be (nay, *would* be) tempted to hack out and replace that plaster (and a bit around it,) at the same time examining the brickwork for any 'symptoms' (whatever they might be).