Damp patch on wall - microbore pipes?

3 Oct 2017
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United Kingdom
I've been investigating a room in the house that has had a bit of mould in it on clothes etc. It's a spare bedroom so not often used. I pulled everything away from the walls and found a damp patch on an internal wall. Nothing was touching the wall.
The wall is between two bedrooms in the house, not an external wall and not a party wall. It's a brick cavity wall with no insualtion. The damp patch is visible in this room, but not the adjacent bedroom (but that is wallpapered). Where the damp patch is, it's either plaster or plasterboard onto brick, with whiteish paint on.
The wall paper is visibly stained in a semi-circular region immediately above the skirting board (where the stick is pointing in one of the photos. The stain itself isnot visible). The skirting board itself is dry. The paper is slightly damp to the touch immediately above the skirting board, and the semi-circular bit is clearly visible under the right lighting conditions. The stain extends about 500mm along the length of the skirting board, and extends up the wall by about 300mm in the centre of the damp patch.
I lifted the floorboards to see what was going on. It's a suspended timber frame, no evidence of damp/rot on the joists or boards. The joists are resting on a 'DPC' which is on brick. The overview photo shows a lot of debris on the DPC which I've now cleaned off (see 3rd photo) because I was concerned it was bridging from the damp wall to the joists. Hopefully they're protected now.
I can't see a DPC in the cavity wall itself, and the bottom two courses of bricks (below floor level) are noticably damp. Less damp as you go up, but I can only go up so far until I get to the underside of the floorboards. As I assume there's no DPC in the wall (can't see it) then moisture would easily rise up through the wall and cause what I'm seeing above floor level. Why? Where from?

House was built in 1905, brick cavity walls, externally rendered (looks fine).
The 'floor' underneath the suspended floor looks like tarmac or similar, not sure what. Seems dry.
The damp patch wasn't there when I moved in 2 years ago.
It's on an internal wall, and localised to one spot.
There are microbore CH pipes running through the cavity wall through a gap (second photo). These were partially buried in dust/rubble and are now green. I presume there has been repeated condensation forming on them where they've been in contact with cold brickwork. Dust/rubble now cleared.
No noticable leaks from pipes.
The damp patch is just to the left of the CH pipes through the wall, so not sure if directly related or not.
There is underfloor ventilation from the external cavity walls. However, the gaps in the internal wall (like where the pipes go through) were half full of rubble. Now mostly cleared.

What should I do?

So far:
Cleaned all debris from around the area.
Raised CH pipes up so no contact with bricks/rubble.
Checked for ventilation into underfloor void (air bricks from front of house into cavity wall, another airbrick from cavity wall into underfloor void (lower than outside airbrick).
Dehumidifier locked in the room with windows shut and floorboards back down - damp patch disappears after a few days, only to reappear again.
Heating on in that room at a low tickover.

Should I leave it in the current state slowly drying out, or is there anything else I could/should do now to improve the situation?



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Is this a bungalow is the bedroom or the room on the opposite side of the wall an extension meaning that this wall you refer to used to be an external wall?
Hi, yes it is a bungalow. The wall is an internal wall and always has been.

I looked under the boards at the front/external wall of this damp room last night. Same construction of joists on DPC on brick. Also a LOT of loose rubble and wet dust/silt sitting on the DPC and spilling onto the concrete below. No idea where from... The joists were damp at the ends due to the rubble bridging the DPC they are sitting on. The rubble was also partially blocking air bricks. Digging around it feels like the wall cavity is full of rubble too. All cleaned up now (except the cavity) so hopefully starting to dry out with increased ventilation and less rubbish to hold the moisture. Looks like it isn't related to those microbore pipes after all, and they're probably damaged due to the damp floor void. Might be better asking for advice on another section of this forum?

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