Damp marks next to retaining wall

[whathim]

I have some “damp marks” on the lower outside face of the rear of my house, which I think might be coming from an attached boundary retaining wall.

Untitled

• whathim
• 20 Mar 2012
• 1

My house is a 1920’s terraced house on a hill road. My neighbours’ house is set 9 bricks higher than mine and at the rear of our houses there is a single brick thick retaining wall on the boundary between our back gardens (the wall used to be the “party wall” of back-to-back coal bunkers). The ground area on my side of the retaining wall has been concreted over and likewise on my neighbour’s side about 490 mm higher.

My first thought is that the damp is coming from the retaining wall. This wall is attached to the rear exterior wall of my house (it was built like that) and I imagine it is drawing moisture from the higher ground behind it and “wicking” it into the rear wall of my house. Strangely I see no damp marks on the retaining wall itself although there are signs of efflorescence. Inside the house, this corner is largely hidden by kitchen worktops/cupboards and I can see only slight visual indications of dampness.

A complication is that the rear step of my backdoor bridges the DPC (I blame this on previous owner’s DIY) and this I intend to rectify. However, I don’t think this is a major contribution to the damp marks because I see no such marks on the other side of the back door.

My question(s):

Where do you think the damp is coming from and can I do anything about it, short of digging up next-doors patio area of course?

The existing concrete surface is slightly above the house DPC and a gap has been left between the concrete and the rear of the house to avoid bridging. The concrete extends right against the retaining wall and, even though I can see no DPC here, would it be worth my while cutting a similar gap?

Would it be worthwhile considering injecting (I’ve seen this advertised) a vertical DPC right in the corner between the rear of my house and the retaining wall?

Keith

 

[^woody^]

Those stains on the back elevation of the house cant be related to the boundary wall. They look like distemper or some other stain/reaction with the paint rather than isolated damp patches

Anything on the actual boundary wall can't be dealt with without a proper barrier on the other side of the wall and a DPC in the wall to stop damp coming through and up

 

[whathim]

Thanks for your reply. That’s interesting. I must admit I had always assumed they were somehow connected to the difference in level between our two houses – the marks extend up the wall by 9 bricks, which is exactly the difference in level between our two houses.

They have always been there since I bought the house (10 year). On occasions, I have distempered over them but they reappear.

 

[^woody^]

There may be some minerals or iron/charcoal in the clay bricks which is reacting with the paint at those locations, if so a stain block would need to go on the bare brickwork before painting

It seems unlikely that any damp would travel horizontally from the boundary wall to that place at the side of the door without showing more near the corner

 

[whathim]

What you say about it being unlikely that damp would travel horizontally from the boundary wall to the side of the door without showing more near the corner makes sense to me. Also, the only indication of damp inside the house that I can see is adjacent to the door (on both sides) and so may be due to the doorstep bridging the DPC. Hopefully, this will be cured when I remedy the bodged step.

Again, thanks for your help.