Damp in party wall

[MattChan]

I wonder if someone could offer some advice on the best way to tackle some damp proofing in my kitchen extension.

I live in a terrace on a hill and next doors floor is therefore higher than mine. On the party wall between us in the extension the BCO noticed the bottom of the wall is damp

To investigate some exploratory holes were made.

The DPC in the wall was found to be just below my finished floor level and my slab DPM laps up past this.

On the neughbours side of this wall there is the cross section shown below.

From the bottom up there is a "damp" stoney infill that bridges the DPC. Then a layer of polythene that is just butted up to the wall and placed directly on the infill with no blinding. Then their garage floor slab which is butted up to the wall and finally the inner skin of their garage blockwork which is built with a 70mm cavity off of the slab.

What would be the best way to resolve to remove the damp and enable plastering to be carried out?

Would it be to inject a DPC in the mortar joint level with the polythene below their slab? Then black jack from my slab to above this?

 

[Deleted member 292770]

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[MattChan]

that’s one option but i’d use tanking not ‘black jack’.
I’d probably build an independent insulated stud partition. keeping it separate from the wall and well ventilated from outside.

I'm really tight on space so if I could avoid the separate wall that would really help. If I were to go the tanking route would I just apply it in the area shown in pink below and seal it to the DPC? I assume I would also still inject the DPC cream in the mortar bed shown in green?

I managed to get a borescope in the wall and have found that although the cavity is open at the bottom of the wall from the 4th course of blockwork up on the neighbours wall there are glass wool cavity batts installed. There is also a DPC installed in their leaf of the wall a few blocks up leaving me with this construction:

 

[^woody^]

DPM up the wall and dry line.

Don't inject, that's a solution to a different problem

 

[MattChan]

Thanks woody. How high should the DPM go up the wall?

 

[MattChan]

A bit of a weekly bump on this thread

If I don't run the DPM up the entire wall wouldn't any damp from where the DPC on the right hand leaf of the wall is bridged by the infill cause issues on my side?

Or because its a flinty infill rather than soil that bridging things do you just treat it like the bridge isnt there?

 

[MattChan]

@^woody^ sorry to be a pain, how high up should I take that DPM?