Damp Flank Wall with no effective DPC

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22 Feb 2016
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Hi

My 1880s end-of-terrace house is suffering with rising damp/rising salts in the flank wall & chimney stacks and I'm stumped over how to fix it.

The house was a mid-terrace until WW2 when the house next door was bombed, so the external flank wall was originally built as an internal party wall. Therefore, the slate DPC is just 1 course above sub-soil level - far too low to be effective.

The external face of the wall was rendered with a sand/cement mix (presumably around 1940) and has a concrete 'upstand' at the wall base which acts as a soakaway.

I've received mixed advice from surveyors and builders. An independent damp surveyor recommended I just use a meshed membrane internally, but I would really like to fix the problem rather than just cover it up. He was concerned that the concrete 'upstand' is of structural significance, but I don't see how or why this would be the case.

I'm interested to hear people's opinions on what to do about it.

My current idea is:

- Remove concrete upstand and install a shallow french drain to reduce ground levels and improve drainage

- Inject Dryzone DPC (cream or rods) 3 courses below internal FFL

- Remove cement render (external) upto new DPC level and tidy up with bellcast bead

- Leave brick walls bare below DPC level, repoint with 3:1 lime sand mortar

- Remove moss from 'shelves' of chimney stack and treat with Stormdry biocide

- Rake out and patch up any cracks in cement render

- Spray entire flank wall with Stormdry (breathable microporous sealer)


The questions I have about the process are:

- Should I inject the DPC internally as well as externally?

- What about the rear wall of the old 'shared' chimney stack which is difficult to reach?

- Dryzone cream or rods?

- Is it ok to have a french drain follow the contours of the chimney stack externally (presumably with flexible pipe)?

- Could a french drain create any issues with subsidence from the ground becoming too dry? The house was probably built with no foundations.

- Who would be the best tradesman to have carry out the work? I'm happy to inject a DPC myself but the rest is a bit beyond me.

Thanks in advance,
Joe
 

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