DIY Doctor

Edwardian Plinth Question and is it a Form of Damp Proofing?

Postby Namrogoe » Sat Apr 22, 2017 10:56 pm

Hello - first timer question. I'd really appreciate your help.

I recently bought a Edwardian house (1906, cavity walls), and am slowly getting my head around the nuances of looking after an older property. The ground levels around the house are quite high and, in places, encroach upon the DPC. At the front of the house, the ground (in flower beds, which I have now dug up) exceeded the engineering brick course. However, the property has a plinth at the base of the wall (as can be seen in the pics). I am unsure if the plinth effectively acts as an 'extended DPC layer', and hence ground level can exceed the visible engineering brick. I'd appreciate it anyone could clarify this for me!

If the plinth is not part of the damp proofing of the wall, I presumably need to construct a channel to keep the ground 75mm to 150mm (ideally) below the engineering brick. The challenge is that this would be significantly below the level of the driveway. Presumably a linear drain / French drain-type setup. I'd appreciate suggestions.

Thanks in advance!
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Namrogoe
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Postby HandSlander » Sun May 03, 2020 7:48 am

I'm afraid I'm not the expert that you are looking for but I do have a similar question on this forum for my Victorian, for which I await a response but... I have done some homework.
external-concrete-plinth-but-should-i-remove-t49148.html#wrap

My plinth looks very similar to yours, and appears to be part of a retrofit 'damp proofing' job installed in only 2010 by Kenwood (identified via prior owner records). I'm fairly certain mine is made of cement, but I'm not an expert.

I've spent many hours researching, and from what I understand you need to be looking out for the original slate DPC, which I assume yours is located on top of the engineered brick layer. If there are air bricks that may also be a good place to start as the DPC should be at that level (above or below I can't recall). In my case the air bricks are in the middle of the plinth, so I'm almost certain the render is covering what may be an original DPC.

The link below shows an example of a damp issue due to a cement plinth on a listed building. The solution was to replace with Natural Hydraulic Lime (NHL) as a base with Roman Cement as a finish coat - breathable materials. This gives me hope of an aesthetic solution as I'm sure removing the cement plinth will cause damage to the bricks, which themselves are probably unsightly due to moisture.
https://www.standardheritage.uk/uncateg ... ding-kent/

In regards to your dig-down question I found the below link on DPCs and retro-fit solutions very helpful.
https://www.pavingexpert.com/dpc01

It seems something like the below is best practice if your DPC is near ground level.
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