Basement waterproofing

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8 Feb 2025
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Wanted to ask some advice from experienced waterproofers about keeping water out of my cellar. Existing Victorian cellar excavated down 2ft and new formation build up with DPM, insulation and RC slab. All good until autumn rains and started to get water ingress from one side.
IMG_20260118_190523348.jpg

The above picture is shown on the diagram below. Water is coming from behind the DPM and onto the floor. It will build up to around an inch during the heaviest rains. I knew during excavation that there was a perched water table during rains and that it would drain away after a couple of days. However, the sturctural design, although watertight around the other 3 walls doesn't seem to have catered for this eventuality. The waterproofing strategy was for waterproof concrete shell, but I feel that this eventuality wasn't considered by the engineer (red arrow is the water coming up from between the underpins and behind DPM):
IMG_20260118_190523348.jpg


I have already trimmed back the DPM (this had holes in it so it wasn't possible to lap it up the wall) and tried to fill in the gap with waterproof cement but that hasn't been entirely effective - there's obviously a fiar bit of pressure there.

Any suggestions on how I can approach this? Was hoping I might be able to shutter off 50mm off the bottom of the footings and fill up to the top of footings with a Sika 1 concrete. But this would leave a construction joint and possible weakspot. The second approach would be a sump somewhere, but then I'd have to dig down into my new insulated RC slab!

Any ideas or experience in this area?
 

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