A Type C cavity drain membrane waterproofing system cannot hope to work without some means of taking water away. If water builds up a head against the membrane – IT WILL FAIL.
Gravity drainage works well, where it can be used, but for many occasions a sump is needed, with one or more pumps to carry any water out of the basement, to waste.
I visited a basement conversion site in Leeds the other day – where Brick-Tie Preservation had just installed a Safeguard Sentry 2 system for a client. This is a proprietary automated sump-pump system with two high capacity pumps and a failsafe alarm too. The unit is hidden in the floor of the basement, ready to pump automatically when needed.
The Sentry 2 has a volume of about 150 litres, which can be filled with up to three pumps, should that kind of flow rate be needed. I don’t often use a single pump; two being my preferred minimum. After all, an investment in a basement conversion runs to at least several thousand pounds, even without the kitchen,gym, or whatever is going in afterward, so a few quid for the extra pump is money well spent, just for the peace of mind it gives.
Anyway, for those who haven’t see a sump in action this short video was shot just to demonstrate how fast the pumps can get rid of water. I filled the sump with a hosepipe and switched the power back on. Don’t worry too much about the noise – that was vibration due to my screwdriver falling in and getting trapped under one of the pumps – it was quiet as a mouse once I realised and fished it out.
I come across quite a few basements in and around Leeds, which have membranes with dry linings, but no drainage – sump or otherwise. These are all gambles and when they go wrong; which is often, it means a complete strip out. I’ve recently completed a basement repair in Horsforth where a flood happened because of the omission of a sump.
No drainage under the membrane – no guarantee.