Joining a DPM Sheet and Liquid DPM

6 Oct 2013
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United Kingdom

I have and old stone walled (600mm) mid-terraced house which has some rising damp.
I have hacked off 4ft (vertically) of the old lime plaster and found the screed was damp around the edges of the floor.
I hacked away about 50-75mm (horizontally) of the screed and found the footings of the old wall protrude in about 2" then there is a sheet DPM which has been cut with a knife to the concrete slab level so the screed was effectively bridging over the dpm leaving a path for the moisture to travel vertically to the plaster and horizontally into the floor screed.

I was thinking of applying a liquid dpm over the part of the old footings that protrude into the room but I'm not sure if the liquid dpm will 'bond' to the sheet dpm to create a continuous barrier

Has anyone else encountered this situation and tried this method or am I going about this the wrong way?

Thanks in advance
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The membrane should have been taken up the wall to at least above the screed surface/FFL.

You could lift enough of the screed to form a lapped welt join with the old membrane and a pieced-in ripping of fresh membrane.
How far back you would have to expose the existing membrane to have enough free membrane to make the welt join, would be a site call - say 300mm - 400mm?

However, if the membrane is cut short, and damp persists, all around the room, then it would require a re-think.

Anything else would be working with what you have exposed, and codging in of a length of membrane, and say, liquid bitumen to prime the sub-floor and make a bitumen sealed lap join.

Hopefully, others will come in with their, probably better, solutions.
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Hi Ree, thanks for taking the time to reply.

Can't lift the screed back any more as the DPM is below the concrete slab, and I am reluctant to break that in case I damage the DPM deeper down beneath the slab. So as you say I have to work with what I've got, which isn't much.

I have contacted a DPM manufacturer today to see if they have any advice on ways of bonding a liquid dpm to a plastic one. I suppose that even if they do not form a tight bond it will still be better than what I currently have.

I will post up any information on here for the benefit of all.

Thanks again

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