More DPM?

19 Nov 2010
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United Kingdom
Hi there...

Im about to lay 12sqM of screed in a small extension and Im not sure whether to use DPM or not.

I suspect my hesitance could be as a result of working on a building site nearly 10yrs ago, the screeders used DPM but I think this may of been specifically because of block & beam floors... but wanted to ask the question to be sure.

The floor on my extension is a concrete over site, 150mm (with 142mesh) on 75mm of insulation board on 1200DPM (sand & hardcore beneath). The concrete is tamped to DPC level and I need a 50mm bonded screed to get up to floor level in the house.

The bricklayer cut the DPM level with the house DPC. Do I need to lay the screed directly on the concrete slab or do I need to lay another sheet of DPM before I lay the 50mm screed??

Thanks, Al.
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And if your worried about damp getting past the rather dodgy dpm/dpc join, get some liquid dpm and paint over the join and put some water proofer in the mix.
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the dpm should have lapped the oversite, not cut off.

and no, screed straight onto concrete slab, its good practice to slurry the floor with water and neat cement, use a knackered old brosh for this. Its so the screed adhears to the floor not the dust ;)

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