Bridging DPC to DPM

CoolhandPete · 14 Jun 2019

During the build of our extension the builder built the walls (outer and inner) before laying the slab. This means the DPM does not go under the course of blocks containing the DPC.

Is this a normal practice these days?

There is also a gap between the end of DPM in places and the DPC, can this be joined effectively to provide a complete damp proof barrier?

Image attached.

thanks in advance.

Notch7 · 14 Jun 2019

Dpm can just run up the wall past the dpc.

The dpm needs to be higher than the top of the screed -after screeding it can be trimmed flush

Dpm can be joined with adhesive tape -it should have a decent overlap.

I think theres an argument both ways for the dpm running across the blockwork with the dpc - the dpm is smooth and and it can be argued it introduces a slip joint. Dpc is ribbed and must be have mortar either side.

The biggest problem with dpm is generally the corners or returns

23vc · 14 Jun 2019

Normally if done like that I thought you’re meant to leave an apron dpm lapped onto the dpc, say a foot wide, then when the slab gets poured tape it to the big dpm.

CoolhandPete · 14 Jun 2019

Notch7 said:
Dpm can just run up the wall past the dpc.

The dpm needs to be higher than the top of the screed -after screeding it can be trimmed flush

Dpm can be joined with adhesive tape -it should have a decent overlap.

I think theres an argument both ways for the dpm running across the blockwork with the dpc - the dpm is smooth and and it can be argued it introduces a slip joint. Dpc is ribbed and must be have mortar either side.

The biggest problem with dpm is generally the corners or returns

Thanks Notch7 that's very helpful.

CoolhandPete · 14 Jun 2019

23vc said:
Normally if done like that I thought you’re meant to leave an apron dpm lapped onto the dpc, say a foot wide, then when the slab gets poured tape it to the big dpm.

Thanks 23vc.
That could well be what he has done.
The dpc on the inner is much bigger than a block width and could well be a foot wide.

CoolhandPete · 14 Jun 2019

Thanks to both replies above.

Is it a special damp proof tape that he should be using?

23vc · 15 Jun 2019

Probably, but I’ve used duct tape.

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Bridging DPC to DPM

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