Joining existing bitumic DMC with new polyethylene DPM

[Olf]

The existing flloor had a layer of bitumen at FFL (over the slab) linking with wall DPC. This is slightly different material, about 5mm thick and a bit flexible, looks like roofing felt. On the floor was about 10mm of solid black stuff. Anyway, the floor is taken up, new DPM will be laid on the blinding layer and I'm thinking how to join it with the DPC: it is trimmed along the wall, so no chance to use any tape. I'm thinking there must be some mastic type solution that woul glue the 2 together and provide reliable seal all round - but can't quite find such. Any hints?

[Mr Punter]

Lap the DPM up 100mm past the DPC.  As long as the DPC is installed so it is sticking out a small amount from the blockwork you will be fine, provided you are above ground.

[Olf]

On 04/09/2021 at 15:23, Mr Punter said:

As long as the DPC is installed so it is sticking out a small amount from the blockwork

No such luck, it is trimmed along the walls:

 

There seem to be pleanty of bitumic liquid damp proof mebranes, but they are intended to be painted on the surface only.

I'm not sure how will they work if poured between the old DPC and the new black sheet with intention to seal the gap however big it may be...

'Bostik Bituminous Mastic All Weather Trowel For Roofs' looks like what I need, though specifically mentions 'roofs' in the name, so I'm a bit cautious.

 

 

[Dave Jones]

On 04/09/2021 at 15:23, Mr Punter said:

Lap the DPM up 100mm past the DPC.  As long as the DPC is installed so it is sticking out a small amount from the blockwork you will be fine, provided you are above ground.

 

pretty much this but blackjack it first then lap the new DPC

 

https://www.everbuild.co.uk/wp-content/uploads/2012/05/BLACKJACK-908-DPM-V1.1.pdf