Tying DPC to DPM

[MrChamp]

Hi
We have an Edwardian house with solid brick walls and a slate DPC. Looking to install a polythene DPM over the new structural slab and am trying to work out how to tie it to the DPC.

I know the DPC is still intact as I can see very clearly the moisture remaining in the bricks below.

I've thought of using tanking slurry at least 300mm past the DPC to form a complete tank, but I'm worried this could just trap moisture under the DPM and drive it up the wall joint.

So my current thinking is to clean away the lime mortar to reveal the slate, repoint with mortar treated with SBR, then lay DPM and seal to the waterproof mortar with something like CT1.

Thoughts?

 

[tel765]

If the slab in the picture is a new poured slab then where is the underslab DPM? Do you intend to lay a membrane and then float a screed because you have very little height left between slab surface and DPC in the wall. Theres more questions if you want them?

 

[MrChamp]

If the slab in the picture is a new poured slab then where is the underslab DPM? Do you intend to lay a membrane and then float a screed because you have very little height left between slab surface and DPC in the wall. Theres more questions if you want them?

So there's no underslab DPM because this slab is tied in with all sorts of ground beams for new steelwork (there's a large amount of steelwork gone in to remove all ground floor walls). The plan instead is to place the DPM on top of the slab underneath 100mm celotex+50mm flow screed with UFH pipes. Finished floor height will end up about 20-30mm below the DPC.

 

[Notch7]

So there's no underslab DPM because this slab is tied in with all sorts of ground beams for new steelwork (there's a large amount of steelwork gone in to remove all ground floor walls). The plan instead is to place the DPM on top of the slab underneath 100mm celotex+50mm flow screed with UFH pipes. Finished floor height will end up about 20-30mm below the DPC.

just run the new DPM up the wall past the existing DPC -dont disturb the existing DPC.

when you plaster -cut the DPM so it is about 2 or 3 inches above the finished floor level -I would 2 coat plastering but if thats what you want use a stop bead and dont plaster near the floor stop say 2 inches up and leave gap behind skirting

If you are concerned then paint the walls with some drybase first as belt and braces

personally I think you might make more problems disturbing the existing DPC.

and although the DPC and DPM wont be connected there is no way for the damp to get from the "damp side" to the "dry side"

I would avoid using 2 coat plaster system on those walls, its hygroscopic and will pick up any damp and the bricks look a bit cracked -maybe use insulated plasterboard or foil backed on battens

 

[^woody^]

You should not have a floor level below a DPC level.

Extend the proposed liquid DPM up the wall and into a chase cut it to the DPC joint.

 

[MrChamp]

You should not have a floor level below a DPC level.

Extend the proposed liquid DPM up the wall and into a chase cut it to the DPC joint.

Unfortunately we had to dig down to avoid loss of a ceiling height.

Was thinking of using polythene sheet but sounds like liquid could be the way to go.

Finish will be lime plaster+woodfibre board to maintain breathability of the wall.

 

[^woody^]

Just a thought. The problem with new floors and liquid surface DPM, is settlement of the slab and cracking at the wall junction. This settlement can occur over years as the house gets lived in and ground and the internal atmosphere stabilise.

Get specific product advice, or go with thick polythene and tucked in to the DPC. Hide the upstand with some plasterboard and skim over it to blend in with the rest.