How to add length to an existing DPM?

[ILikeDIYS]

Hi, I bought a 6x5m DPM and had it laid for an outbuilding base - then concrete was poured around the footings over the DPM.

Turns out the DPM is too small on one side and just about comes up to where the surface of the 2nd layer of concrete will be (we are doing footings first then 200mm concrete slab over the lot after since it's easier).

I need to add to the DPM but wondering what the best way of doing it is?

Shall I just buy and slice another DPM and concatenate with duct tape, ensuring 100mm overlap?

Can't find my answer searching google.

Thanks in advance.

 

[catlad]

How did you not realise before you poured the concrete!

 

[23vc]

What have you just poured, the foundations?
If so, why is DPM involved at this stage?

But yeah, tape and overlap is how to join.

 

[ILikeDIYS]

I did realize it but had no time to order another dpm from eBay! Concrete had to be done on the day.

Yes foundations with DPM under them... 450mm deep footings but only the first half (250mm) was poured. The remaining 200mm will be poured on Wednesday as an entire slab with mesh, fibres etc...

 

[Bodgedbuild]

I had a liquid screed floor poured throughout my ground floor and obviously had to join DPM in several places. I used a couple of differant tapes but the strongest I came across was Radbar double sided tape which I got from Screwfix. The stuff sticks unbelievably well to polythene!

 

[Notch7]

I did realize it but had no time to order another dpm from eBay! Concrete had to be done on the day.

Yes foundations with DPM under them... 450mm deep footings but only the first half (250mm) was poured. The remaining 200mm will be poured on Wednesday as an entire slab with mesh, fibres etc...

It sounds like you are constructing a raft rather than a foundation or floor slab.

Im confused by you saying half has been poured.......foundations are normally cast in 1 go for strength. Where there is a day joint, reinforcing bars or mesh is used.

In terms of dpm - usually it comes in 25m x 4m rolls and overlaps are fine -I think overlap is mean to be 300mm.

 

[^woody^]

Fold the two edges over twice and then seal it with duct tape

 

[ILikeDIYS]

It sounds like you are constructing a raft rather than a foundation or floor slab.

Im confused by you saying half has been poured.......foundations are normally cast in 1 go for strength. Where there is a day joint, reinforcing bars or mesh is used.

Bro I don't even know what I'm doing! Some people say yes to DPM under the concrete slab some say over the top (under the actual floor).

I'm probably gonna end up doing both.

But the guy I'm working on it with is a builder and said put DPM into the hole before concrete and have 500mm hanging out on each of the 4 sides.

I obviously don't have enough hanging out to make 500mm so need to add on

We didn't do any hardcore... just dig out mud with a deeper perimeter (footings), lay DPM, pour only the footings... and now we have to pour the actual 200mm slab on top against the shuttering.

I did stick a few bits of rebar into the footings so the new bit of concrete will grab to them but probably not enough lol

Either way it's not for an extension or anything, just a summer house with only 1 row of bricks on the perimeter.