DPM to DPC

[crispy_wafer]

Question on how we join the DPC to DPM.  And is it important if DPM goes over or under the DPC?

 

Build up is Block and beam floor, block work inner walls with DPC sticking out about 12 inches in places.  My floor insulation has arrived and is in a nice big pile, so In order to reduce said pile I was thinking I could get the floor swept, DPM down and start laying out the insulation, or more likely I could task Mrs Wafer with the job whilst I play with stud walls.  I've got a couple of rolls of heavy DPM, loads of double sided butyl tape and plenty of tape for the joins ready to go, but as usual when it comes to the finer points questions start getting asked.  So over or under, is the question?

[Olf]

DPM over DPC:

- DPC is pretty rigid, by the time you finish the roll of double sided tape, it may lift off where you started

- you want  to fold DPM nicely in internal corners / fix in external, so it needs to be on top

[crispy_wafer]

Need some advice on tape, as the tape we have wont hold, A quick play in the build tonight and it just peels straight off when overlapping the dpm to dpc.

[Olf]

https://www.toolstation.com/radondpm-double-sided-butyl-tape/p20591

When I ran out of Visqueen branded I got this in a hurry - apart from lack of a label it looks, feels and works like the branded one, at considerable discount.

 

Though it will not hurt is you wipe wet both bonded surfaces, dust on the build is inevitable and does not help when it comes to sticking things together

[crispy_wafer]

Thankyou.

 

That toolstation tape is the stuff I had, it wouldnt even stick to my fingers, maybe I had a bad batch, or it was too cold or combination...  I'll experiment with a heat gun on it and see if it improves matters. 

[tonyshouse]

Semantic question, should it go on top or underneath the insulation, I always put it on top arguing that there it would act as a vapour barrier too, whereas underneath it could actually collect condensation if it got below dew point down there. 

[crispy_wafer]

Well, applying heat works a treat, a quick blow over with my gas torch and it's stickier than a sticky thing and the dpm has bonded nicely.  This heavy dpm is under the insulation, but was planning something over the top of the insulation too,  i was told something about screed eating the insulation and stopping the insulation from floating when the screed is poured.

[Olf]

  On 08/12/2021 at 16:54, tonyshouse said:

should it go on top or underneath the insulation

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All the manufacturer's detail's I've seen asked for both. Even though in beam and block it is debatable how much damp can cross the air gap underneath

 

  On 08/12/2021 at 18:29, crispy_wafer said:

This heavy dpm is under the insulation, but was planning something over the top of the insulation too,  i was told something about screed eating the insulation and stopping the insulation from floating when the screed is poured

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Yes, the top layer over insulation, including perimeter (if rigid used, not the thin lagging) - those stripes are light and set free immediately, don't ask how I know

[tonyshouse]

Manufacturers don’t pay double for anything, they are out to protect themselves and get away with the unnecessary, I hate waste and doubling up 

 

how long before they ask for a double dpm?