DPC, DPM, VCL Detailing

[efunc]

I know this has probably been done to death, but the advice and recommendations also seem to change over the years with introduction of new products, etc. Anyway, my DPC/DPM seems to have been done wrong, but I just wanted to ask what I should do next to make it work.

 

It's a small garden room with a 2 course brink plinth, DPC, and then timber sole plate. The floor is concrete slab, 100mm Kingspan PIR, DPM and then 70mm screed. I thought common practice was to tuck the DPM under the DPC, but mine is the other way around:

 

 

 

 

 

 

 

 

 

I'm about to start taping the insulation around the studwork and then I'm going fully envelope the room with a VCL stapled in place. The question is, how do I treat the transition between the DPC, DPM and VCL at the floor? The DPC edge plunges under the screed, so the DPM comes up over it. Should I bother using a double sided butyl tape to seal these membranes together where exposed? Or should I drop the VCL down the walls and sandwich it between those layers at the floor? Or should the VCL instead be taped over the top of the DPM, so that it is the top layer?

[efunc]

OK, just to reply to my own post, I'm thinking perhaps a bead of some sort of silicon sealant all the way around the floor between the DPC and the DPM that's on top. Then trim away whatever surplus of DPM there is, but when I come to do the VCL around the walls use double-sided butyl tape to join it to the DPM. If this causes the bottom edge to flare out a few mm's with all the tape and sealant there it shouldn't matter because the plasterboard would probably be terminated just above this point. Does that sound about right? 

 

I've order a couple of rolls of Visqueen double sided DPM jointing tape. But my question is, what would be a suitable sealant to use between the DPC/DPM? And on a related note, Is there a preferred expanding foam I should use to close up the gaps beween the studs and the Kingspan PIR?

 

Thanks all.

[Mr Punter]

There are lots of ways to approach this and as it is a garden room, not a Passivhaus, there should not be any issue with what you have done. You can just lap the VCL over the DPM. Staple in place.  I like to leave plasterboard 15mm off the floor, so if you get spills they don't get wicked up.

 

I like the Screwfix pink fire rated gun foam.

[efunc]

Thanks for your reply. After much research I concluded that there's no sealant that can adhere to Polythene properly. CT1 Sealant & Construction Adhesive might do OK, enough to block capillary ascent of groundwater, but would not really stick to it. It's possible that the mechanical weight or the screed would form enough of force to seal the DPM against the DPC under it, so it'll hopefully be OK as it is. I just wanted to trap and water that would be drawn up over the DPC and up the walls so considered some butyl tape. I think just joining the DPC to the VCL is the only real option now though.

[Jeremy Harris]

I don't know of any building-type sealant that will adhere to polyethylene, it has far to low a surface energy to enable most adhesives that set to ever adhere to it for long.  Some non-setting mastics do adhere to it well though.  These are most commonly used to adhere polyethylene rain screens to the inside frame of car doors.    This stuff used to be sold on rolls, with a backing tape, and was generically referred to as dum dum.  I can't for the life of me find dum dum anywhere, but this seems to be similar, but in strips, rather than a roll, and a bit expensive: https://www.frost.co.uk/eastwood-flexible-strip-caulk-dum-dum-replacement/

 

This stuff seems similar, but I'm not 100% certain that dum dum was butyl, so I can't say for sure that it would work the same way: https://www.ebay.co.uk/itm/BOLT-ON-PANEL-SEALER-BUTYL-TAPE-ROLL-STRIP-SEALANT-HEADLIGHTS-CARS-VANS-SEALANT-/251426750877?pt=LH_DefaultDomain_3&hash=item3a8a33c19d

 

I was sure that Sika used to make something like this, but right now I'm struggling to find it.

[MikeSharp01]

29 minutes ago, JSHarris said:

I can't for the life of me find dum dum anywhere, but this seems to be similar, but in strips, rather than a roll, and a bit expensive: https://www.frost.co.uk/eastwood-flexible-strip-caulk-dum-dum-replacement/

That link points at a 98 strips 12" long so quite a bit of caulk for £26.

 

 

[A_L]

4 hours ago, efunc said:

After much research I concluded that there's no sealant that can adhere to Polythene properly

 

How about Orcon F?

 

https://www.ecomerchant.co.uk/pro-clima-orcon-f-adhesive.html

 

https://proclima.com/products/bonding-agents/orcon-f

[efunc]

2 hours ago, A_L said:

 

How about Orcon F?

 

https://www.ecomerchant.co.uk/pro-clima-orcon-f-adhesive.html

 

https://proclima.com/products/bonding-agents/orcon-f

 

Good grief! That's a good find! I'm going to hunt this down pronto, thank you so much! I'd looked at at least 20 different sealants and all gave up on Polyethylene. Only 3M were working on something it seemed, but I gave up on the concept. If Orcon F is a genuine solution then that would be wonderful, and a good price too. 

Edited September 19, 2019 by efunc

[efunc]

Hmm.. my chemistry is not great, but the description says it contains alcohol and solvents. Isn't that supposed to degrade polythene? It does say it can bond PE/PA/PP and aluminium foils, but perhaps someone with more knowledge can reassure?

[efunc]

This is a semi-wet mastic used for sealing polythene membranes and VCLs, but it's only available in Canada. I was looking for something similar in the UK, but nothing yet:

 

https://www.lepage.ca/en/lepage-products/build-things/sealant/pl-construction-sealant/pl_acousti-seal_vapourbarriersoundreductionadhesive.html

[Onoff]

What about Green Glue? That stays a bit sticky. Not used myself but seen on site. They were soundproofing with it but said it was fireproof too. Bloke said "it never really drys".

 

The applicator guns look a bit longer than normal maybe and were branded I'm sure. 

 

Or Everflex AC50? Toolstation do that. That "drys" very stretchy.

[Jeremy Harris]

7 hours ago, efunc said:

Hmm.. my chemistry is not great, but the description says it contains alcohol and solvents. Isn't that supposed to degrade polythene? It does say it can bond PE/PA/PP and aluminium foils, but perhaps someone with more knowledge can reassure?

 

Polyethylene is very resistant to most solvents.  I have 5 litre PE cans here containing toluene, isopropyl alcohol, methanol, monoethylene glycol, methylene chloride, plus a few others, and all are fine.  Offhand I think that only solvents like benzine, and maybe napthalene and a few other polycyclic aromatic solvents, slightly degrade PE by tending to harden it.

[efunc]

Thanks for all the great suggestions, several more options than I thought. pro clima Orcon F seems the most suitable product, but at £10-15 delivery most suppliers want for a single tube it's a shame there isn't a local source in London. Green Glue also looks like it could do the job. Everflex AC50 is more for kraft paper lined drywall, so probably needs porous substrate. I looked at polytunnel repair tape and Polythene Jointing Tape which looks perfect too, however is most likely designed to remain in place for only a couple of years, at best, before failing. Certainly not up to the lifespan required for construction, but who knows...

 

I might have to swallow the pill and fork out for the pro clima Orcon F delivery change, but need it by tomorrow now, so it's a gamble. 

 

[Jeremy Harris]

I've used lots of polytunnel tape over the years (mother had polytunnels at the farm).  It only has a limited life, maybe 5 to 10 tears at the most.  I'd not want to rely on it for something hidden within the structure of a building, TBH.