sticking membrane to PIR

[Tom]

Hello all. Woke up in the small hours pondering this, I plan to cap our nudura walls with PIR laid flat and cut at an angle and want to stick a waterproof roofing membrane (eg https://www.toolstation.com/sark-it-non-breathable-membrane/p26933?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dc&pcrid=&pkw=&pmt=&gclid=EAIaIQobChMI15f627vO_QIVd4BQBh0j8gwcEAQYASABEgKkJ_D_BwE&gclsrc=aw.ds) on to this - what adhesive would work on both the foil face and the cut edges of the PIR? Would a solvent-based impact adhesive do the trick?

[Tom]

😟

Any ideas? Are any specific adhesives to be avoided with PIR?

[crispy_wafer]

I think you can get a suitable double sided tape from someone like Tyvek or even a DPC bitumen tape, guess it depends on the application and what you actually want the membrane to do, the only thing I'm not sure about is how receptive the cut ends are to an adhesive tape, the ends may need to be wrapped with something first.

[Mr Punter]

You may be better with tissue faced PIR which is used for bonding roof membranes.

[DC5]

Hi, there are probably better off the shelf products.

Do you have a sketch or pictures of the build up?

something like Alutrix or Sigawetguard sound more suited.

what’s the next layer over that?

[Tom]

Sorry @DC5, only just saw your reply. The Alutrix looks like it might do the trick, but is considerably more expensive than a simple membrane and tin of contact adhesive and I'm not sure if it would be overkill.

The wall/roof junction is a bit of a pain to detail right, not least as we are going to fit a hidden gutter, the build-up goes something like this:

 

1. Gap between composite roof panels and top of nudura walls filled in with PIR, the membrane in question then bonded over this to make as weather tight as possible.

 

2. The composite roof panels then have battens fixed to them, the folded gutter profile fixed to the ends of these, a counter batten over the top and then corrugated steel roofing sheet to finish.

 

3. Finally, batten - which also supports the outer edge of the gutter, counter batten and vertical timber cladding to the wall.

 

Simple, eh? The membrane bonded to the PIR shouldn't be doing much work, the void should be totally covered by the gutter profile and if the gutter blocks and overflows it should go over the front lip and down the wall (I'll be putting another membrane up the vertical batten and under the front lip of the gutter).

Any thoughts?

 

[jamiehamy]

I doubt you'll get anything that will bond well to cut PIR - it's dusty and porous. EPS would be far better for this but will still be a challenge because of the rough cut edge. . 

 

That's a complex design and makes be wince to look at if I'm honest (and would rather just put it there for your consideration. 

 

What does the composite joist/roof section bear on and how is it tied down?

Is a hidden gutter a real imperative? If so, it might be worth considering something a bit more robust, like forming the channel from timber and using EPDM to bond to the composite panel, down and line the channel and back up and over the batten for the cladding. You would still need the membrane protection underneath but you can get very long pieces of single rubber - you'd probably only need 400mm strips but that should be no bother to obtain. 

 

The design you have I think is inherently flawed - your assumption that water overflowing would go down the front is wrong - wind will blow it back. 

 

[Tom]

11 minutes ago, jamiehamy said:

What does the composite joist/roof section bear on and how is it tied down?

The composite panels sit on steel rafters and Z-purlins

11 minutes ago, jamiehamy said:

Is a hidden gutter a real imperative? If so, it might be worth considering something a bit more robust, like forming the channel from timber and using EPDM to bond to the composite panel, down and line the channel and back up and over the batten for the cladding. You would still need the membrane protection underneath but you can get very long pieces of single rubber - you'd probably only need 400mm strips but that should be no bother to obtain. 

 

The design you have I think is inherently flawed - your assumption that water overflowing would go down the front is wrong - wind will blow it back. 

 

We're too far down the road with the hidden gutter to turn back now! My drawing does look complicated, but it looks a bit simpler in real life...

I can easily lower the front lip of the gutter to encourage any overflow out the front - and likewise the "tail" going up the roof is a good 200mm.

 

 

[jamiehamy]

ah, makes sense! Yeah, but EPS or XPS more likely to take a bond than the cut PIR I would say. 

 

That roof ain't going nowhere!

[JohnMo]

I think I would simplify the insulation shape, so you eliminate the void below the gutter.  It's just going to fill with debris, however hard you try to stop it.

 

The small triangle make more square so it sits just under the gutter, the piece under that also becomes more simple.

 

Where your membrane mets the composite roof panel, you need something with a long life and remains sticky otherwise you will end up with is leaks. How about butyl tape?  But better just eliminate the membrane idea and do the whole lot in butyl flashing.

 

Or do it properly with lead, so it will last a life time.

[Tom]

2 hours ago, JohnMo said:

Or do it properly with lead, so it will last a life time.

Aaaghh! There's a total of about 60 linear meters to do!

 

I'm thinking that where the membrane comes up the end of the composite panel I could just chase it in - a cut along here with a circular saw and tick the membrane in?

[DC5]

Sorry forgot to sub to this.

 

I see the details now, I’m sure there will be a cheaper alternative to alutrix i will have a look.

 

someone mentioned the PIR being dusty to stick an adhesive vcl to which is valid from my own experience this week for something else.

 

I would knock the dust off with a brush then stabilise with something - maybe pro clima sprimer would work?!

 

https://insulationmerchant.com/collections/walls/products/pro-clima-tescon-sprimer-spray-can-primer-750ml?_pos=1&_sid=8b30d352a&_ss=r

 

 

[DC5]

What about this!?

 

https://www.roofingoutlet.co.uk/products/elotene-dsn-self-adhesive-vapour-barrier-10m?variant=39417717227591&gclid=EAIaIQobChMIsKW-2bn__QIVPIBQBh0fawl_EAQYASABEgIhGPD_BwE

[Nick Laslett]

On 09/03/2023 at 08:51, Tom said:

Hello all. Woke up in the small hours pondering this, I plan to cap our nudura walls with PIR laid flat and cut at an angle and want to stick a waterproof roofing membrane (eg https://www.toolstation.com/sark-it-non-breathable-membrane/p26933?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dc&pcrid=&pkw=&pmt=&gclid=EAIaIQobChMI15f627vO_QIVd4BQBh0j8gwcEAQYASABEgKkJ_D_BwE&gclsrc=aw.ds) on to this - what adhesive would work on both the foil face and the cut edges of the PIR? Would a solvent-based impact adhesive do the trick?

Hello Tom,

 

What did you use in the end to stick to the PIR?

 

I have some Pro Clima primer. 

[Tom]

I used an impact adhesive in the end - this stuff: https://www.toolstation.com/evo-stik-contact-adhesive/p95550?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dc&pcrid=null&pkw=null&pmt=null&gad_source=1&gclid=EAIaIQobChMI4-Sox92RgwMVzMbtCh0TygmIEAQYAyABEgJMPvD_BwE&gclsrc=aw.ds

 

Seemed to do the trick, less so on the cut PIR but seemed to hold sufficiently