What doesn't Expanding Foam stick to ?

What DOESN'T expanding foam stick to? I want to bridge a gap in the apex of a roof, that foam would droop away from, so need to install a temporary 'shelf' until it has hardened.
Picture here:
https://www.dropbox.com/s/o7czysxiile30p7/Apex-Gap.jpg?dl=0
(Background: this is a barn with fibre cement roof that I had sprayed with foam insulation some years ago, but they failed to seal the apex properly despite claiming that they had. Access is extremely difficult as the barn is full of immovable objects (large lathes, milling machines etc) and the apex is about 15 foot up so it will have to be done in short sections - its about 40 foot long)
Andrew
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On 09/04/2016 09:11, Andrew Mawson wrote:

Idiot boy question: why not accept that expanding foam sticks to most stuff and use as a "shelf" something that you are happy to leave there which won't do any damage if they do fall off in time? Eg lengths cut from polystyrene sheet?
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Just cover whatever you use for "shelving" with polythene or any other thin transparent sheeting as a barrier. Fixed on the underside with drawing pins etc. To save the pins tearing the plastic first reinforce the site of the pins with squares of duck tape or similar.
The worst that can happen is that the barrier doesn't work and it sticks but after pulling out the pins taking down the board and trimming all you're left with are strips of transparent polythene on the foam.
Or it might separate with no problems at all.
As was pointed out in a previous thread all plastics are different, as in plastic sheeting and knowing the precise chemical composition of what you have available, and so it may just be a case of try it and see. ( I could go up in the loft right now and maybe check out some old carrier bags which had been subject to "foam abuse" but there would be little point)
Or maybe treating the polythene with a further barrier.
michael adams
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On Sat, 9 Apr 2016 09:11:07 +0100, "Andrew Mawson"

I'd try well-greased bit of shuttering, such as a wooden plank. Experiment on a small piece first. It would need to be held in place quite firmly to resist the expansion. Even if it did stick, if it was a neat piece of wood, it wouldn't look too bad if it remained up there.
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On 09/04/2016 09:11, Andrew Mawson wrote:

The classic GRP mould release system is to polish the mould with silicone polish, over which you paint white PVA. The resin sticks to the PVA, but that separates easily from the polish.
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On 09/04/16 09:55, Nightjar <cpb wrote:

The trick with concrete shuttering is a mixture of sump oil and diesel (at least in the USA - probably would frowned upon here!)
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On 09/04/2016 09:11, Andrew Mawson wrote:

Cover the shelf in (cooking) cling film.
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On 09/04/2016 10:10, alan_m wrote:

+1
Mike
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On 09/04/16 09:11, Andrew Mawson wrote:

Cling film wrap the shelf - the cling film may or may not stick to the foam, but that would not matter if it stayed up there presumably?
I used the cling film trick around door threshold oak strips when I needed to embed the wood onto 3-4 big blobs of isopon to get a level surface to mount the oak onto.
The oak lifted straight out and the cling film peeled off the isopon leaving a perfectly moulded set of pads :)
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On 09/04/16 09:11, Andrew Mawson wrote:

why not use something covered with a sacrficial polythene sheet. Clingflim or similar.
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"The Natural Philosopher" wrote in message

Thanks for all the suggestions :)
Andrew
I've just worked out roughly that it would take 13 750 mL cans of foam, so maybe not a practical solution. :(
What I need is something like the foam pipe insulation you can get - ie a sausage like shape - that I can push into the gap to seal it. But it needs to be about 6 inch diameter and stiff enough to be poked in and stay with it's own 'gription'
So where can I get 6" diameter stiff foam - 1 metre lengths would be convenient, and i'd need a total of 13 metres of them !
Andrew
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On Sat, 9 Apr 2016 15:04:25 +0100, "Andrew Mawson"

Armaflex who make a lot of the pipe insulation also supply the same material in sheet form . https://www.pipelagging.com/product/371/25mm-Class-O-Armaflex-Flat-Plain-Insulation-Sheet-2m-x-0.5m
You could cut sections out of that roll it up and push it in , they also make a jointing tape and on a clean dry surface that sticks like shit to blanket.
A tightwads option would be to cut up foam camping mats.
G.Harman
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On Saturday, April 9, 2016 at 3:04:21 PM UTC+1, Andrew Mawson wrote:

Dozen cans of foam is under 50 quid

If you can find it, its the postage that will be a killer ;-)
Above can foam and poly layflat tubing usually used for packaging, foam fill in situ..

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On 09/04/2016 15:04, Andrew Mawson wrote:

Quite bizarrely I was just about to post a question as to the "quality" of ToolStation expanding foam as I have 6 new windows to fit this weekend.
http://www.toolstation.com/shop/Adhesives+%26+Sealants/d180/Expanding+Foam/sd2857/Contractors+Foam+12+Pack/p36594
12 cans of gun grade or hand held for £44 (£3.60 a tin)
Bought a gun the other day but ToolStation also do a good price for one.
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Candle wax, oils and greases generally? Brian
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On Saturday, 9 April 2016 09:10:55 UTC+1, Andrew Mawson wrote:

Cling film.
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On Saturday, 9 April 2016 09:10:55 UTC+1, Andrew Mawson wrote:

You have another problem too. Expanding foam turns into one huge hollow bubble if too thick. ie you can't fill voluminous spaces with it.
It needs moisture to go off too. So wet down slightly in the place you out it in.
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On 09/04/2016 09:11, Andrew Mawson wrote:

Maybe an appropriate form of silicone?
http://www.wacker.com/cms/en/industries/chemical/polyurethane/polyurethane.jsp?country=GB&language=en
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cut kingspan with a blunt woodwork saw , jam it in the gap, use a foam gun to seal the gaps
[g]
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OR IS THE GAP AT THE RIDGE FOR VENTILATION?
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