Release agent for expanding foam

I suspect rain is blowing under the rather narrow steel ridge capping fitted to one of my barns.
Second hand box section rolled steel sheeting was laid on top of an existing but leaky felted roof. I am now finding that water is making its a way under the steel roofing and through the felt.
There are several possibilities... the sheets are secured with heavy duty roofing nails with a trapped plastic seal. The laps are screwed at 18" intervals but there is no mastic seal. The ridge cap is narrow so rainwater could splash and blow under.
I have in mind to fabricate a template/former in 12mm ply to fit tightly to the roof sheet, pierced with holes to allow conventional canned expanding foam to be fed into the ridge and form a tidy seal. Freehand attempts leave an unsightly bulge and reveals large gas pockets when trimmed.
How do I stop the foam sticking to the plywood? And, how long does it take before full expansion is reached?
Any other constructive thoughts?
regards
--
Tim Lamb

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Tim Lamb wrote:

Mineral oil perhaps? eg baby oil.
IME takes a minute for primary expansion, but it goes on oozing slowly for 10-20 minutes. Temperature might have an effect - the above was 20C.
HTH
--
Tim Watts

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Tim Lamb wrote:

Varnish the ply and then spread a film of cheap grease on it including the holes. Unhelpfully, you possible need to leave it for a few hours. Maybe misting with some water might help to accelerate the cure? Try experimenting.
Bob
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oil of any sort, diesel. Leave overnight to expand fully.
NT
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In message

Hmmm...
I think this is heading back to the *trim off the excess* route.
Using cans rather than a professional gun, I need to empty the can before the foam sets in the nozzle. Now that the suppliers have learned to keep the nozzles under the counter, having a fresh one to screw on is not practical.
There is about 40' of roof to do!
I suppose I could purchase some commercial foam ridge seals. They are normally only 1 ukp each and comparable to tinned foam.
Thanks to all.
regards

--
Tim Lamb

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Tim Lamb wrote:

Normally its squidge and trim.
The foam cuts well with a fine bladed saw - tenon or crosscut.
Or simply put a decorative fascia there to form most of the boundary and use little enough so it doesn't squidge at all.

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pinkgrip drywall fixing foam only expands to double, not ten times, i used it to temporarily fix ridges (for a few years?) and for loads of draughtproofing jobs
On 25/11/11 22:05, Tim Lamb wrote:

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wrote:

Polyethylene film. Bin liner, whatever. Peels off the foam a treat.
Thomas Prufer
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