On Nov 25, 10:05*pm, Tim Lamb wrote:
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


Clingfilm stops it sticking. Raid the wife's kitchen:-)

When you start using a can, the foam expands a lot more than the final
bit that comes out. Also in cold weather it expands a lot less and
takes longer to go off. So, can't say, A skin forms on the outside
first usually in about twenty minutes at room temps. The thicker it
is the longer it takes. You can spray water at it to accelarate it
but that affects appearance.
It needs moisture to make it go off. But it still sticks to wet
things.