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Cash Cash is offline
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Default Waterproofing a cement asbestos roof.

Hugh - Was Invisible wrote:
Our 1960s house has a corrugated roof of what is presumably cement
asbestos.

The roof is intact but there is some water ingress. I suspect this is
due to water entering through joints rather than permeating through
the asbestos cement.

The roof is under a 60 feet high tree and has quite a coating of moss
and twigs. Removing them would be difficult without risking breaking
panels and the moss etc probably cushion the panels against falling
dead branches.
Any ideas of how I could waterproof it from the inside?


Hugh,

My old brain's a bit addled today, but is this the main roof of the house or
an outhouse/garage/shed?

Either way.

If the water is spread over a fair area on the underside, it may well be
condensation rather than a leak which some form of insulation on the
underside of the sheets will sort out - this is a problem I've seen quite
often in the past, especially in some of the old outside bogs that that
were around then (roofed with both asbestos and corrugated tin sheets).

If not, then the only ways to cure the problem is to either:

Clear the moss off and run mastic along the joints, around the rubber
washers under the nails and in any cracks and holes and then give the roof a
couple of coats of clear silicone liquid.

Or renew the sheets - which would be the better job.

Forget trying to seal porous sheets from underneath with liquid
waterproofers or paint, as whatever you use will simply fall off after a
while.

f you are convinced that the joints are the problem, try running one of the
mastics that you can apply on wet surfaces, along the joints on the inside -
I've had some good results with a No-Nails type of silicone mastic called
"Fix All" at around £4 a tube from my local UPVC suppliers [1]
(www.fixall.co.uk), and as a bonus, it'll stick the sheet edges securely as
well.

[1] At well under half the price of the stuff sold in the 'sheds' that
are still around, and under one and half times the price that Focus used to
sell it for.

As an aside to this, I was in a well known 'shed' the other day where
looking for some odd-ball material (failed as usual) where I saw ordinary
silicone mastic, made by another well know company, being sold for £8.50-ish
a tube (and I can by the equivalent from aforesaid UPVC supplier for arround
£2).


Cash