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?
The moss will be preventing the free draining, backing up the water, which will then be flowing up the joints. Your only sensible solution, is to get rid of the moss. You could caulk the visible inner ends of the sheets at their lowest points which will help.
To kill the moss run bared copper wire across the roof's higher end, so that the copper sulphate formed on the copper is washed down the length of the roof.
Thanks for the advice re the copper wire. Pity I can't wire up the bricked patios or the block paving drive! Have to be careful what I use to avoid staining.
Thanks for the advice re the copper wire. Pity I can't wire up the bricked patios or the block paving drive! Have to be careful what I use to avoid staining.
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]
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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).
We have a corrugated cement asbestos garage roof of similar age to yours. There is no moss on it, but in heavy rain it leaks around the nail holes, even though these are on the ridges, because the rubber (?) washers have gone hard and no longer make a good seal. Every few years I crawl around on the roof (on boards) applying Unibond black gutter seal generously to the worst leaks. Seems to do the trick.
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