"N. Thornton" wrote in message
om...
Fwom:Autolycus )

snip
I have another building of around 120 square
metres which is structurally sound but has a number of leaks in its
big-6 asbestos sheets as well as quite severe condensation problems
on
the underside of the roof. I don't relish removing the existing
sheets,
and I certainly don't relish paying for their disposal.

Does anyone have experience of "oversheeting" with steel, onduline,
or
other materials? I believe it can be done directly onto the sheets,
having first removed all the nails, or onto battens.




Re your 2nd building, I presume cement sheet, which is what asbestos
sheet is, could be cement lined to renovate it. Mixing fibres in for
reinforcemenr would make it behave musch like the asbestos there
already. Presumably one could make a good superstrong mix and trowel
it thinly onto the asbestos already there? Certainly be a big cost
saving.

Assuming that by "cement lined" you don't mean trying to render the
_underside_of corrugated sheet, three problems spring to mind:

Preparation of a moss and lichen-encrusted, slightly friable area of
asbestos-cement sheet to accept a trowelled-on cementitious mix would be
non-trivial: filling the troughs completely, and having say an inch of
render above the peaks would require around 6 cubic metres of concrete -
over 12 tonnes more load on the structure, and a hell of a lot of mixing
and lifting; then, of course, if (when) any cracks do develop through
thermal or structural movement, water could well run down the very
corrugations that are leaking now.

I don't know whether the extra thickness would provide enough insulation
to solve the condensation problem.

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You could either treat the whole roof like this or just spot patch.

Not easy to spot patch _and_ profile it so water running from further up
the roof doesn't pond in a corrugation - and there's still the
preparation problem.

Thanks for the ideas - but I don't think we're there yet.


--
Kevin Poole
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