Oversheeting Asbestos Roofs
 

Fwom:Autolycus )


While investigating the options for replacing the 35 sq metres of
asbestos cement roof that blew away in Saturday's gale, I have
discovered just how expensive asbestos disposal has become. One
local
firm has quoted £50 per sheet if I took it to them, or £850 for a
skip.
Derbyshire County council will only accept 2 square metres at a time
at
their sites.

I'm hoping the insurers (Zurich) will pay for the disposal of the
smashed sheets and the remainder of that roof which is now in a
precarious state, but 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.


Maybe its time for the famous disposal trick? For those so desperately
poor as to be unable to afford a skip, building materials can be put
in domestic trash, a bit each week. Slowly it all goes away, free.
Just bag it in small bags rather than rubble bags, carrier bags ideal.

Asbestos should be double wrapped in plastic before being landfilled,
what the law says about putting it in the household trash I dont know,
cant tell you.

But I cant see this being much of an issue, since your insurer will be
liable for disposal anyway. Unless you decide to settle for cash and
dispose as cheaply as poss.


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.

Strong cement mix:
3:1 is ideal ratio for standar sand/cement only mix.
Add pva for increased adhesion
Add fibres for increased tensile strength and crack control
Add extra fine non-organic silt as well to improve granule packing,
thus increasing both comprssive and tensile strengths.

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


NT

"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.

snip
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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