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Posted By Steve P UK
Our school hall (1955) has a mansard roof in asbestos cement, the sheets bolted to steel frame. No sign of damage or even fragility, but the sheets seem to have become porous. A complete re-roofing was sought from the local authority (we chose them as our agents) using insulated steel (trying to use the existing frame), to make a warm roof (and thus avoid the problem of cold-weather bursts from roofspace water supply).
For various reasons, the authority now wants to use a proprietary process to seal the asbestos - but it would involve washing the asbestos (inside and out) and I'm sceptical about draining the water from inside the roof, and about the viability of the asbestos sheets for the process after 50 years in situ.
Am I right to be sceptical?
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Posted By Adrian Watson
Steve,
You're right to be sceptical. Washing the roof potentially causes two problems; you have to get rid of the contaminated water; and you have to consider that process of over cladding the asbestos may result in a contaminated hall.
I recommend you ask them to lift down the asbestos first and then fit a new roof. Don't over-clad the asbestos as you'll have to remove it before you need to replace the roof. If you do you will incur additional costs in the future.
Regards Adrian
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Posted By Dave Wilson
Cant agree more with Adrians comments!! Its a false economy.
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Posted By Steve P UK
For clarification, the authority's proposal is not overcladding but sealing the asbestos with a polymeric membrane.
(It's got a 20 year guarantee, but I'd be worried that H&S regs might within that period require the asbestos to be removed anyway!)
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Posted By Adrian Watson
Steve,
Sorry, I misunderstood. In this case how are they going to preclean the asbestos? There is no good way of preparing the surface for coating. You will have to brush it or pressure jet it clean. If it is brushed somebody has to work on a fragile roof. If it is pressure jetted then it is likely to flake and delaminate.
This is a case where I would strongly advocate replacement.
Regards Adrian
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Posted By Doug Kelly
Steve
I'm sure you will make a balanced judgement on the best way forward with your problem, and have heard of coating AC sheeting as a successful maintenance process. (I would observe that if a company is willing to offer a 20-year guarantee, they must be confident in their product). My understanding of the process is that a biocide is used initially, followed by low-pressure washing - run off water is collected and filtered. The roofing is then coated with a resilient polymer.
However, this process may not be cost-effective when balanced against removal/re-cladding. Something to consider is that if the sheeting is 'failing' it may be vulnerable to e.g. wind damage so coating may be a false economy if it promptly blows off. I am confident though that a 'requirement' to remove asbestos cement is unlikely to be introduced in the foreseeable future - management being the key - so I don't see this as a factor in your decision.
I would not recommend over-cladding - this is notorious for producing contamination of areas beneath - consider how fixings will be applied 'in the real world' - I've been involved in a number of clean up operations after the roofers have carefully smashed the AC to pass bolts through.
All things considered, best value for money will probably be had by removal and re-cladding.
I hope this helps.
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Posted By Robert K Lewis
Steve
A couple of things jumped out here.
a) We chose them as our agent - Are they appointed under CDM 1994 as agent or merely acting as project manager? - In either case they should be working to provide your requirements and suggesting options not imposing solutions which they have determined.
b) Sealing with an external membrane is a good option for a sound roof - but why wash the inside of the material? Are you being given proper information as I would have thought such an action would not be that safe and likely to cause significant internal damage - witness the fire services use of water and the consequences.
c) Are you meaning a true Mansard roof, ie a roof with two different pitches on the slope, or the false one that people confuse it with where two pitches run in together from separate slopes. The first has a single set of complex trusses the second are fairly standard. If a true mansard I have yet to see this effectively done but that may be my lack of use of the system for this application.
d) I cannot, in the light of current HSE views, foresee a defined need to remove all asbestos.
Bob
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Posted By Steve P UK
It's a mansard but the "sides" are almost vertical and the top almost horizontal. (About 13m wide, so a complex steel frame under.)
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Posted By Alan Haynes
A word of caution - there's a deal of difference between Asbestos and Asbestos Cement.
It looks to me as though someone at the council has sen the words 'asbestos cement' and read 'asbestos', and panicked.
It will be so much easier in the long term to remove the sheeting and re-clad. There are plenty of roofing specialists around who are able to remove asbestos cement sheets and re-clad with 'crinkly tin'. Special precautions required during removals are not onerous - not like dealing with asbestos.
Suggest you have a word with some of the major roofing contractors
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Posted By Steve P UK
No, there's no panic, but polymer sealing is being suggested as an alternative to removal and a new metal roof (but I doubt the sealing will solve the issues of fragility and kids climbing on it as well as the asbestos content).
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