Asbestos cement is Portland cement reinforced with asbestos fibre, and it is by far the most common asbestos product in Britain: roof and wall sheeting, rainwater goods, flues, water tanks, pipes, panels and slates. The fibre content is low and the cement binds it, which is why work on it is normally non-licensed and why it is safe while intact. Break it, cut it or erode it and the cement stops binding anything.
What percentage of asbestos is in cement sheeting?
HSE's survey guide (HSG264) puts asbestos cement profiled sheet at 10 to 15% asbestos by content, with the rest cement and aggregate, and notes that some flexible sheets also carry a proportion of cellulose. Chrysotile, used until November 1999, is by far the most common type found in it; crocidolite (1950 to 1969) and amosite (1945 to 1980) were also used in its manufacture. That low proportion is the reason for its regulatory treatment, and it is not a reason to be casual: a broken sheet, a cut with a disc, or a pressure washed roof releases fibres from that matrix regardless of how small the percentage was.
The difference between an asbestos sheet and a fibre cement sheet
By eye there is very little. HSG264 says asbestos cement sheets are visually very similar to the non-asbestos fibre cement sheets that replaced them, and that in older buildings most pre-formed exterior cement sheets can be strongly presumed to be asbestos. The one mark worth looking for is the code near the edge of the sheet where the sheets overlap: replacement fibre cement sheets carry 'NT', and some newer asbestos sheets carry 'AT'. With no code to read, one sample of each type of sheet settles it.
Asbestos cement panels and boards, and its most common use
Its most common use is the one you can see from the road: profiled roofing and wall cladding sheets, sold under names such as Big Six, Double Six and Super Six. HSG264 also lists semi-compressed flat sheet and partition board in farm partitions, infill panels for housing, bath panels, soffits, wall and ceiling linings and portable buildings, and asbestos cement panels in schools as fume cabinets and kick boards. Beyond sheet it was made into slates, gutters and downpipes, flue pipes, cold water tanks, cisterns, garage and shed panels, and buried water and drainage mains, which is why utility works still meet asbestos cement pipe.
Working on bonded asbestos cement
Fixings are undone rather than broken, sheets come down whole, cutting is avoided and where it cannot be avoided it is done wet with hand tools rather than dry with a power saw. Angle grinders and dry cutting are the two things that reliably turn a routine job into a contamination. The waste is still hazardous waste even though the work is non-licensed. HSE treats removal of asbestos cement products as non-licensed work provided the material is carefully handled and removed without breaking up, and that includes sheet that is weathered but not otherwise substantially damaged.
Asbestos in concrete and blocks, and what asbestos concrete really is
Ordinary structural concrete was not made with asbestos, but products described loosely as concrete often are asbestos cement: garage panels, so-called concrete sheds, cills and copings. If a grey panel from the right era rings hollow and is only a few millimetres thick, it is asbestos cement rather than concrete until analysis says otherwise.
Questions people ask about asbestos cement sheet
Is asbestos cement dangerous?
Intact and undisturbed, it releases very little. The risk arrives with breaking, cutting, drilling, sanding or power washing, which is what the handling rules exist to prevent.
Can asbestos cement be drilled?
Drilling is a disturbance and it is discouraged. Where it is unavoidable there are controlled methods for it, and this site does not set them out: the point of the guidance is that a competent contractor does the work.
Is an asbestos cement water tank a health risk?
A sound tank supplying a system is not shedding into the air, which is the exposure route that matters. Cutting one up during a bathroom refit is a different question entirely.
Is asbestos sheet roofing still on buildings, and what should be done with it?
Very often, and the usual advice is to leave it alone while it is sound. Corrugated cement sheet was used on garages, sheds, barns, factory roofs and canopies until 1999, and while it is intact and painted or weathered it is a bonded product with the fibre locked in. What makes it a risk is work: breaking it, cutting it, pressure washing it, walking on it or stripping it. So the sequence for an old sheet roof is a survey first, then a licensed or notifiable removal depending on the material's condition, and never an angle grinder on a Saturday afternoon.