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.
How much asbestos it holds
Asbestos cement products typically contain a low percentage of asbestos by weight, most often chrysotile, with the rest cement and aggregate. 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.
Where it turns up
Corrugated and flat sheeting, roof slates, soffits and fascias, gutters and downpipes, flue pipes, cold water storage tanks, cisterns, planters, garage and shed panels, and buried water and drainage mains. In services it can outlast the building it was installed for, which is why utility works still meet asbestos cement pipe.
Working on it
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.
Concrete and blocks
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.