Asbestos cement sheet is grey, hard, brittle and a few millimetres thick, made flat or corrugated. It weathers to a duller grey or a mossy green, sounds dull when tapped rather than ringing, and breaks with a fibrous edge rather than a clean one. Modern fibre cement, which replaced it, looks almost the same, which is why the date of the building carries more weight than the appearance of the sheet.
The corrugated profile
The classic profile is a deep, widely spaced corrugation used on garages, sheds, workshops and farm buildings, fixed with hook bolts or screws through the crown with a washer and a cap. The sheets are surprisingly light for their size and are fragile, which is what makes them dangerous to walk on and easy to break while handling.
Flat sheet
Flat asbestos cement sheet was used for soffits, wall linings, panels beneath windows, garage panels and partitions. Painted, it is indistinguishable from board. Unpainted, the surface is slightly rough and often shows fine surface crazing. The distinction that matters here is against asbestos insulating board, which is softer and licensable; cement is hard and normally is not.
Modern fibre cement
Since the ban the same products have been made with cellulose and synthetic fibres. The profiles were kept deliberately compatible so that repairs could be made, which means a roof can hold both. Age of installation is the honest starting point, and a sample is the finish.
What to look at and what to avoid
Look at the fixings, the profile, the surface weathering and the building date. Do not break a corner off to look at the edge, do not scrape it, and do not clean it to see it better. Pressure washing an asbestos cement roof is one of the reliable ways to turn an intact surface into a contamination problem.
Questions people ask about what does asbestos sheet look like
Is corrugated sheeting always asbestos?
No. The same profiles are made in modern fibre cement and in steel. The building date narrows it and a sample settles it.
How thick is asbestos cement sheet?
Usually only a few millimetres, which is why it is light, brittle and fragile as a roof covering rather than something that will carry a person.
Can I tell by tapping it?
A dull sound suggests cement rather than metal or plastic. It says nothing about whether the cement contains asbestos.