Fibro cement sheet (the stuff that replaced asbestos) seems to be tough. I needed to make some ventilation holes, and got out my hole saw (intended for wood). It made two 67 mm holes but the third took ages. The teeth were blunt as a budgerigar's bum afterwards. So I bought another hole saw, the cheapest I could find, but that only did one hole and the teeth were gone. So I wonder: are there hole saws made for masonry? I have not seen such item at local hardware emporium.
P.S. I did use a dust mask and ensure others were away while attacking this fibro shit.