Because the cut is made by abrasion rather than by severing fibres, and fewer teeth generate less heat and less dust. Four to eight PCD teeth on a large blade is normal and correct. A high-tooth-count blade in fibre cement produces more dust, more heat and no better finish.

Polycrystalline diamond, brazed to the tooth in place of tungsten carbide. Fibre cement is highly abrasive because of its silica content, and carbide teeth round off within a sheet or two. PCD lasts many times longer, which is what makes cutting the material economic at all.

Seriously so, and it is the part of the job most often underestimated. Cutting fibre cement releases respirable crystalline silica, which causes silicosis and is a recognised human carcinogen, and dry cutting without extraction produces airborne concentrations well above workplace exposure limits within minutes. It is a health control requirement enforced by regulation in most jurisdictions, not a housekeeping preference, and it applies to everyone nearby as well as to the operator.

On-tool extraction with a suitable class of vacuum is the primary control. Scoring and snapping, or fibre cement shears, produce almost no dust and are preferable where the cut allows. Respiratory protection is required where extraction cannot bring exposure under control, not as an alternative to it.

Other abrasive specialty boards - cement particle board, mineral-loaded panels and some composite decking - where carbide would blunt equally fast. The common factor is an abrasive filler rather than the board being hard, which is what wears the tip rather than resisting the cut.