Q: I need to cut a piece of cement board into a 30-inch circle. What’s the best way to cut this material?
A: You can cut cement backer board with a circular saw or grinder equipped with an abrasive or diamond blade. A reciprocating saw with an abrasive blade will also do the trick, and so will a backerboard scoring knife, which works like a standard razor knife but with a carbide cutting edge. But for circular cuts, a jigsaw equipped with a carbide blade will probably give you the best control of the cut. The carbide blade has no teeth. Instead, it has a rough coating of tungsten carbide, which is extremely hard. Cutting cement board with a power tool is always dusty, so be sure to wear a dust mask and eye protection.