What kind of cirrcular saw blade do I use to cut cement board?
Use a board saw - it's basically the same as working with plasterboard/sheetrock
a cement board blade works well
you can use a diamond blade to cut cement boards, gets pretty dusty though but can be pretty helpful when there are a lot of obstructions to cut around
Circular saws aren't the best idea actually. The cement is harder than metal, so you'll ruin almost any kind of saw! My best idea is to drill holes close together in a line along the cut you want to make. Then get a table of some kind and slam it down on the side so it breaks. The holes you drilled will ensure the crack stays along that line since that line is the weakest part of the cement. Or maybe you can get a big chisel and a sledgehammer and hammer at the chisel in the line. But it's not going to work as well, I can guarantee you.
You can score and snap straight cuts. But this will not work for inside corner cuts. Or you can purchase a blade specifically for cement board....they are pricey. The option is an inexpensive carbide tipped blade.....about $8-12 and after a dozen or so cuts throw the blade away. You will create alot of dust using the circular saw. Another option for smaller projects is using a jig saw with a bi-metal blade....creates alot less dust.
