I need to cut out a shape (rectangular opening) inside a cement board. Was wondering if it can be done with a jigsaw and a special blade once I have pilot holes drilled in each corner.
There is no real experience needed when cutting an opening in cement board. I've seen openings for faucet handles created with nothing more than a well placed hammer strike (one hit each hole!). What ever tool you have available will suffice. I've drilled perforations with a masonry bit for a single shower valve. Oscillating tools with a carbide blade work. The primitive method is to cut the mesh with a utility knife and then force the board to break along the cut line. For a triangle cut not along an edge, mark the outline with a pencil, and drill a 3/8 inch hole at each of the 3 points. With an aggressive saw blade follow the lines to each 3/8 inch hole. If the edges are to jagged smooth with a rasp or a whet stone.
I've cut out pieces in the middle of cement boards starting with a well placed whole saw drill bit for an opening, and following up that area with a sawzall shortblade for the actual shape. Grab a spray bottle with water to control the dust. It's a bit primitive but works well.. Good luck!
Yes, it can be done... Personally, I would avoid high speed cutting tools, and simply use a drywall knife. It works very well. Leave one of the 4 edges uncut to simply score with a utility knife (as usual) to snap it. I've done this on several cement boards, and it works much better (imho) and without any dust.