Cutting Cement Board Video
You can cut cement backer board with a circular saw, with an abrasive or diamond blade. But that is dusty and hard on the saw. It can be cut similar to drywall with a knife. Instead of a razor knife, the preferred tool is a carbide-tipped knife.
To make your cuts, mark the cement board on the smooth side and scribe your cut line. Take the cutting tool and scrape along the line several times. Once the scoring is complete, lift the backer board and apply pressure on the back side behind the scoring. After snapping the cut line, use the cutting tool to cut along the cut several times. This will finish cutting through the cement backer board. It’s just that easy.