HardieBacker board comes in 1/4-inch and 1/2-inch thicknesses. The 1/4-inch cement board is typically used for floors, while the 1/2-inch product is used on walls. Containing about 90 percent cement and sand, the panels can form a subsurface for tile installations. Although such panels may seem difficult to cut, there is a special carbide-tipped scoring knife for cutting the panels. The panel is scored several times and can be snapped apart in a method similar to cutting drywall.
Lay the panel flat onto a work surface.
Measure the desired dimension for the cut you need to make on the panel using a tape measure. Mark the measurement with a pencil in two spots -- one toward the top of the panel and one further down.
Connect the measurement points using a straightedge to mark the cut line onto the panel.
Hold the straightedge along the pencil line. Drag the knife from the top of the panel down along the line using the straightedge as a guide to score the panel several times. Four to five passes should do the job.
Hold one side of the scored line flat against the work surface and pull up on the other side of the panel to snap the scored line apart. Remove the scrap panel and set it aside. Make any further cuts to the panel in the same manner.