1/2 inch thick sheets of hard material composed of cement and fiberglass, which is used as a backing for ceramic tile or as an underlayment in showers, wherever a moisture barrier is needed, because it is waterproof. Cement board is installed much like drywall; the 3 x 5 foot sheets are cut to size and fastened using drywall screws. Joints are sealed with drywall joint tape and thinset mortar or the tile adhesive. Wonder Board and Durock are the two most well-known brands, with wonder board being used generically. Also called "glass mesh mortar unit."

A cement board is a concrete board that can be used like any tile. It can be placed on any subsurface such as bathroom and kitchen backsplashes, as well as buildings and furniture. Cement board is useful because it resists shifting, and is impervious to water and scratching.