What is cement board (backer board)?

Cement board, also called backer board, is a rigid panel composed of Portland cement and embedded fiberglass mesh. It serves as a moisture barrier between tile and the framing behind walls and floors in bathrooms, showers, and kitchen backsplashes.

Unlike drywall, which absorbs water and fails quickly in damp conditions, cement board resists moisture penetration. Greenboard (moisture-resistant drywall) offers limited protection compared to cement board and is not suitable for direct tile backing in shower enclosures or areas with standing water. Cement board is fastened directly to studs or joists and tiled over, creating a stable, waterproof assembly.

Contractors choose cement board for its durability in high-moisture environments. Common thicknesses are 1/4 inch for walls and 1/2 inch for floors. The material is non-combustible and stable enough to support heavy tile loads without flexing. Proper installation includes waterproof membrane over seams and corners, especially in shower areas, to create a complete barrier system that protects the structure beneath from water damage, rot, and mold growth.