Backerboard

Backerboard, or tile backerboard, is a building substrate placed behind tile and other surface coverings in walls or floors. It provides a rigid, stable base for tile adhesion and helps protect against substrate movement that can cause cracking. Most backerboards are moisture resistant but not waterproof by themselves; they are used in conjunction with a waterproofing membrane in wet areas such as showers and tub surrounds.

Common types include cement backerboard (cementitious boards with fiberglass mesh) and fiber-cement boards. Foam backerboards (extruded polystyrene or polyiso cores with a cementitious coating) are lighter options used behind tile in some installations. Gypsum-based backerboards exist but are generally not recommended for continuous wet areas; specialized gypsum products may be used behind tile in dry areas. Backerboard thickness varies, with typical wall applications using 1/4 to 1/2 inch (6–12 mm) and thicker options available for floors or heavy loads.

Installation typically involves attaching the backerboard to studs or subfloor with corrosion-resistant screws or nails, keeping fasteners slightly below the surface. Joints between boards are filled with fiberglass mesh tape and thinset, then the surface is prepared for tile with a skim coat of thinset. In wet areas, apply a waterproofing membrane over the backerboard according to product instructions.

Benefits include a stable, non-porous substrate for tile, improved adhesion, and reduced risk of substrate-related cracking. Limitations include the need for proper waterproofing, since backerboard is not inherently waterproof, as well as potential for added weight and the need for appropriate cutting tools and installation care.