Cementitious Backerboard

Cementitious backerboard is used in both interior and exterior applications and is intended to withstand prolonged exposure to moisture. It is used as a base for tiling applications, countertops, and flooring. It typically consists of a lightweight concrete core wrapped in a fiberglass mesh for reinforcement. The core is composed of Portland cement and generally contains various admixes and aggregates. One lightweight aggregate found to be common in this review was expanded polystyrene (EPS). EPS resin can be purchased with or without a flame retardant. In addition, EPS recycled from sources requiring a flame retardant may be used as an aggregate, so it is possible that some backerboard may contain a trace amounts of flame retardant. Cementitious backerboard has a smooth side for mastic applications and a rough side intended for mortar applications. For wall and ceiling applications the backerboard can be applied directly to wall studs or joists. Flooring and countertop applications require it to be applied over an exterior-grade plywood base. A water-proof membrane may be added between the plywood and the cement backerboard or placed on top of the backerboard. A thinset or mastic is applied on top of this, followed by the tile, grout, and any required tile and grout sealers. Each of these materials may introduce additional hazards not considered by this Common Product. Some manufacturers offer backerboard composed of other materials such as gypsum (without cement/concrete) or polyisocyanurate. These materials are beyond the scope of this Common Product.

The addition of water to concrete causes it to cure, or harden, as the water becomes part of its chemical structure. Manufacturer documentation that breaks out the content of the Portland cement in backerboard generally describes it as the chemical structure would appear prior to curing. Because the composition of concrete is highly variable and requires several reactions to form cement this Common Product also breaks out the content of Portland cement and concrete prior to curing. The typical reaction products are included in the All Contents tab, but the weight percent is not calculated.