Durock® is a brand of cement backer board manufactured by the United States Gypsum Company, which is a subsidiary of USG Corporation founded in 1901. Cement backer board is most often used as a subfloor or wall base when installing ceramic, porcelain or stone tiles. Cement backer board is called by a variety of names such as cement board, backer board or tile underlayment. Additionally, some refer to all cement board as durarock, which is a metamorphosed version of Durock®. It is very similar to the way most people refer to all plasterboard as Sheetrock®, which is actually another one of USG’s popular products.
Durock® is composed of an aggregated Portland cement core which is coated with a glass-fiber mesh on one side. The smooth side is used for adhesive applications while the mesh side is used for thinset mortar or mastic application. Durock® can be scored with a utility knife so it breaks easily for do-it-yourselfers who don't have a saw. When installed, the seams should be scattered. Additionally, the seams must be taped and prefilled with mortar for the best results.
Backer board provides a level and supportive base for glass and ceramic mosaics, tile, stone and brick. Whether using cement board in new construction or remodeling, it may be installed over a wood or steel frame to walls, floors, soffits, partitions, countertops and ceilings. The cement board is fastened with cement screws, self-drilling fasteners or nails.
Durock® cement board comes in two sizes. The 4 inch x 4 inch is 5/16-inch wide and the 3 inch x 5 inch cement board is ½-inch wide. The thinner Durock® offers less support so it may be used for thinner tiles, while the thicker board will be needed for thicker tiles and floors with inadequate support because of the direct pressure applied when people walk on them. The different thicknesses also help maintain even transition areas on the floor.
One of the most common areas to use Durock® is in the bathroom because it is mold and moisture resistant. Cement board is necessary where water may run on the floor, but it is mandatory for tiled showers or tiled areas above a bathtub. Durock® may also be used in pool areas or saunas. It also has applications in the areas around fireplaces and wood burning stoves. The product is noncombustible and it will not swell, soften, decay, delaminate or disintegrate according to the manufacturer.