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Wonderboard® is a backing board made from small pieces of cement pressed between two sheets of glass mesh. The most common use for Wonderboard® is as an underlayment when installing tile. It is particularly well suited for installing under tile on bathroom floors and walls. Though it is not water repellent, because it is made of cement, any moisture that reaches it will not degrade the material or sink into the sub floor. Custom Building Products, the manufacturer of Wonderboard®, further reduces the problems associated with moisture by treating the product with their trademarked MoldGard® technology.
The most common application for Wonderboard® is under tile floors and walls in bathrooms, but it is also used under tile counter tops as well as for outside decking. Wonderboard® is available in one-quarter (0.6 cm) and one-half inch (1.3 cm) thicknesses. It is 36 inches (91.4 cm) by 40 inches (101.6 cm). It is very heavy, and can be difficult to maneuver in the tight spaces of a bathroom. For installing over the sub floor, choose the heavier one-half inch thickness. For counter top installation, the lighter weight one-quarter inch thickness is a better choice.
Wonderboard® is available in home improvement stores, as well as stores that sell flooring and tiling supplies. Another option is Hardibacker®, a backer board manufactured by James Hardie International. Hardibacker® is one-quarter inch thick, and, unlike Wonderboard®, is available in different dimensions. It is available in 3 by 5 foot pieces (0.9 meters by 1.5 meters) as well as 4 by 8 foot (1.2 meters by 2.4 meters). Another difference between Hardibacker® and Wonderboard® is that Hardibacker® does not contain any mesh, only a cement compound. Some people find the Hardibacker® easier to cut because of the lack of mesh.
Backing board is an improvement over the older method of laying tile. In the past, it was necessary to apply the mortar used to lay tile very thickly, to protect the sub floor from moisture. The thick application of mortar, using a trowel, made it difficult to keep the floor level. Backing board has eliminated the need to apply a thick layer of mortar, or mud, when laying tile.