WonderBoard is a concrete backerboard made by Custom Building Products. The company also produces WonderBoard Lite, which it says is 20 percent lighter in weight. Unlike drywall, backerboard does not contain gypsum. Instead, the product has portland cement and other aggregates, which makes WonderBoard excellent for use in wet areas, such as bathrooms. Backerboard also offers a smooth, level surface for tile and stone applications.
Although it has a concrete-based core, WonderBoard cuts much like drywall. Use a utility knife to score the face, then snap along the score line with WonderBoard positioned on a straightedge, such as the edge of a worktable. Once the waste piece separates, free it by slicing through the mesh backing. Cutouts for fixtures and electrical boxes require the use of carbide-tipped blades or masonry bits, which drive through the concrete material and last longer than steel tools.
The water-resistant properties of WonderBoard help protect underlying framing studs in walls. It's still a good practice to cover the studs in sheets of polyethylene plastic as a vapor barrier, however, before attaching any type of backerboard. On floors or counters, a plywood substrate with 1/8-inch expansion gaps provides the base necessary for WonderBoard. The total thickness of the plywood substrate and WonderBoard together must be at least 1 inch. There is no need to remove flooring materials such as tile, vinyl or linoleum as WonderBoard installs directly on top of them. Likewise, laminate does not need to be removed from countertops before installing WonderBoard.
For either floors or counters, trowel a bed of thinset mortar onto the substrate and notch it with the edge of the trowel. Because flooring is subject to heavy foot traffic, fasten WonderBoard with either 1 1/4-inch cement backerboard screws, or 1 1/2-inch galvanized roofing nails. Space the nails or screws about 6 to 8 inches apart. Wall applications do not need thinset mortar, so screws alone are sufficient for attaching WonderBoard. Stagger the seams between WonderBoard sheets for floor and wall installations. This eliminates a continuous gap along the surface, which can weaken the installation. Leave a 1/8-inch expansion gap between WonderBoard sheets.
Dealing with Seams
Fill in the seams between WonderBoard sheets with thinset mortar. When sheets meet in a horizontal line, add some fiberglass mesh tape and another layer of thinset. Keep the mortar as smooth as possible by feathering it out away from the seam. Once the thinset has dried completely, the WonderBoard installation is complete, and the surface is ready for tiles or other treatment as desired.