A shower wall can be a breeding ground for mold growth on interior wall cavities as pounding water and dense vapor penetrate grout joints between tiles, the mortar thinset and the tile backerboard in your shower surround. Using products designed to withstand moisture and humidity is key to preserving the physical integrity of your shower and in protecting your family from the potential health hazards that mold proliferation can cause.
Backing Products for Tile
Tile placed on a wall must be attached to a flat, well-secured underlayment. In areas where moisture is not an issue, drywall provides a good tile base. In tiled areas subjected to occasional water or moisture, water-resistant gypsum backing board is preferred. Do not use water-resistant gypsum backing board, also called green board because of the color of its face paper, as a base for tile where high humidity is a constant. In these applications, supplemental protection is necessary.
You may use greenboard as backing for shower tile if the shower area is properly ventilated. The Gypsum Association recommends a ventilation rate of at least five air changes per hour. Showers located adjacent to an exterior wall need insulation against condensation on the interior wall surface. Horizontal surfaces within the shower, such as soap dishes and ledges, must slope to direct shower water harmlessly towards the shower drain.
Water-resistant tileboard must be correctly applied to properly-aligned and correctly-spaced framing members. Framing should be spaced at intervals no greater than 24 inches on center. Wherever framing is spaced more than 16 inches on center or the tileboard must support tile that exceeds 5/16 inches in thickness, you must apply blocking between the studs. Framing must be shimmed to provide tight, strong corners which, in turn, will provide a sturdy, true base for tile.
Concrete and fiber cement backerboard, commonly used as an underlayment for floor tile, is also an acceptable underlayment for shower wall tiles. Use galvanized screws or nails to attach the boards to prevent the development of rust. Backerboard sheets should center over the studs with joints staggered. Self-adhering fiberglass tape should cover all joints. An application of thinset mortar, applied over the fiberglass with a taping knife, readies the wall for mudding and tiling.
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