Can You Put Tile Over a Prefabricated Shower?

Rated Underlayments

• There are a few types of underlayments that are rated for use with tile installations, including cement boards, fiber boards, drywall, waterproof drywalls, membrane systems and exterior plywood (which must be coated with waterproofing for use in showers). Plastic is not a rated underlayment for a variety of reasons, and installing tile over it will void any warranties associated with the installation, from the materials to the labor of the craftsman.

Cement Adhesion

• One of the primary reasons you cannot use tile with a prefabricated shower is that traditional thinset mortars won't adhere to plastic due to their cementitious nature. Epoxy thinset can be used, but there are issues beyond adhesion to worry about. Even if you rough up the surface with a sander, thinset mortar will still fail against plastic, leading to tiles popping off the wall.

Nature of Prefabricated Showers

• Movement is always present in prefabricated showers. Since they're constructed out of a single piece of plastic that's poured into a mold, or installed as several molded pieces that are glued together, it's one entire piece of enforced plastic that transfers movement throughout the entire shower. Any weight from humans stepping in or out is carried up the wall, and there is no way to reinforce the wall sufficiently to support tile.

Movement

• The movement that's transferred up the wall from the plastic panels is death to a tile installation. While thinset mortar can soak up some types of movement -- such as from light foot traffic on floors or the expansion and shrinking of the cement in the warm and cool months of the year -- it cannot absorb the movement from a shower. You'll be lucky if your tiles stay on the wall for more than a couple of weeks.