Q: I want to tile the ceiling of my client’s bathroom, including the shower. How should I detail the setting bed, and how do I keep it from all falling down?

A: Michael Byrne, veteran tile installer and consultant, and moderator of JLC’s ceramic tile online forum, responds: A tiled ceiling can literally be the crowning glory of a shower stall, but there are a few things you should do to ensure a durable, attractive, practical, and safe installation.

One of the most overlooked aspects of tiling a ceiling in a wet environment such as a bathroom or shower is that the ceiling should be sloped or crowned. The unsightly brown spots that you often see on flat tiled ceilings are actually the beginning of stalactites forming as water vapor condenses on the ceiling tiles and leaches minerals out of them. This problem can be eliminated by drying off the tiles each time the shower is used, which is inconvenient at best. But if the ceiling tiles are sloped, most of the surface moisture simply drains to the walls.

The Tile Council of North America (TCNA) says that the ceiling on a fully enclosed steam shower must be sloped a minimum of 2 inches per foot, and I use this as a good rule of thumb for any tiled ceiling in a wet area. The slope can be angled like a shed roof, peaked, reverse-peaked (so moisture flows toward the center of the shower, which is a common configuration in large steam showers that have benches on opposing walls), or—my favorite—arched.


To shed water properly, bathroom ceilings should never be flat. Here the ceiling is arched and a tight grid has been framed to support the tile. Strips of green board form the initial arched surface.
To shed water properly, bathroom ceilings should never be flat. Here the ceiling is arched and a tight grid has been framed to support the tile. Strips of green board form the initial arched surface.

Another important part of tiling a ceiling is providing solid support for the tile. For any of these designs, I begin with framing members spaced 12 inches apart. For an arched ceiling, I make curved joists out of 3/4-inch plywood. Then I block between the arches to create a very strong framing grid. I never recommend applying tile directly to greenboard, but I use strips of greenboard attached to the arched framing as a support base for the mortar setting bed (see photo above). I spread a layer of cold-patch roofing tar over the greenboard strips and then staple a layer of 30-pound felt paper over that.

An alternative to greenboard is two layers of 1/4-inch cement backerboard screwed into the joists. Attach the backerboard one layer at a time, applying thinset mortar between the layers for added strength and stiffness.

When I did the ceiling in the photos, I let the roofing tar create my moisture barrier; for extra protection, sheet-style waterproofing membrane such as Noble Seal TS can be installed between the mortar bed and the support base, or between the framing and the first layer of backerboard.

To waterproof the ceiling, a layer of cold-patch tar is spread over the green board followed by a layer of 30-pound felt paper. Wire mesh is then nailed in over the entire surface.
To waterproof the ceiling, a layer of cold-patch tar is spread over the green board followed by a layer of 30-pound felt paper. Wire mesh is then nailed in over the entire surface.
A layer of mortar is smoothed  onto the wire mesh with a trowel. When the mortar dries, the tile installs over the mortar with thinset.
A layer of mortar is smoothed onto the wire mesh with a trowel. When the mortar dries, the tile installs over the mortar with thinset.

I then attach wire mesh to the ceiling (photo left) and trowel on a layer of mortar for the setting bed, smoothing the curve with a flat trowel as I go (photo right). Finally, I use regular latex-modified thinset and back-butter all ceiling tiles as they go in. Surface tension holds the tiles in place until the mortar cures. When tiling a sloped or curved ceiling, begin at the lowest points and tile toward the highest point. Use spacers as needed to keep the tiles from sliding, which can break the surface tension and cause the tiles to fall.

Photos by Michael Byrne