Glass Mosaic Tile Installation For a Steamer Shower

I’ve always enjoyed installing residential tile. There’s something about thinking creatively and making an artistic statement that appeals to me with the challenge. To express a customer’s design vision calls for good communication skills and at least some intuition. Making a customer happy and feeling comfortable in their home environment makes me happy, too. Nothing can compare to the satisfaction of knowing a job has been well done, in seeing a beautiful and properly installed tile job. And, indeed, a glass mosaic tile installation can look fantastic. This glass mosaic installation sure was a challenge in it’s complexity.

A short while ago Debbie and Rich asked me to finish a bathroom that would include tiling a steamer/shower surround with glass mosaic tile, for shower pan, walls, and ceiling. They chose a transparent glass mosaic called Tesserra red #777, non-iridescent, by Oceanside Glasstile of Long Beach, Calif. I believe they wanted to see as well as feel the red hot heat of a steam bath. The glass mosaic tiles were of the same red hue, but randomly varied in saturation: some glass tiles were darker or lighter than others.

Each one inch square handmade mosaic glass tile was a quarter inch thick with a finished face surface that was seemingly chipped, crazed, or irregular, not smooth. The tiles came in sheets twelve inches square, face glued to brown backing paper with a water soluble adhesive similar to that used for wallpaper. The tiles reminded me of chipped ice cubes, with sides tapered away from the face and a flat back slightly textured from molds. Most tiles were fairly square, some were slightly trapezoidal in shape, as the molten glass poured into the molds overflowed a sixteenth inch to form a sheet that was broken apart after cooling.

The bathroom had been framed in and sheetrocked walls and ceiling before my involvement, with green board placed in the steamer/shower surround area. I wanted to jump right in, assuming I could apply a builder’s felt paper moisture barrier over the greenboard, then install cementitious backerboard and parge it with a waterproofing membrane to contain steam. But, being a relative beginner to any mosaic tile installations, it was a good thing that I had some uncertainty, so I decided to talk first to Oceanside’s technical support experts.

Technical support insisted that I remove the greenboard from the steamer/shower surround. Originally developed as a substrate for directly applying tile, greenboard has now become unacceptable for any bathroom use according to building code. Also, there was a chance, however slight, that steam moisture could permeate the waterproofing membrane and eventually dampen any sheetrock or greenboard, causing deterioration and mold buildup where it could never dry out. More recently developed cementitious backerboard, code approved, performs far better for tile, especially in a wet environment.

Then, a key point to this entire installation, technical support strongly advised me not to apply a waterproofing membrane directly behind any transparent tile. Water would certainly settle behind the tile, especially where steam would force it, causing a splotchy look where some tile would areas appear darker than other areas. Untreated backerboard would allow water to diffuse away.

Finally, expansion joints are essential for glass tile installations, as well as most other tiles, especially in a steamer environment where temperature swings are most pronounced. Otherwise, glass tiles, being brittle, could crack or pop off under shear pressure. I was advised to install expansion joints at the inside corners of walls and ceiling, as this steamer/shower surround measured 4’6″ wide, 7’6″ high, and 3’6″ deep. Of course, the steamer/shower surround area 2×4 walls and ceiling were insulated with R-13 fiberglass batts.

With any steamer/shower, it is advisable to slope the tiled ceiling for water runoff to reduce the chance of steam condensation causing dripping. I reframed the flat ceiling to provide a slope of one inch per foot, this being a judgment call on my part, while the Tile Council of North America recommends a slope of two inches per foot (SR614-05).

After removing greenboard in the steamer/shower surround area walls and ceiling, I installed builder’s felt paper over wall studs and ceiling joists, and lapped it over the shower pan vinyl membrane as a final barrier to water penetration. I then installed 1/2″ cdx plywood, which does have some exterior water exposure rating, unlike greenboard. The plywood had the added benefit of stiffening surround walls and ceiling, creating a stable base for the glass mosaic tile. I stopped the plywood at the built-in seat level 16″ above the shower pan, because I was concerned about water otherwise wicking up through the plywood from the shower pan mortarbed. Below seat level I installed 1/4″ backerboard over the shower pan vinyl membrane and then applied hydraulic cement parging to straighten backerboard bulges caused by vinyl membrane folds and to bring the backerboard into plane with the 1/2″ plywood.

I taped and mudded all plywood and backerboard joints with white alkaline resistant fiberglass mesh tape and thinset. Thinset is not impervious to water, of course. Then I applied two thin coats of Mapei’s trowel-on waterproofing membrane system consisting of Mapelastic #315 powder mixed with undiluted Mapelastic #315 liquid. The powder is reinforced with fiberglass fibers and the liquid is an acrylic latex admixture. Be sure to wear old clothing when using this product, because at the consistency of thin pancake batter, the mix may get all over you, especially when working overhead. When set, the waterproofing membrane remains surprisingly flexible and adheres very strongly to anything. All inside plywood corners were taped, mudded, and waterproofed.

Over the waterproofed plywood and backerboard, I installed 1/2″ backerboard, and I again taped and mudded all joints, being careful to stay away from inside corners. In the backerboard corner expansion joints, I installed 1/4″ closed cell polyurethane backer rod, which is water resistant. I caulked over the backer rod with grey Latisil NS polyurethane flexible joint filler/sealant.

After this preparation, I was ready to tile. I was very concerned about the one inch square mosaic layout, trying to eliminate glass cuts and to balance the field width and height. I procured a pair of glass mosaic tile carbide nippers (available from stained glass supply shops or through the tile supplier), which cut the glass with a chiseling action. The tiles may also be cut by a wet tile saw with a continuous, smooth-rim diamond blade, but I preferred to use a hand-held 4″ dry grinder with diamond wheel to trim and square nipper cuts. The glass acted in a fashion similar to chiseling ice – I could never be certain of an initial square cut, but with some practice, the nippers worked quite well. As it turned out, the layout was fairly easy to adjust with the approximate 1/8″ to 1/16″ spacing of the somewhat irregular tiles. I tried most of all to use more than a half tile. Where cut for layout, it was best to cut the tiles a bit more than it seemed necessary.

I started tiling with the shower pan where I could lap over layout cuts at the perimeter with full wall tiles. Installing a square drain cover helped to make tile cuts easier and complemented the square tile theme. I used Mapei Kerabond #102 white dry-set mortar with undiluted Keralastic #310 liquid acrylic latex admixture to enhance bond and flexural strength. I greatly appreciated it’s long open time for this challenging installation. Using the flat side of a trowel, I applied the thinset and then raked it with a 3/16″x1/4″ V-notched trowel to establish the proper depth of the setting bed. I then used the flat side of the trowel again to flatten notch lines and reduce the possibility of air pockets or voids, resulting in a consistent setting bed 1/8″ thick.

The shower pan, seat, walls, and ceiling tile mosaic sheets were then applied to the setting bed with brown face paper outward, using light even pressure to establish setting bed contact and eliminate voids. Then, to achieve a uniform finish surface, a 3/4″ plywood beating block was lightly tapped with a hammer. I worked quickly applying subsequent sheets with grout joints aligned to avoid skinning of the setting bed and to unify the overall tile surface with the beating block. After 15-20 minutes of setting time, I lightly misted the brown backing paper with a household spray bottle several times, patting with a sponge, using a mixture of water and a small amount of DIF wallpaper remover. After the water absorbed into the paper, the glue released from the paper, allowing the paper to be carefully and slowly peeled away to the side without lifting tiles out. Timing of paper removal was critical not to pull tiles out while at the same time allowing for tiles spacing adjustments in the setting bed’s semi-fresh/flexible state. Particular attention was paid before final set to make grout joints adjustments appear random between individual tiles and adjacent paper sheets to eliminate the sheet pattern. Some individual tiles might sag over time – I would eventually remove them, scrape out the thinset behind, then reattach with some new thinset. I even used some plastic tile spacer wedges where necessary.

Some thinset would ooze into and fill adjoining grout joints, but the setting bed was allowed to cure overnight. Then, taking a putty knife, excess thinset could be scraped out from grout joints when still relatively soft, while not disturbing the tiles. After more curing time, I could then remove residual paper and glue by wiping clean with a damp sponge. I waited for several more days before grouting to be sure the thinset had cured.

But before grouting, I filled corner expansion joints with a color matching sanded caulk to be sure grout did not fill the joints. I was amazed at the holding power of the thinset, as during the application of grout, I really had to force it into tile joints. I used a Mapei Keracolor S sanded pearl grey grout. Of course, glass tile is impervious to moisture, so the grout will take a bit longer to set than otherwise.

After cleaning and sealing the grout, I was able to stand back and feel satisfied knowing I rose to the challenge and accomplished something out of the ordinary. Hopefully Debbie and Rich are happy and able to enjoy many relaxing steam baths.