Considerations When Installing Glass and Mosaic Tile

For thousands of years ceramic and other hard tiles have gone through countless style changes, and today, thanks to technological innovations, tiles are no longer just for royalty, churches, mosques or the super-rich, but rather for almost every budget. In addition to beauty, one of the main reasons for their long-standing popularity, tiles have the lowest lifecycle costs of any finishing material. But to enjoy both benefits – beauty and low lifecycle cost – tiles must be installed properly. Even the humblest tiles deserve a proper installation, but when installing especially beautiful tiles, installers need to be especially careful.

Fifty years ago in the U.S., tile used to mean low-fired, high-absorption, gypsum-bodied tiles for walls, and semi-vitreous tiles for floors. Porcelain tiles were also used on wet area floors. Their size was limited to 1x1, 1x2, or at most 2x2 inches, and these small tiles were mounted on sheets for easier installation.

Today, low-fired wall tiles and semi-vitreous floor tiles are still being used, but large-format porcelain tiles have all but replaced semi-vitreous floor tiles. Small-size mounted porcelain tiles have been around for close to a hundred years and there are no indications they will go out of style unless installers stop using them to conform to sloped surfaces found on shower floors or other sloped floor applications.

In previous editions of FCI, I have covered the installation of glass tile (FCI May/June 2012) and mosaic tile (FCI December 2012), but as the popularity of these two types of tile increases, they deserve a second look.

Glass tile. Although the perception suggests that it is a newcomer to the tile industry, glass has a very long history. Bits of glass have been incorporated into mosaic work for about 4,500 years, while the first glass tiles first appear around the third century B.C. Paper-mounted sheets of uniform sized colored glass mosaic appeared about a hundred years ago, but it was not until recently – about 20 years ago – that advances in technology allowed the manufacture of glass tiles in the range of 4 to 6 inches.

Today, glass tile larger than 12 inches on edge are being sold, and there is no reason why, as manufacturing technologies advance, even larger glass tiles can’t be made. Glass tiles are available in a bewildering array of styles, colors, and composition, with some glass tiles made of 100% recycled materials – an important consideration for many consumers. Glass tiles usually have a smooth surface, but the surface of some is textured.

Color is a major consideration with glass tile. The glass body of the tile may be colored, or the color may be applied to the back of the tile. Back coloring can be done with a paint-type coating, or it can be a thin layer of colored glass fused to the tile body. Some glass tiles are… well, they are as clear as glass. All four types have critical adhesion requirements that should be specified by the manufacturer.

Depending on the area to be tiled, some glass tiles can be installed with organic adhesives. While latex or epoxy thinset mortars provide a more durable installation, installers should always follow a manufacturer’s instructions. In addition to following adhesive specifications, another key installation element is how those adhesives are applied since many glass tiles are semi- or completely transparent. Adhesive ridges should never show-through as this would mar the appearance of the installation. As well, voids within the adhesive bed should be totally eliminated because, in wet areas, voids can collect water, which can harbor mold and show through transparent glass tiles. There should not be any voids in the grout for the same reasons.

Grey thinset mortar will dull the appearance of transparent glass tiles, while white adhesives brighten them. A designer can be creative with clear glass tiles by specifying a colored thinset mortar with a color-matched grout. I frequently use colored thinset to deepen and enhance colored transparent glass tiles, and finish the installation with a matching grout. To make colored thinset mortar, I select a regular, non-modified grout, use it as a powder base, mix it with LATICRETE 4237 to create a latex-modified colored thinset, and mix the same grout powder with LATICRETE 3701 to make latex-modified grout. There are other products out there, of course, but these are the ones I use.

Mosaic tile. The mosaic arts begin about 4,000 years ago, and surviving ancient mosaic compositions contain a wealth of human history that, unlike ancient wood, cloth, papyrus or paper artifacts, can easily last tens of thousands of years or more. For most of its history, mosaic art has been decorative, functional and expensive. Very expensive. Mosaic compositions were made of pebbles, shell fragments, polished stones, ceramic bits and glass. The backs of some transparent glass mosaic tiles were gold-leafed and then covered with a thin protective layer of glass.

Many surviving mosaics from centuries ago are truly spectacular works of art. By the 1920s, though, the mosaic arts had been mostly replaced with functional, utilitarian installations. During the past 20 years or so, though, decorative mosaics have made a robust and splashy comeback. And just like the mosaics of old, today’s offerings are made from pebbles, shell fragments, polished stones, ceramic bits and glass – and as you may already have guessed – gold-leafed glass.

This article will not cover purely artistic, one-of-a-kind mosaics but rather the off-the-shelf variety available at most tile showrooms which I will divide into two categories: opaque and transparent (or translucent). Off-the-shelf may sound like another word for “ordinary,” but a walk through a tile showroom displaying sheets of mosaic tile will show that modern mosaics can be bright, colorful, highly ornate, textured, unusual, stylish, fun and practical.

Depending on the type of materials arranged on its mounting and a manufacturer’s recommendations, a sheet of mosaic may be used on floors, walls, countertops and exteriors with only a few restrictions. One of these is surface hardness. Some mosaic sheets made of soft materials or fragile glass should only be used on floors where traffic is limited to soft footwear (slippers) or bare feet.

Another limitation involves floor loading. Bare feet standing on a sloped mosaic shower floor do not exert much of a load so even tiny mosaic bits can be used. On heavy-duty applications that have to support hard or soft wheeled carts, floor cleaning machines, or high-heel spike shoes, mosaic tiles may not be able to stand up to this kind of loading. One more limitation involves exposure: what materials are going to be spilled on, slopped on, or ground or mashed into the surface of a mosaic installation?

Under these conditions, the relatively large amount of grouted surface can create cleaning and maintenance nightmares so larger tiles should be used. If you want to have mosaic tiles in your kitchen, install them on the countertop’s backsplash where exposure to materials that stain or are difficult to clean off is limited. If only mosaics can be used under harsh exposure applications, use an epoxy grout to make cleaning and maintenance easier.

Mosaic bits are mounted in a variety of ways. Traditional opaque glass mosaic squares are usually face-mounted with a sheet of paper attached to the bits with a water-soluble glue. After the tiles are installed, the sheets are moistened with water, and when the glue dissolves, the paper sheet is easily peeled off.

Perforated paper sheets can be mounted on the backs of mosaic sheets, but I don’t recommend this type of mounting in wet areas or floors. Mold likes to dine on paper, and the perforations can significantly reduce that amount of adhesive that grips the tile. A back mounting material that does not reduce the adhesive footprint or support mold colonies is made from hot strands of plastic drizzled onto the backs of the mosaic bits: this type of backing requires no glue.

Plastic netting is also used, but if the netting is attached with a water-soluble glue, and the assembled sheet is installed in a wet area, moisture can re-emulsify the glue and ruin the adhesive bond, thus eroding support for the mosaic bits and, on a floor application, severely reducing the installation’s load-carrying strength.

When installing transparent or translucent mosaic sheets, follow the same adhesive and grout guidelines listed above for glass tiles with one additional and relatively simple technique that should also be used when installing opaque mosaic sheets. 

That technique is to flatten the adhesive ridges that are formed when a notched trowel is used to spread the adhesive. These ridges can ooze up between the open joints of mosaic bits and create a cleaning nightmare for the installer. To gauge a consistent amount of adhesive, a notched trowel has to be used, but to avoid the ooze, after the adhesive is spread with a notched trowel, use the trowel’s smooth edge to gently flatten the ridges. This way, the mosaic sheet can be pressed into the layer of adhesive without any high ridges to clog the grout joints.

Mosaic tile sheets require careful attention to details, but the extra work involved is minimal, and if done right, a mosaic installation can provide a lifetime of easily maintained service.