Based on temperature of formation, there are three types of glass tile: cast glass tile, fused glass tile, and low-temperaturecoated glass tile. Each type can be subdivided, based on size, into three subcategories: large format glass tile (typically larger than or equal to 3” x 3”), mosaic glass tile (typically larger than 3/4” x 3/4” and smaller than 3” x 3”), and miniature mosaic glass tile (typically smaller than or equal to 3/4” x 3/4”). Cast, fused, and low-temperature-coated glass tiles are produced in many sizes with wide varieties of opacity ranging from opaque to translucent. All glass tiles have characteristics different from ceramic tiles.

Cast glass tiles are formed in a liquid state at 1600°F or higher. Many cast glass tile surfaces are wavy and slightly textured with inherent folds, bubbles, and creases. These unique intrinsic properties are achieved through the casting process.

Fused glass tiles are typically made from sheet glass units that are altered through heat between 1023°F and 1599°F. During manufacturing, different materials and glazes are fused to the sheet glass units, usually in multiple stages, to create a variety of colors and patterns. Fused glass tile surfaces can be smooth, textured, uniform, or nonuniform.

Low-temperature-coated glass tiles are made from sheet glass units that are altered at temperatures less than 1022°F. Typically, these alterations involve heat-transferred coatings applied to the back of transparent sheet glass units. These coatings can contain wide varieties of colors and patterns.

Although the types of substrates recommended for glass tile installations are similar to ceramic tile installations, extra attention should be given to substrate stability, rigidity, and preparation. Where a substrate is appropriate, glass tile will be listed as an option in the Materials section of the applicable method.

Substrates should be sufficiently flat to allow uniform coverage and avoid excessive mortar thickness. Glass tile should not be installed on single-float mortar bed walls framed with wood or metal; and glass tile should never be bonded directly to wood substrates. For above-ground slabs, reinforced mortar beds may be required, especially for large-format glass tile. Some manufacturers require mortar bed substrates be cured a minimum of 7 days prior to glass tile installation. Glass tile is generally more vulnerable to crack propagation than ceramic tile. For nontranslucent large-format glass tiles, the glass tile manufacturer may recommend the use of ANSI A118.12 crack isolation membranes.

To achieve suitable bond strength for glass tile, setting materials with sufficient adhesion properties are needed. Generally, it is necessary to use high-performing ANSI A118.4 or ISO C2S1 or better mortars to achieve such adhesion. Manufacturers commonly have recommendation lists for such products. Due to the imperviousness of glass tile, setting materials may take longer to cure, particularly when also installed over an impervious substrate.

Some low-temperature-coated glass tiles are not intended for installation with cementitious materials. Cement mortar alkalinity may deteriorate those low-temperature-applied backings and increase the risk of delamination, particularly in wet or humid environments. Follow manufacturer recommendations for bonding low-temperature-coated glass tile products.

Organic adhesives are not typically recommended for use with glass tile but may be needed for certain low-temperature coated glass tiles. Consult tile and adhesive manufacturer.

With translucent glass tiles, setting material color and full coverage are essential; white is commonly recommended. Avoid using setting materials from different production batches and check for bag-to-bag color consistency. To achieve uniform coverage, back-buttering is often employed and the trowel ridges flattened prior to setting translucent glass tiles.

For hollow shaped pieces (v-cap, quarter round, crown caps, etc.), back-butter the tile but do not fill the cavity. Excess setting material can shrink and may cause cracking or ghosting, a slight visible separation of the mortar from the glass tile. Ghosting and cracking may be avoided through proper substrate preparation, mortar selection/mixing, and tile installation technique.

Grout type recommendations vary between glass tile manufacturers based on aesthetics and joint size. While some glass tile manufacturers specify unsanded grout, to prevent scratching, others require sanded grout. Manufacturer recommendations also vary with regard to whether or not the use of epoxy grout is acceptable. Consult glass tile manufacturers for grouting instructions.

Grout joints should be filled uniformly and consistently, as spaces and voids can be visible through translucent glass tile. Because glass tile is impervious, additional setting time may be necessary to allow the grout to firm prior to cleaning.