Glass tiles are gaining in popularity, with more types and styles available than ever before. Since glass is unlike any other tile product on the market, it does require special care and setting materials when being installed. Failure to use the right type of setting material may harm the installation.
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Color of Mortar
Most types of glass tile are translucent or transparent, meaning that they can be seen through. Whether the glass is perfectly clear or whether it has a color to it, if it can be seen through, the color of the mortar will affect the installation. For this reason, only white mortar is used to install glass tiles. The white color of the mortar will help the glass show its colors without dulling or darkening them.
Flexibility of the Mortar
Glass has no ability to bend, flex, or absorb impact or motion. For this reason, the mortar behind it must absorb some of the stress of the house settling. Latex additive thinsets, such as Tec's Super Flex, are specially made to handle the fragile glass tiles. The mortar will bond with the glass and the substrate but can flex slightly if required, absorbing the stress that could crack the glass.
Thickness of the Mortar
Glass tiles cannot absorb moisture. For this reason, only thinset mortars can be used behind them. If the mortar is too thick, it will be unable to dry out properly from behind the nonporous glass tiles. Moisture must escape from around the glass tiles, through the grout joints or into the backing behind the adhesive. If the mortar is too thick or heavy, there will be too much moisture to escape through these avenues, and shadows could appear behind the glass, or the tiles' installation could fail.
Use of the Mortar
While all mortar is "keyed" or raked with the ridges of the trowel when it is spread on the substrate, mortar used with glass tiles must be keyed first and then smoothed out before installation. The keying is important to achieve the right thickness of mortar on the wall. Since glass is transparent or translucent, any ridges left behind by the trowel would be visible as shadows through the tiles. This will affect the visual appearance of the tiles; therefore, the mortar should be smoothed out before the tiles are pressed into it.
Additions to the Mortar
In addition to white latex additive thinset mortars, other setting materials that may help the installation of glass tiles are available. Crack-reducing membranes can be painted onto unstable surfaces to help absorb additional stress before the mortar is applied. Additionally, latex additive caulks should be used in all corners or 90-degree angles of glass tile installations to help absorb stress and movement and prevent cracks in the tiles.