Since glass is impervious, it requires good mortar mixing and mortar spreading techniques as well as consistent and accurate tile placement. Additionally, some installers have had bad experiences with glass tiles losing bond, generally because they did not use quality liquid latex fortified Portland cement mortar. Impervious tiles like glass require a thin-set mortar with tenacious bond strength. Simple dry-set mortars and most low-end, multi-purpose thin-set mortars do not have the bond strength to ensure a good “grip” to the glass surface. Also, most of the glass mosaic tile made in the past was paper-face mounted. Working with paper-faced tiles requires more skill and accuracy than other type of mosaic tile applications where the tile is generally back dot-mounted or rear mesh-mounted. Most installers have had bad experiences with these types of applications and therefore, shied away from installations similar to these.
For areas where water damage can occur to adjacent or spaces below tile application, use a waterproofing membrane below the tile installation. Consult with the installation materials’ manufacturer to specify a compatible waterproofing membrane system relative to the buildings substrate.
There are several basic methods for installing glass mosaics:
One Step Method: thin-set and grout in one step. If glass mosaics are face-mounted, installers may use this technique. Thin-set mortar should be spread on the substrate with a 3/16” square notch trowel and then additional thin-set mortar is combed onto the backs of the tile sheets, in effect, filling the grout joints with the thin-set mortar. Using a liquid latex thin-set mortar designed for this purpose, contractors should then mix in a sanded grout and use this combination of material as a “colored” thin-set mortar. Tile sheets should be placed into the freshly spread thin-set mortar spread onto the surface and tapped into place with a beating block or rubber grout float. The contractor will then have installed and grouted the tiles in one application. Once tiles have reached an initial set, paper facing should be peeled off. After tiles are set firm, the same “colored” mortar should be used to touch up grout joints where the sheets meet and for any other pinholes, imperfections, etc.
Conventional Two-Step Method: For rear mesh-mounted or paper-face mounted tile, spread the thin-set mortar (generally white in color) using a 3/16” square notch trowel, onto the substrate. Then, carefully set sheets into place and tap with a beating block or rubber grout float. Once the tiles are set firmly in place and paper is peeled off, contractors then can grout all tiles in the normal fashion.
Techniques for installing glass tiles (not mosaics):
Use high-quality liquid latex fortified thin-set mortar. If installing for walls, start from the bottom up – use a supporting ledger board fastened to the wall, in order to support the weight of the installation. Spread the thin-set mortar, using a notch trowel to ensure maximum coverage. Next, knock down the trowel ridges to ensure a continuous coating of thin-set mortar. Tiles should also be back-toweled with additional thin-set mortar to ensuring the mortar’s trowel lines do not show through the glass tiles.
The tiles then should be tapped into place, with either a rubber grout float or a rubber mallet. For larger format glass tiles, layout can make the difference in the final appearance. Spread out the work to visualize the finished job. This is done so that cuts ultimately are minimized. The more full tiles one sees, the better the installation appears.
For best overall performance, and to get a grout joint as dense and easy to clean as the glass itself, I recommend using an epoxy grout. NOTE: Epoxy grout can only be used in the conventional two-step method of tile installation. Generally, epoxy grout is best for wet area applications.
Installers can also use a non-sanded or sanded grout depending on the grout joint texture desired. The non-sanded grouts will have a smoother texture, while the sanded grouts can look a little more rustic. Also, note that most sanded grouts will achieve higher strengths than non-sanded grouts. These are some general guidelines that can be used to install glass tile. However, since there are so many types of glass tiles available in the market, follow the installation instructions of the specific glass tile manufacturer concerning technique, surface preparation, membrane use and placement, adhesive mortar type, grout type and movement joint design and placement.