A. One of the primary criteria when choosing adhesives for glass tile is the issue of trapped moisture. The impermeability of glass tile often results in trapped moisture after a glass tile installation. This can lead to problems down the line with your substrate, when mold growth becomes an issue which can affect the color of the glass tile, among other issues. Sand-based thin set will limit this problem, as opposed to mastic. When in doubt, seek the advice of local retailers who sell adhesives for tile. Read the instructions of all of the products you decide on, and always follow instructions on the packaging as carefully as you can.