We used what's called; "Latex-Modified Mortar" specifically made for glass tile from Lowes. It works very well. Once it sets up, you grout with your preference of grout color. The Mortar works great it'll easily hold the glass tile sections on a vertical wall.
One word of caution, I got too generous with the trowel and the motar leaked thru the tile cloth mesh and I had to clean out some mortar before I could grout, so don't get too carried away applying the mortar.
Rockwood 2104S, 2014 Ram 2500 Diesel.
USMC 68 -70