Why smooth out those ridges?
When installing glass tile, especially transparent glass tile, there is one "behind the scenes" step you or your tile installer must take. When applying adhesive to a substrate in preparation for installing the glass tile sheets one uses a notched trowel to ensure the proper amount of adhesive is applied. It is important that you flip the trowel to the smooth edge and proceed to smooth out the ridges caused by the notched edge.
There are a couple of reasons for doing this, one is to ensure that there is 100% coverage and adhesion of the tile to the substrate. The other reason is to eliminate those perfect little pathways that grout just loves to find its way into and travel back behind your tile. Imagine purchasing that gorgeous glass tile and then choosing that beautiful colored grout only to end up with polka-dots or streaks of color behind the tile. It is a must to read the manufacturers setting instructions and setting material recommendations so that you are well prepared for what to expect with your glass tile installation.