QUESTIONHow much lippage is acceptable for glass tiles? - what is the standard tolerance for uneven height between 2 tiles in a 1/16" space installation in a glass tile 32"x32"?
ANSWERANSWER - There are no specific standards for lippage for glass tile, although I think it could be reasonable to apply the ANSI A108 standards for ceramic tile to glass tile.
The standard says that grout joints that are less than 1/4" wide cannot have more, lippage between two adjacent tiles, than 1/32" in addition to the inherent allowable warpage in the tile. Some glass tiles are intentionally very irregular and give a somewhat rustic look, and they may have more lippage than a tile that is designed to be more consistent in size.
You indicate that these glass tiles are 32" x 32" which is quite large, and there are additional provisions for tiles that size. The standards say the grout joint width should be at least 3 times the actual variation of the facial dimension of a tile. If the tile is being installed in a running bond pattern and it has any side greater than 15" the grout joint shall be minimum 1/8" wide for rectified tiles (ground to precision sizing) and minimum 3/16" for calibrated tiles (non-rectified). Further it says that tile installed in a running bond tile pattern where one side is greater than 18" the offset cannot be more than 33%.
Thus if the grout joint width is more narrow than recommended, then it may result in excessive lippage. In addition, the substrate that the tile was installed over should have been within standards of no more variation out of plane than 1/8" in 10 feet.