When you lay tiles, the space that you leave between the tiles depends upon the manufacturer's recommendations. This information is included in the paperwork provided with the tiles. Some manufacturers recommend a range of possible gap sizes, from 1/8-inch to 1/4-inch, which allows some flexibility in the appearance of the tile job. These spaces between the tiles are created with tile spacers that separate the tiles as you lay them out in the adhesive.
1/8-Inch and Smaller
When you leave a gap of 1/8-inch or smaller between glass tiles, unsanded grout provides enough support to keep the tiles stable and secure on the surface. Unsanded grout has a smoother texture than sanded grout, which makes it gentle on the surfaces of glass tiles during the application process, and is available in a number of colors that provide you with a variety of color scheme options for the tile job.
Larger than 1/8-Inch
If you install larger glass tiles, the manufacturer may recommend a gap larger than 1/8-inch between tiles. Gaps between glass tiles that are larger than 1/8-inch should be filled with sanded grout. Sanded grout provides a more heavy-duty hold and is less prone to cracking when used in larger spaces than unsanded grout. Since sanded grout has a gritty texture, though, you must take care, while applying it, to prevent scratches on the glass tiles.
Grouting and Drying
Whether you apply sanded or unsanded grout to your glass tiles, you should use the same basic method. Grout can be spread over the glass-tiled surface with a grout float or a putty knife. When applying sanded grout, use gentle strokes and concentrate on getting the grout only in the spaces between the tiles to prevent scratches. With either type of grout, wipe it from the surface of the glass tiles, while it is wet, to prevent the grout from permanently drying on the tiles.