Grout joint width picks the grout — sanded for wide joints, unsanded for narrow
Joint width decides the grout: ≥1/8″ → sanded (the sand resists cracking in wide joints), under 1/8″ → unsanded (sand won’t pack a thin joint). Glass and cement tile → ALWAYS unsanded, because sand scratches glass.
What this diagram shows
A comparison of two grouted tile joints in cross-section. A wide joint of one eighth inch or more is filled with sanded grout, whose sand aggregate resists shrinkage cracking in wide joints. A narrow joint under one eighth inch is filled with unsanded grout, because sanded grout cannot pack into a thin joint. The rule: joints one eighth inch and wider use sanded grout, joints under one eighth inch use unsanded, and glass or cement tile always uses unsanded grout because the sand in sanded grout permanently scratches a glass tile surface.
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