The answer is straight forward but even before I knew what it was the people at the store couldn’t always tell me. Sanded grout is much more typical and is used in any joints greater than 1/8 inch. The sand provides aggregate as the grout consists of dye, sand, and Portland cement. Unsanded grout, as the name clearly states, has no sand and is used for joints less than 1/8″. The sand grains make it difficult to pack sanded grout into small gaps.
OK, quiz. I used two kinds of grout in the tiles below.
1) What kinds of grout?
2) Where did I use them?
The mosaics on the left used unsanded and the subway tile on the right with 1/4″ gaps used sanded grout.
Do NOT use unsanded grout in floor tile, so do not use mosaics with small gaps on floors because the grout will crack and break.
Buy grout with MATCHING siliconized caulk. Spend the extra money on the matching caulk and apply it to your inside corners.
Most importantly: Read the instructions on the box