When laying tile, you've got two materials that hold the thing together: mortar and grout. Mortar is the "bed" for the tile, and it comprises most of the tilework's structural stability.
Grout--which fills in between the tiles--adds a smidgen of stability and it prevents debris from settling between the tiles.
This background will help you understand why you may want to use sanded tile grout or non-sanded tile grout.
Sanded Tile Grout
- For general use tiling. Sanded grout is your default choice.
- For grout lines 1/8" - 1/2".
- For tile surfaces where the possibility of scratching from the sand content in the tile grout will not be a problem.
- When cost is more of an issue. Sanded tile grout is cheaper than non sanded tile grout.
Non Sanded Tile Grout
- For grout lines 1/8" or less. Sanded grout will not properly compact into thinner grout lines. Non-sanded grout used in lines 1/8" or more will slump, crack, and otherwise not provide proper fill.
- For tile that is easily scratched, such as glass and certain porcelains and ceramics. The sand content in sanded tile grout may damage these surfaces.
Q: What about grout lines that are exactly 1/8"?
A: Your choice, but I recommend using sanded tile grout.
Q: Can I tile a shower floor with sanded tile grout?
A: All other considerations aside--yes.
Q: Will sanded tile grout really scratch tile surfaces during installation?
A: The official response is "yes." In practice, veteran tilers relate that the abrasion from sanded tile grout is likely not enough to scratch tile surfaces. Of course, that is under an expert hand.
Q: Why is unsanded tile grout more expensive than sanded tile grout?
A: At the time of this writing, unsanded tile grout was about 2 1/2 times more expensive than sanded tile grout. This is because sand is cheap and it forms the bulk of sanded tile grout. With non-sanded grouts, more expensive polymers must be added to form the content.
Q: What about for grout lines that are 1/2 or more"?
A: You won't be tiling then. Grout lines rarely exceed a half-inch.