I have seen a bathtub made completely of tile. How does the tile hold water? I know that tile alone will hold water but grout won’t. I really want to make a tile bathtub, but can you please advise me how to make a tile bathtub waterproof?
You are correct that the bathtub tile grout will not hold water. In this case, the tub is not waterproof, but the material beneath the tile tub is. When learning how to build a tile bathtub, you will first have to construct the tub, then line it with a water proof material like fiberglass, then adhere the tile to the bathtub.
This is basically what is done when constructing a tile show pan for a shower stall. Building a tile bathtub is not a simple do-it-yourself project, so if you really want a fancy tub, you might be better off just buying one!