What purpose does it serve? Is it safe to assume the tile will settle half of the trowel thickness? For example, if using a 1/4 inch trowel, will the tile settle 1/8 inch when set in place? Thanks for any help/advice!
Guitar is mostly right. You need the correct size trowel to spread it uniformly to set the tile in place so the thin set will both bond the tile to your substrate and provide the correct coverage to support the tile . Different trowels for different applications. You don t rely on the tile settling into place you have to set it, slightly press it and use a slight twisting motion to get the coverage you need to conform to specs in the ATC tile hand book, Any questions you can e mail me through my avatar and check my qualifications there. GL
Thinset cements the tile to the subfloor. The settling depends on the tile, and whether or not you press it down.
The trowel is used to spread the thinset, and even it out to a uniform thickness.