Large-format tile shows every flaw in the floor beneath it. A quarter inch of dip across ten feet disappears under a mosaic and becomes a visible edge under a 24 by 48 slab.
Flatten first
We check floors with a ten-foot straightedge and level them with a self-leveling underlayment before setting. It adds a day to the schedule and removes lippage from the finished floor, which is why leveling is a line item on every tile floor and feature wall we quote.
Full coverage
Big tile gets a large-format mortar, a half-inch notch trowel, and a back-butter on every piece. Hollow corners are how large tile cracks, so we aim for full contact under every edge. The rule holds on walls too, including the large-format panels in a walk-in shower or tub surround.