Without some degree of surface preparation, it’s highly unlikely that a concrete slab or wood-framed subfloor will be flat enough to meet the requirements for large-format tile. A quick check with a straightedge often shows that a small area or perhaps the entire surface dips and undulates outside of industry standards.
Before installing your beautiful new flooring, the most important step is to consider how much moisture is in your concrete slab. This measurement is referred to as the moisture vapor emission rate (MVER).