Large-format tile
Also called: LFT, large format porcelain, 24x48 tile, oversized tile, porcelain slab, gauged porcelain panel, big tile
Tile with any side 15 inches or longer — 12 × 24, 24 × 24, 24 × 48 and up to 5 × 10 foot porcelain panels. Fewer grout lines, but the rules tighten: a floor flat to 1/8 inch in 10 feet, heavy-tile mortar, back-buttering, a leveling system, a 33% offset, and two people for the big ones.
The industry definition is any tile with a side of 15 inches or more, which makes the 12 × 24 that’s now the default floor tile technically large-format — and explains why so many first-time tile floors go wrong. The bigger the tile, the more its own bow and the floor’s unevenness show at the joints, the harder it is to get mortar under the whole back, and the heavier it is to place and slide into position. A 24 × 48 porcelain weighs about 40 pounds; a 5 × 10 foot panel needs frames, suction cups and a crew.
What changes, in order. Flatness: the substrate has to be within 1/8 inch in 10 feet and 1/16 in 2 feet, tighter than the 1/4 in 10 allowed under small tile, which usually means self-leveling underlayment on any floor that isn’t new. Mortar: large-and-heavy-tile (LHT, formerly “medium bed”) mortar that won’t slump under the weight, combed with a 1/2-inch notch, and the tile back-buttered, for 80% coverage on a dry floor and 95% in a wet area or on any tile over 15 inches. Layout: a 33% offset instead of 50%, because a bowed tile’s high center next to a neighbor’s low end is unavoidable lippage at half offset. Leveling clips on every joint. Cutting on a saw that can take the length, or a rail cutter for panels. And two people for anything over 24 × 24.
The reward is a floor with a third of the grout lines and the look of stone or a slab. The cost is that it’s a setter’s job, or a very experienced homeowner’s — the cost page puts the 24 × 48 tier on the hire side, and the DIY guide stops at 12 × 24 with a leveling system.