Guide · 6 min read
Large-format tile: what to know before you buy it
By Josh, owner & lead installer at Blue Diamond Tile & Stone · Published
Short answer
Large-format tile — any tile with a side over 15 inches — needs a floor flat to 1/8 inch in 10 feet, a large-and-heavy-tile mortar with the tile back-buttered, a maximum one-third offset on rectangular tile, and leveling clips. Without those, you get lippage: edges that catch your foot and shadows that show every seam.
What counts as large-format tile?
The industry standard draws the line at 15 inches: any tile with at least one side longer than that is large-format and falls under stricter installation requirements. That includes 12×24 planks, 24×24 squares, 24×48 slabs and the 48×48 and larger formats, up to gauged porcelain panels that cover a whole shower wall in one piece.
How flat does the floor need to be?
Flat to 1/8 inch in 10 feet and 1/16 inch in 2 feet. For small tile the tolerance is twice that. The reason: a long tile bridges low spots and rocks on high spots instead of following them, and every irregularity shows up as lippage between neighboring tiles. Concrete slabs in the valley are rarely that flat as poured, so grinding high spots and self-leveling low ones is part of nearly every large-format floor — and it's the part of the estimate people don't expect.
What is lippage and why does the offset matter?
Lippage is the height difference between the edges of two adjacent tiles. Some is unavoidable; too much catches feet and looks like a mistake in raking light. Large porcelain tiles have a slight bow from the kiln — the center is a hair higher than the ends. In a 50 percent brick pattern the high center of one tile lands next to the low end of the next, and no leveling system can flatten that. The rule is an offset of no more than a third on rectangular tile over 15 inches.
What does a proper large-format installation include?
The things a good installer does that a fast one skips:
- A straightedge survey of the floor before quoting, with flattening priced separately
- A large-and-heavy-tile mortar (ANSI A118.15) with the correct trowel and the tile back-buttered
- Mortar coverage checked by pulling a tile — at least 80 percent indoors, 95 percent in wet areas and outdoors
- A layout planned for a one-third maximum offset and balanced cuts at the walls
- Leveling clips or wedges on every tile until the mortar sets
- Movement joints where the room's length or the slab's control joints call for them
Why does large-format tile cost more to install?
The prep. Flattening a slab is slow, dusty work that doesn't show in the finished floor but decides whether it's flat. The tile is heavier and takes two sets of hands; cuts are made on a bigger saw and wasted cuts cost more; leveling systems are consumable. Expect installation to be a bigger share of the total than it would be with 12×12 tile, and be suspicious of a quote that doesn't mention flatness at all.
Fair questions
FAQCan large-format tile go over an existing tile floor?
Only if the existing floor is sound and already flat to 1/8 inch in 10 feet, which old floors rarely are. In most valley homes the old tile comes up and the slab is flattened — more work and a far better floor.
Why do my new large tiles have uneven edges?
Lippage: the floor wasn't flat enough, the offset was 50 percent on bowed tile, or no leveling system was used. Isolated high edges can sometimes be ground; widespread lippage means resetting tiles over a flattened slab.
What offset should 24×48 tile be laid at?
No more than a third — about 16 inches on a 48-inch tile. A half offset lines up the high centers with the low ends and guarantees lippage on any tile with a bow.