Do Large Tiles Sound Hollow More Often Than Small Ones?

Yes. Large-format tile — defined by ANSI A137.1 as any tile with at least one edge measuring 15 in or longer — reports hollow spots more often than smaller tile, and the reason is arithmetic, not bad luck. ANSI A108.5 sets a minimum mortar coverage of 80% for interior dry floors and 95% for wet or exterior installations, the same rule for every tile size. A small tile only has to stay flat across a short run of ridge-and-furrow trowel pattern to hit that percentage; a large tile has to stay flat across a much bigger area, so any dip in the slab shows up as an uncollapsed ridge and a void underneath instead of getting averaged out over many small tiles and grout joints.

Substrate flatness tolerance tightens for the same reason. ANSI A108.02 allows 0.25 in (1/4 in) per 10 ft of deviation for standard-size tile, but drops that to 0.125 in (1/8 in) per 10 ft for large-format tile, plus a local check of 0.0625 in (1/16 in) per 24 in. A floor that would pass the standard-size check can still fail that tighter local check once large-format tile goes down, and the failure shows up later as a hollow ring when someone taps the surface rather than as a visible crack.

The table below lines up the two rule sets side by side. The coverage percentage doesn't change with tile size — it's still 80% dry, 95% wet — but the flatness tolerance, trowel size, and back-buttering requirement all get stricter once an edge crosses 15 in.

TCNA Handbook installation methods call for back-buttering — troweling a skim coat of mortar onto the back of the tile in addition to the substrate — on any tile with an edge longer than 12 in, because a single-sided trowel pass can't reliably fill the gap where the floor dips even slightly under a large tile. A 0.5 in by 0.5 in square-notch trowel is the size most manufacturers specify for large-format floor tile, larger than the notch used on smaller tile, because bigger ridges hold more mortar and collapse more evenly under a heavier, larger piece.

Skip the tighter flatness check or the back-buttering step and the void doesn't stay quiet. Foot traffic flexes the tile over the hollow spot, and because a large tile spans a longer unsupported distance than a small one, the flex concentrates stress at the edges instead of spreading across many grout joints the way it would on a small-format floor. That's the mechanical reason large-tile lippage and cracking show up disproportionately at the perimeter of a hollow area rather than as a small chip in the middle — the tile lippage guide walks through how that stress pattern develops over time.

In wet areas the stakes go beyond sound. The 95% coverage requirement exists because a wet-area floor without near-total mortar contact lets water track under the tile through the grout joints and sit in the voids, which is how mold and substrate rot start under an otherwise intact-looking shower or entry floor. A hollow tap in a kitchen is usually a cosmetic risk; the same tap on a curbless shower pan is a moisture-management problem, and the hollow-sounding floor tile guide covers how to tell which one you're dealing with.

Substrate matters as much as tile size. A plywood subfloor moves more than a slab and is harder to flatten to the 0.125 in per 10 ft tolerance without a self-leveling underlayment pass, so large tile over plywood needs more prep than the same tile over a properly cured slab; the plywood subfloor prep guide covers the leveling and membrane steps that close that gap.

Installer technique closes most of the rest of it. Full back-buttering, working the trowel in one direction, and pulling a test tile after the first placement to check the mortar pattern all catch a void before it gets grouted over. If you're sizing a large-format floor before you buy, run the layout through the floor tile calculator to see how many full tiles versus cuts you'll get, and check joint width on the tile spacing calculator — a slightly wider joint on large tile gives a little more room to true up an uneven substrate without forcing lippage at the edges.