What size trowel for tile?

Trowel size chart

From Custom Building Products’ notch series guide and trowel catalog. A notch is given as width × depth × the space between notches. Its premium trowel brochure groups the same three square notches as up to 8 in, 8 to 16 in and over 16 in. Custom says to always follow the mortar maker’s notch recommendation, and the TCNA notes it is printed on the bag.

By tile

• Mosaic sheets (small tiles on a sheet): each tile is well under 8 in, so the chart’s notches for tile 8 in or smaller apply, such as the 1/4 × 1/4 in square notch in thin-set. On a shower floor, aim for the wet-area coverage below.
• Subway tile, 3 × 6 in: a wall tile of 6 in or less, so a 3/16 × 5/32 in V notch with adhesive, or a 1/4 × 1/4 in square notch with thin-set.
• 12 × 12 in floor tile: in the 8 to 16 in group, a 1/4 × 3/8 in square notch. Custom also lists a 1/4 × 1/2 in U notch for tile 12 in or larger.
• 12 × 24 in tile, floor or wall: its long side is 24 in, past the 15 to 16 in mark, so a 1/2 × 1/2 in square notch. Custom’s mortar sheet warns that larger tiles may need a larger notch and back-troweling, a thin coat of mortar on the back of the tile, to reach full coverage.
• Large format and plank tile (24 × 24, 24 × 48, 8 × 48 in): a 1/2 in square notch, or the 3/4 × 9/16 × 3/8 in U notch with a medium-bed or large-format tile mortar.

Two tiles of the same size can still need different notches: Custom notes that tiles with a deep pattern on the back, and natural stone that isn’t gauged to an even thickness, may need a larger notch.

Coverage: the test that matters

The notch is a starting point. What counts is how much of each tile’s back ends up bedded in mortar. Custom’s VersaBond data sheet requires at least 80% coverage in dry areas and 95% in wet areas and outdoors, with every edge of the tile supported. Schluter calls notched trowels “metering devices” and says to never assume a notch size guarantees coverage: check it now and then during the job.

• Test it. Custom recommends testing to confirm the coverage: set a tile, lift it back up and look at its back for bare spots where the ridges didn’t collapse.
• Flatten the ridges. The Tile Council of North America says tiles 10 × 10 in and larger need to be slid or rotated into the mortar, or they leave voids that can make them break or come loose.
• Don’t level with mortar. Thin-set is meant to be thin: about 3/16 in under the tile, which is what a 3/8 in notch leaves once the tile is pressed in, by the TCNA. The tile follows the floor or wall beneath it. Custom gives 3/32 to 1/4 in after the tile is set, for mortars without an ANSI “H” rating.

How much thinset each notch uses

Coverage for Custom’s VersaBond, a 50 lb bag, from its product page; bags round up at the low end of each range. Back-troweling uses more.

The bigger the notch, the more mortar: a bag spread with a 1/2 in notch covers about half the floor it would with a 1/4 in one. Floor areas of common bathrooms are in standard bathroom size. Our tile calculator works out the boxes of tile for your room, the bags of thinset for each of these notches and the grout.

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