The right trowel size is the one that gets full mortar coverage under your tile. For most jobs, start with the notch in the chart below, set a tile, then pull it up and check the back. The chart gets you close. The pull test tells you if you're right.
Coverage matters because the industry standard (ANSI A108.5) calls for at least 80% mortar contact in dry interior areas and 95% in showers, wet areas and exteriors. Voids under tile lead to cracked tile, hollow spots and lippage. Most failed tile jobs trace back to the wrong notch or poor troweling, not bad tile.
Trowel notch size chart
Use these as starting points. Tile flatness, substrate flatness and mortar type all change what you need.
| Tile size | Starting notch | Back-butter? | Trowels we stock |
|---|---|---|---|
| Mosaics, 2" and smaller | 3/16" V-notch | No | Marshalltown V-notched margin trowel |
| Up to 8" (4x4, 6x6, 3x12 subway) | 1/4" x 1/4" square notch | No | HUDS NotchTile Copper 1/4", Marshalltown QLT |
| 8" to 12" | 1/4" x 3/8" square notch | Optional | Marshalltown Durasoft notched trowels |
| 12" to 16" (12x12, 13x13, 16x16) | 3/8" x 3/8" square or slant notch | Recommended | HUDS NotchTile Graphite 3/8", Raimondi 3/8" slanted notch |
| Large format, any side 15" or longer (12x24, 24x24, 24x48) | 1/2" x 1/2" square, slant or U-notch | Yes, every tile | HUDS NotchTile Gold 1/2", Rubi YW large format trowel |
| Wood-look plank (6x36, 8x48) | 1/2" square or slant notch | Yes, every tile | Marshalltown 16" LayFlat |
| Over Schluter Kerdi or Ditra | The notch the membrane maker specifies | Per spec | Schluter Kerdi square notched trowels |
For tile with any edge 15" or longer, use a mortar rated for large and heavy tile (LHT). Standard thinset can slump under the weight before it cures.
How to tell if your notch is right: the pull test
- Comb mortar in straight, parallel lines. Never swirl it. Swirls trap air that can't escape.
- Set the tile and slide it about 1/4" across the ridges, then back. This collapses the ridges.
- Pull the tile up right away and look at the back.
- Full contact with only thin stripes of bare tile means you're good. Bare corners, edges or a striped pattern mean you need a bigger notch, a back-butter coat, or both.
Check the first few tiles, then every so often as the job goes on. Mortar stiffens in the bucket, and coverage drops with it.
Five things that change your trowel size
- Tile warpage. Large porcelain is rarely perfectly flat. Cupped or crowned tile needs a deeper notch to fill the gap.
- Substrate flatness. Large format tile needs a flat floor, typically within 1/8" in 10 feet. A bigger notch is not a fix for an out-of-flat floor. Level it first.
- Textured backs. Deep lugs or ribs on the tile back need more mortar. Back-butter to fill them.
- Mortar type. Medium bed and LHT mortars hold a taller ridge. Thin, wet mortar slumps and needs a larger notch.
- Trowel wear. Steel notches wear down on rough substrates. A 1/2" notch can drop to 3/8" after a few big jobs. Replace worn trowels or swap blades on a switchable set like the BIHUI 9-piece switchable notched trowel set.
The real installer debate: square notch vs. slant notch
Ask ten setters and you will hear both sides.
The square notch camp says it is predictable. Every ridge is the same height, so you know how much mortar is going down and you can check it by eye. It is what most manufacturer charts are written around.
The slant and euro notch camp says angled ridges collapse with less effort and leave fewer voids, especially on large format and plank. Many pros running 24x48 or longer swear they get better coverage with less back-buttering. Trowels like the Raimondi slanted notch and Primo Tools euro style are built for this.
Where it lands: both work when coverage is right. Pick the one you can comb consistently, then prove it with the pull test. On big tile, many setters run a slant notch on the floor and still back-butter. Coverage is the goal, not the notch shape.
Common mistakes
- Using one trowel for everything. A 1/4" notch under 24x24 tile almost always fails coverage.
- Spreading too much mortar at once. If it skins over before the tile goes down, it will not bond. Spread only what you can set in 10 to 15 minutes.
- Skipping the back-butter on large tile. Thin-coat the back with the flat side of the trowel before setting.
- Troweling at a low angle. Hold the trowel at about 45 to 60 degrees so the notches reach full depth.
Frequently asked questions
What size trowel for 12x24 tile? Start with a 1/2" x 1/2" square or slant notch, use LHT mortar, and back-butter every tile.
What size trowel for subway tile on a wall? A 1/4" x 1/4" square notch works for most 3x6 and 3x12 subway tile. Use a 3/16" V-notch for thin glass or small mosaics.
What size trowel for 24x24 tile? A 1/2" x 1/2" notch with back-buttering is the usual start. Check coverage early; warped tile may need a 3/4" U-notch.
Can I use a bigger notch to be safe? Too much mortar causes its own problems: squeeze-out in joints, lippage and slow cure. Use the smallest notch that passes the pull test.
Shop our full line of notched trowels from Marshalltown, Rubi, Raimondi, HUDS, BIHUI and QEP, plus large format tile tools for leveling, lifting and cutting big tile. Pro pricing, fast shipping, and real people on the phone who know tile.