There's no single right trowel — the notch size depends on the tile. As a starting point: roughly 6–8mm for standard wall tiles, 8–10mm for floor tiles, and 10–12mm or bigger for large format. But the number is only a guide. What actually matters is the adhesive coverage on the back of the tile, and the way you check that is to lift one and look. Here's how to pick the notch and get it right.
Key Takeaways
- Wall tiles: typically a 6–8mm notch (smaller for mosaics, ~4–6mm).
- Floor tiles: typically 8–10mm — bigger, heavier tiles need more adhesive.
- Large format: 10–12mm or more, plus back-buttering.
- The number is a guide. Coverage on the back of the tile is what counts.
- Lift a tile early to check coverage, and go up a notch if it's thin.
What the notch actually does
The notched edge of a tiling trowel combs the adhesive into even ridges. When you press the tile in, those ridges collapse and spread to form the bed the tile sits on. The size of the notch sets how much adhesive ends up under the tile:
- Too small → not enough adhesive, the tile doesn't get full contact, and it can sound hollow or work loose.
- Too big → too much adhesive, it squeezes up through the joints and you waste material.
Match the notch to the tile and you get a solid, flat, well-bonded tile. That's the whole job of choosing a trowel.
Typical trowel sizes by tile
Treat these as sensible starting points, not gospel — manufacturers' guidance varies, and coverage is the real test.
| Tile | Typical notch size | |---|---| | Mosaics / very small tiles | 4–6mm | | Standard wall tiles | 6–8mm | | Standard floor tiles | 8–10mm | | Large format (600mm+) | 10–12mm or larger, plus back-buttering |
The pattern is simple: bigger, heavier tiles need a bigger notch and a thicker adhesive bed. A small wall tile floats on very little; a 600×1200mm porcelain slab needs a proper bed under every part of it.
Why coverage beats the number
Here's the bit most guides skip: the notch size is a means to an end, and the end is coverage.
Lift a freshly laid tile early in the job and look at the back. You want adhesive transferred across almost the whole back of the tile — a solid bed, not a few stripes with bare gaps between them. If the coverage looks thin or patchy:
- Go up a notch size, or
- Back-butter the tile (more on that below), or
- Check your adhesive consistency — too dry and it won't transfer.
In wet areas and on floors you want coverage as close to full as you can get — gaps under a floor tile are weak points that crack, and gaps behind a shower tile are voids that hold water.
Back-buttering: the large-format must-do
For big tiles, the trowel alone often won't give you full coverage, so you back-butter: spread a thin, even layer of adhesive onto the back of the tile as well as combing it onto the floor or wall. The two beds meet and fill the gaps the ridges leave.
It's standard practice for large-format and heavy tiles, and it's covered as part of the method in the large format tile installation guide. Skip it on a big tile and you'll get hollow spots and lippage.
Match the adhesive to the job too
The trowel is half the story — the adhesive matters as much. Wall tiles, floors, wet areas, and heavy porcelain all want different adhesive, and the right one combs and holds far better. The tile adhesive buying guide covers which class goes where, and the notch sizing pairs straight with it.
The short version
Start with 6–8mm for walls, 8–10mm for floors, 10–12mm-plus for large format — then lift a tile, check the coverage, and adjust. Get a solid bed under every tile and they'll still be there in twenty years. That's all the notch is really for.
Related guides
- Tile adhesive buying guide — the adhesive that pairs with the notch
- How to tile a wall — trowel work in context
- Large format tile installation — back-buttering and big-tile beds
- The complete UK tiling tool kit — trowels and the rest of the kit