Notched trowel
A notched trowel lays tile adhesive in controlled-depth ridges. Notch size (6, 10, 12 mm) chosen for tile size. Wrong notch causes low coverage and hollow tiles.
Ask Chalkline about this →A notched trowel is the specialist tile trowel with rectangular, U-shaped, or V-shaped notches cut into one or two edges of the steel blade. The notches lay the tile adhesive (thin-bed cementitious or mastic) in ridges of controlled height, which then compress under the tile to deliver a target coverage thickness. Without the notches, an adhesive bed is uneven; with them, the bed is predictable and full.
Notch profiles:
- Square notch: rectangular cut, used for floor tiles and large-format wall tiles. The most common profile in Australia.
- U-notch: rounded-bottom cut, used for some adhesive types and large-format thin tiles where flow under compression is needed.
- V-notch: triangular cut, used for small wall tiles, glass tiles, and mosaics. Lays thinner ridges.
The handle is wood, plastic, or rubber-coated; the blade is steel, typically 200 to 300 mm long.
Notch size selection under AS 3958.1:
| Notch size | Tile size | Typical use |
|---|---|---|
| 4 mm V | Mosaics, glass tile up to 100 × 100 mm | Decorative inserts, glass-tile feature walls |
| 6 mm square | Wall tile up to 300 × 300 mm | Standard bathroom wall tiles |
| 8 mm square | Wall tile up to 400 × 400 mm; small floor tile | Medium wall tile |
| 10 mm square | Floor tile 300 × 600 to 600 × 600 mm | Volume residential floor tile |
| 12 mm square | Floor tile 600 × 1200 mm and larger | Large-format porcelain |
| 15 mm + back-butter | Large-format > 1200 mm; natural stone | Specialised work, often combined with mortar bed |
Bigger notches lay more adhesive at higher ridge height. Wrong-direction notches (notch perpendicular to the tile’s long axis instead of parallel) leave air gaps that cannot collapse. Always lay ridges in the same direction; perpendicular cross-hatching is a defect.
Full coverage rule. AS 3958.1 requires:
- Wall tiles: minimum 65% coverage of the tile back by adhesive.
- Floor tiles: minimum 85% coverage, especially on tiles ≥300 mm.
- External and wet area tiles: minimum 90 to 95% coverage.
Achieving these coverages on large-format tile requires back-buttering in addition to the notched-trowel bed. The combination is what AS 3958 expects on any tile larger than 300 × 300 mm.
Common defects from wrong trowel use:
- Hollow tiles: notch too small for the tile size. Tap-test shows hollow corners; tile cracks on later impact.
- Insufficient adhesive: notch too small or trowel held at too shallow an angle. Hollow tiles also.
- Slumped ridges: notch was right but adhesive over-mixed (too wet); ridges collapse before tile is laid.
- Voids at perimeter: notch ridges run parallel to a wall and the tile bottoms out on a thinner spot.
For builders.
- Confirm the tiler is using the right notch size for the spec’d tile. Check the trowel; ask if back-butter is being done on tiles over 300 mm.
- Tap-test before grout. Hollow tiles can be removed and re-bedded before grout; after grout the cost is multiples.
- Order more adhesive than the basic coverage calc suggests. Back-buttering plus full-bed notching uses 25 to 40% more adhesive than the bag-cover estimate.
Also known as: tile trowel, notch trowel, adhesive trowel.
Category: Practical / tiling / tools.
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Last updated: 2026-05-14. Verified: 2026-05-14.