How much tile adhesive per m²?
Adhesive consumption depends mainly on the trowel you use. A larger notch leaves thicker ribs of adhesive, which larger tiles need to achieve full contact and support. As a rule of thumb, the bigger the tile, the bigger the notch — and the more adhesive per square metre.
The calculator picks the notch from the longest edge of your tile:
- Up to 100 mm (mosaic): 4 mm notch, about 1.5 kg/m².
- Up to 300 mm: 6 mm notch, about 2.5 kg/m².
- Up to 450 mm: 8 mm notch, about 3.2 kg/m².
- Up to 600 mm: 10 mm notch, about 4.0 kg/m².
- Over 600 mm: 12 mm notch, about 5.0 kg/m², plus back-buttering at about 1.0 kg/m².
Back-buttering and uneven substrates
Back-buttering means spreading a thin layer of adhesive on the back of each tile as well as on the floor. It is recommended for large-format tiles, natural stone and anywhere the tile must be fully bedded — showers, outdoor areas and heavy-traffic floors. It adds roughly 1 kg/m². On an uneven substrate the adhesive bed has to be thicker in places; the uneven-substrate option adds 15%. If the floor is badly out of level, it is cheaper and better to level it first with screed or self-levelling compound.
The tile adhesive formula
m = A × c × (1 + waste), bags = ⌈ m ÷ bag mass ⌉
A is the floor area in m² and c the consumption in kg/m² from the notch table, plus 1.0 kg/m² for back-buttering and ×1.15 for an uneven substrate. The default adhesive waste is 10%.
Worked example
- Room 4.0 × 3.0 m = 12 m², tiles 600 × 600 mm → 10 mm notch, 4.0 kg/m².
- m = 12 × 4.0 × 1.10 = 52.8 kg → 3 bags of 25 kg.
- With 600 × 1200 mm tiles: 12 mm notch and back-buttering, 5.0 + 1.0 = 6.0 kg/m² → 12 × 6.0 × 1.10 = 79.2 kg → 4 bags.
Cement-based adhesive on anhydrite screed
Anhydrite (calcium sulphate) screeds react with cement-based adhesives: the gypsum and cement form ettringite at the interface, which can cause tiles to debond. If you choose anhydrite screed in the full calculator and a cement-based adhesive, a primer before tiling is added automatically to separate the two. Alternatively, use an adhesive approved for calcium sulphate substrates.
Mixing and open time
Mix only as much as you can use within the adhesive’s pot life, typically two to four hours, and spread only as much as you can tile within its open time, often 20–30 minutes. Comb the adhesive in straight lines in one direction and press each tile in across the ribs. Lift a tile occasionally to check the coverage on the back.
Frequently asked questions
How many m² does a 25 kg bag of tile adhesive cover?
About 10 m² with a 6 mm notch, 6–7 m² with a 10 mm notch and 4–5 m² with a 12 mm notch and back-buttering.
Which trowel notch should I use?
Follow the table above as a starting point and the adhesive manufacturer’s guidance. Check coverage by lifting a freshly laid tile: the back should be at least 80% covered on floors, fully covered in wet areas.
Can I use cement-based adhesive on anhydrite screed?
Only with the right primer between them, or use an adhesive approved for calcium sulphate screeds. The calculator adds the primer automatically when it detects this combination.
Do I need flexible adhesive?
Use a flexible (S1) adhesive on underfloor heating, timber bases and for large-format porcelain. The quantity per m² is the same.