Common Mistakes When Tiling a Floor or Wall (UK): Waste, Grout
A tile that runs out in the last row is a bad day, and a new batch may not match. A 3 × 2.5 m floor with 300 mm tiles and 3 mm joints takes 90 tiles with 10% extra, which is 9 boxes, with 37 kg of adhesive and 2.9 kg of grout. The tile calculator sizes your job.
Mistake 1: not enough waste
Cuts, breakage and awkward corners all use tiles:
| Extra | Tiles | Boxes of 1 m² |
|---|---|---|
| 5% | 86 | 8 |
| 10% | 90 | 9 |
| 15% | 94 | 9 |
| 20% | 99 | 9 |
Mistake 2: forgetting that tile size changes the count
For the same floor:
| Tile size | Tiles |
|---|---|
| 100 × 100 mm | 778 |
| 150 × 150 mm | 353 |
| 300 × 300 mm | 90 |
| 300 × 600 mm | 46 |
| 600 × 600 mm | 23 |
Mistake 3: the wrong grout joint
Joint width changes the tile count and the grout. Use the width the tile maker advises:
| Joint | Tiles | Grout |
|---|---|---|
| 2 mm | 91 | 1.9 kg |
| 3 mm | 90 | 2.9 kg |
| 5 mm | 89 | 4.8 kg |
| 10 mm | 86 | 9.6 kg |
Mistake 4: the wrong trowel
A notch that is too small leaves air under the tile. Adhesive for the example floor:
| Trowel notch | Adhesive | Bags |
|---|---|---|
| 3 mm | 24.8 kg | 2 |
| 4.5 mm | 37.1 kg | 2 |
| 6 mm | 49.5 kg | 3 |
Mistake 5: an uneven base and a poor start line
- Level and prime the floor first: a screed or levelling compound fixes dips, and the screed calculator sizes it.
- Find the centre of the room, and dry lay a row each way to avoid thin slivers at the edges.
- Press each tile in, lift one now and then to check coverage, and wipe off adhesive and grout haze quickly.
For adhesive, grout and tools on one list use the tiling materials calculator. Estimates only: check coverage on the pack.
Frequently asked questions
How many tiles do I need for a 3 × 2.5 m room?
With 300 × 300 mm tiles, 3 mm joints and 10% extra, 90 tiles, which is 9 boxes of 1 m².
How much extra should I order?
Ten percent for plain layouts, and 15 percent or more for diagonals, small rooms, large tiles or a lot of cuts: 94 tiles at 15%.
Does the trowel size matter?
Yes: larger tiles need a bigger notch for full contact, and the adhesive quantity changes. See the table.
Do I need to prime the surface?
Often, especially on absorbent or very smooth surfaces. Follow the adhesive maker instructions.
More guides
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.