Buying tile exactly to the size of the bathroom is risky: there are always cuts at corners, door junctions and pieces that break when handled. The question isn't just "how many m² is the wall", but how much margin to add for the format and which adhesive suits each material.
The cutting margin depends on the format and the material
The general rule is 10% waste over the measured area, but it varies by tile:
- Glazed wall tile, porcelain stoneware, small-format tile or encaustic tile: +10%.
- Mosaic or small-tile mesh sheets: +12%, because being mounted on meshes of small pieces there are more adjustments at the edges.
Example: to tile 8 m² of wall with 20×20 cm tile: 8 × 1.10 = 8.8 m² to buy. This is the same calculation the PresupuestoYa calculator applies automatically for the Tiler trade.
The format determines more than it seems
- Small formats (10×10 to 20×20 cm) hide an uneven substrate better.
- From 30×60 cm, any irregularity in the wall shows up far more and it's wise to regularise before tiling — don't try to compensate for an out-of-level wall just with a thicker layer of adhesive, because a layer that is too thick may not cure properly and lose grip.
- From 45×45 cm it is advisable to use a levelling system to avoid steps between neighbouring pieces (lippage), especially under raking light.
Which adhesive suits each material
Not all tile is laid with the same tile cement, and choosing the wrong one compromises grip in the medium term:
| Adhesive | Consumption | When to use it |
|---|---|---|
| Tile cement C1 (standard) | 4.5 kg/m² | Standard tile on traditional masonry, firm substrate |
| Flexible adhesive C2 | 6 kg/m² | Porcelain, large pieces, or a deformable substrate (plasterboard, underfloor heating) |
| Adhesive for natural stone | 5 kg/m² | Marble, travertine and porous stones — avoids stains from salt migration |
| Epoxy adhesive | ~4 kg/m² | Permanent immersion (swimming pools), sets fast and doesn't allow adjustment |
In practice, C2 is mandatory for porcelain or large format: C1 doesn't offer enough adhesion or flexibility for those pieces.
Complete worked example
To tile an 8 m² bathroom with 60×60 cm porcelain stoneware (C2 adhesive):
- Tile: 8 m² × 1.10 = 8.8 m² to buy
- Adhesive: 8 m² × 6 kg/m² = 48 kg → 2 bags of 25 kg
Frequently asked questions
Why does mosaic take more margin than normal tile? Because it's mounted on a mesh of small pieces and generates more adjustments and offcuts at the edges: 12% against the standard 10%.
Can I use C1 tile cement for large-format porcelain? It isn't recommended: low-absorption, large-format porcelain needs a C2 adhesive, with more adhesion and flexibility.
Is primer needed before tiling? Yes, if the substrate is low-absorbency or dusty (old paint, very smooth concrete), or if you will tile directly over a well-bonded old tile without breaking it out.
Conclusion
Calculating the cutting margin by format and getting the right adhesive avoids two costly problems: running out of tiles from the same batch halfway through the bathroom, or tiling that comes off over time through using insufficient tile cement. Automating it gives a tight and technically correct materials quote.
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