Ceramic or porcelain
Both are fired clay; the difference is density. Porcelain is pressed harder and fired hotter, absorbs under 0.5% of its weight in water, and is correspondingly tougher and colder to cut. Ceramic is softer, cheaper, easier to cut with a hand cutter and entirely adequate on a wall.
- Ceramic
- Walls, low-traffic floors, anywhere indoors and dry. Cuts easily, chips more easily, costs less.
- Porcelain
- Floors, wet rooms, outdoors, underfloor heating. Needs a diamond blade and more patience; lasts far longer under traffic.
- Full-body porcelain
- Coloured through, so a chip does not show a pale core. Worth it in a commercial or heavily used floor.
- Natural stone
- A different material with different rules: it is porous, needs sealing, and its waste allowance runs higher because the pieces vary.
The ratings on the box
- PEI, wear resistance, I to V
- How well the glazed surface survives foot traffic. PEI I-II are wall or bathroom-floor tiles, III suits ordinary domestic floors, IV covers hallways and kitchens, V is commercial. Buying below the rating you need is how a floor dulls within a year.
- R rating, slip resistance, R9 to R13
- R9 is fine for a dry indoor floor. A bathroom or a kitchen wants R10 or above, an outdoor terrace R11 or more. This one matters more than any aesthetic decision on the page.
- Water absorption
- Under 0.5% is porcelain. Above 3% keeps a tile indoors and away from frost, because absorbed water expands when it freezes and takes the tile with it.
- Rectified
- Edges cut precisely after firing, so the tiles are dimensionally identical and can be laid with a 2 mm joint. Beautiful, and unforgiving: a floor that is out of level shows immediately.
- Calibre and shade
- Printed on every box. Tiles vary slightly between production runs, so mixing batches on one floor produces a visible band. Check these match before the tiler opens the fourth box.
Sizes and what the box tells you
Common European formats are 20 × 20, 30 × 60, 60 × 60 and 120 × 60 cm; American sizes run in inches, where a "12 inch" tile is often 300 mm — which is 11.8 inches, and over ten tiles that is 5 mm of drift.
For an estimate, the tile size is almost a distraction. The figure that matters is the coverage of a box in square metres, printed on the label, because that is the unit the shop sells and the unit you round up to. The tile size only tells you how the cuts will fall.
boxes = ceil(area × (1 + waste) ÷ box coverage)
Large formats need a flatter substrate and a bigger waste allowance, because one bad cut throws away a large piece. Small formats and mosaics waste far less, since the sheet can be cut between tiles.
Buying
- Order the whole job at once, from one batch, and check the batch number on every box at delivery.
- Add 10% for a straight lay, 15-20% for diagonal or herringbone, and more in a room that is out of square.
- Keep at least half a box afterwards. A cracked tile in five years with no replacement means retiling.
- Adhesive and grout are separate purchases sized by area and joint width, and neither is included in a tile count.
- Check the R rating before the colour. It is the one specification that becomes a safety problem rather than an aesthetic one.
PEI and R classifications follow the standards published by tile manufacturers and trade bodies; the exact figures for a product are on its own datasheet. Waste percentages are planning conventions, not standards.