Common Mistakes When Tiling a Floor (Waste, Boxes, Grout)
A tile that runs out in the last row is a real problem, because tiles from a new lot may not match. A 12 × 10 ft floor tiled with 12 in tiles takes 130 tiles (13 boxes of 10) including 10% extra. The tile calculator works out yours. Here is what goes wrong.
Part of the project planner: Planning new floors and tile.
Mistake 1: not enough waste
Cuts at the edges, breakage and mistakes all use tiles. For the example floor:
| Extra allowed | Tiles | Boxes of 10 |
|---|---|---|
| 5% | 124 | 13 |
| 10% | 130 | 13 |
| 15% | 136 | 14 |
| 20% | 142 | 15 |
A diagonal layout, or a floor with many corners, wants the higher figure.
Mistake 2: rounding the boxes down
Tile is sold by the box, and the last box is nearly always part used. Always round up to whole boxes, and keep a spare box or two in the garage for repairs. Tiles for the same floor in different sizes:
| Tile size | Tiles | Boxes of 10 |
|---|---|---|
| 4 × 4 in | 1118 | 112 |
| 6 × 6 in | 507 | 51 |
| 12 × 12 in | 130 | 13 |
| 12 × 24 in | 65 | 7 |
| 24 × 24 in | 33 | 4 |
Mistake 3: ignoring the grout joint
Joint width changes both the tile count and the grout. For 6 × 6 in tiles on the same floor:
| Joint | Tiles | Grout |
|---|---|---|
| 0.0625 in | 518 | 9.4 lb |
| 0.125 in | 507 | 18.8 lb |
| 0.1875 in | 497 | 28.1 lb |
| 0.25 in | 487 | 37.5 lb |
Check the joint width the tile maker recommends, since some rectified tiles are set with a very narrow joint.
Mistake 4: a poor start line and an uneven floor
Do not start against a wall, because walls are rarely straight. Snap a center line, dry lay a row each way and adjust so that you do not end with a thin sliver of tile at one edge. Flatten bumps and fill dips first: a floor that is out of flat makes lippage between tiles whatever the skill of the tiler.
Mistake 5: wrong thinset, trowel or timing
- Use the trowel notch the tile size needs: larger tiles need a deeper notch for full contact.
- Press each tile in and lift one now and then to check that the back is covered.
- Do not mix more thinset than you can use before it skins over.
- Let the thinset cure before grouting, and wipe the grout haze off before it hardens.
For thinset, grout, backer board and tools in one list, use the tile project materials calculator. Estimates only: check coverage with the products you buy.
Frequently asked questions
How much extra tile should I buy?
About 10% for a plain straight layout, and 15% or more for diagonal patterns, small rooms with many cuts or large tiles. For 120 sq ft of 12 in tile: 130 tiles at 10%, 136 at 15%.
Why buy all the tile at once?
Tiles from different lots can differ in shade and size, so buying it all together, with the spares, avoids a mismatch if you need more later.
Does the grout joint change how many tiles I need?
A little: wider joints take up more of the floor, so you need fewer tiles but more grout.
How do I know how much thinset to buy?
It depends on the trowel notch and the tile size. For the example floor the calculator gives 2 bags, but check the coverage on the bag.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.