How do I set out floor tiles so I don't get a sliver at the doorway?

A floor is looked at from the doorway, in raking light, by everyone who walks in. That is the one sightline that matters and it is the one people set out last. Working from the door inwards, and squaring the grid to itself rather than to a wall that is not straight, is what separates a floor that looks laid from one that looks left over.

Safety

What you'll need

• chalk line
• tape measure
• long straight edge
• tile spacers
• enough tiles to dry-lay a full run in both directions
• a builder's square or the 3-4-5 method (optional)

Step by step

1. Check the room for square before anything else.Measure the diagonals. If they differ by more than a few millimetres the room is out of square, and you now know the tile joints cannot be parallel to all four walls — so you choose which walls the taper goes against.
2. Snap two centre lines and prove they are square.Use a 3-4-5 triangle from the intersection: 3 units along one line, 4 along the other, and the diagonal must be exactly 5. A grid squared to itself stays square across the room; a grid squared to a wall drifts.
3. Dry-lay a full run of tiles with spacers in both directions.All the way to the walls. This is the only reliable way to see the real cut widths, and it takes twenty minutes against a floor you cannot change afterwards.
4. Look at what lands in the doorway.A full tile across the threshold looks intentional; a 20mm strip does not, and it is also the piece most likely to crack because it sits over the movement between two floors.
5. Shift the grid to place the cuts where they will not be seen.Under a bath, behind a toilet, under kitchen units and their plinths, along the wall the wardrobes cover. Moving the whole grid half a tile costs nothing at this stage.
6. Check the cut width at both ends of every wall.In an out-of-square room a cut that measures 90mm at one end may measure 45mm at the other. Split the taper between two opposite walls rather than dumping it on one.
7. Mark the perimeter movement gap.The tiling stops a few millimetres short of every wall and every fixed obstacle. That gap is left open and later filled with flexible sealant, hidden by the skirting. Tiling hard into the walls is a common cause of grout cracking round the edges.
8. Mark a movement joint at the threshold.Two rooms are two separately supported floors that move independently. A flexible joint at the doorway rather than continuous grout is what stops a crack forming there.
9. Work outwards from the intersection in quadrants, keeping the lines visible.Lay full tiles across the whole field first, working so you are never kneeling on tiles you have just laid, and finish at the door.
10. Leave the cuts until the field has set, then cut each one individually.Walls are not straight; a cut measured individually fits, a batch of cuts made to one measurement does not.

Tips

• Plan your escape route. Laying yourself into a corner is a genuinely common mistake and there is no graceful recovery.
• In a small bathroom, the visible floor is often only a metre or two: set out for that visible strip, not for the whole room area including under the bath.
• Number the dry-laid tiles with a chinagraph pencil if the tile has a strong pattern or shade variation, then lay them in that order.
• Mix tiles from several boxes as you lay. Shade varies between batches and sometimes within them, and blending is invisible where a block of one shade is not.

Common mistakes

• Squaring the grid to the longest wall — In an older house the longest wall is often the least straight. A grid squared to it drifts progressively across the room, so the joints end up visibly non-parallel to the opposite wall — the fault the eye picks up fastest.
• Tiling tight into the walls with no perimeter gap — The building moves and the floor moves; with nowhere to go, that movement comes out as cracked grout around the edges, hollow tiles at the perimeter, or in the worst case tiles tenting up off the floor.
• Setting out from the middle of the room without checking the doorway — The geometric centre rarely produces a good line at the door. The door is the sightline, so it is the constraint that should be satisfied first and the centre that should be adjusted.

If it doesn't work

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