Get the tile ratio right before anything else

Herringbone only works with a true 2:1 rectangle. A 600 x 300mm porcelain tile, a 300 x 150mm wall tile, a 200 x 100mm brick-shaped tile — all of these will interlock neatly because the long edge is exactly twice the short edge. What they say on the box is a nominal size, though, and tiles can vary by a millimetre or so between batches. On a small splashback that hardly matters. Across a hallway floor, a tiny variation compounds with every course until the pattern has visibly drifted and your joints are opening and closing like an accordion.

Before you commit, take four or five tiles from the boxes you intend to use and measure them properly with a steel rule or digital calliper. Check the length, the width and the squareness of the corners. If one tile is 598mm and another is 602mm, put them back and choose something else, or accept that you will be fighting the pattern all day. It also pays to buy all the tiles in one go, from the same batch, with a few spare for cuts and breakages.

Find the centre and fix a datum you can trust

Setting out is the whole job. Everything after that is just trowel work.

Start by finding the centre of the room in both directions, but don't be a slave to it — the main sight line matters more. In a hallway, that usually means looking in from the front door. In a bathroom, it's the view from the doorway across to the far wall. Mark the room's centre point, then snap a chalk line along your chosen sight line. Check it's genuinely central to the space people will see, not just mathematically exact.

Next, establish a true 90° from that line. The oldest trick still works: measure 3 units along one line, 4 along the other, and adjust until the diagonal between them is 5. Use metres rather than centimetres for better accuracy on a large floor, or a big folding square if the room is small.

• Snap your primary datum line along the main sight line.
• Create a second line at exactly 90° to it, crossing at the centre point.
• For a classic diagonal herringbone, mark lines at 45° to the datum by stepping equal distances either side of the centre and joining the marks.
• Pencil the pattern lines onto the substrate as well as chalking them, so you can re-establish them after a break or once the adhesive starts going off.

Dry lay the first courses and watch for drift

Never start sticking tiles straight from the box. Dry lay at least six to ten tiles along your datum, following the herringbone sequence exactly. Two tiles form a square of the long edge; that square is the module the whole floor repeats from, and it will tell you very quickly whether the pattern wants to behave.

Look for three things. First, are the joints consistent? Second, does the pattern stay parallel to your marked line as it steps away from the centre? Third, when you place a long spirit level or straight edge across the dry-laid tiles, does everything sit flat and true, or are you seeing gaps that suggest out-of-square tiles?

If the pattern wanders, stop. Almost always it's the tile ratio, not your technique. Sorting it now costs you nothing. Sorting it after twenty square metres are fixed means lifting tiles and starting again.

Plan your cuts before you commit

Once the dry lay looks right, walk the perimeter and work out what your edge cuts will be. In herringbone you will always get angled cuts at the walls, and they look best when they are reasonably generous — aim for at least a third of a tile, and avoid slivers wherever you can.

Check the walls for square. Very few British rooms are, especially in older houses. If one wall runs out by 20mm across its length, you may need to shift the whole pattern along the datum to balance the cuts at both sides, then dry lay again to confirm. Move the pattern rather than squeezing the joints; a slightly uneven joint in herringbone is far more noticeable than in a straightforward grid, because the eye follows the zigzag.

Work outwards in one direction and keep checking

Herringbone locks together, so it rewards working in a controlled sequence. Start from the datum and work outwards in one direction, spreading only as much adhesive as you can comfortably cover in fifteen to twenty minutes. In warm rooms, that's less than you think.

• Use spacers consistently — 2mm or 3mm is typical for a rectified porcelain; wider joints suit rustic or handmade-looking tiles.
• At the T-junctions where a tile end meets a tile side, use a straight spacer rather than forcing a cross spacer into place.
• Check back to your datum lines every few courses with a tape measure, not just your eye.
• Use levelling clips on large-format tiles to keep the surface flat across the pattern.
• Back-butter large tiles and use a notched trowel that matches the tile size — a 10mm notch for most floor work, larger for big planks.

On timber floors, over underfloor heating, or anywhere the substrate moves, use a flexible adhesive and seriously consider an uncoupling membrane. Herringbone has more joints per square metre than a grid layout, and every one of them is a potential crack if the substrate shifts underneath.

Finishing touches that make the pattern sing

Leave the floor alone for at least 24 hours before grouting, or longer if the adhesive says so. When you do grout, work the float diagonally across the pattern rather than along it, and clean off as you go — herringbone joints are short and easy to overfill.

Grout colour is a design decision worth taking seriously. A grout matched closely to the tile lets the herringbone texture do the talking. A contrasting grout turns the pattern into a graphic statement, which suits a cloakroom or hallway but can overwhelm a large open-plan space. Whichever you choose, mix it consistently and keep the joints uniform — in a herringbone floor, consistency is what separates a professional finish from a decent attempt.