Prepare a timber floor for tiling

Check your timber floor is solid, screw down loose boards, then overboard and joint it so tiles won't crack later.

AB-01Check the floor is ready for tilingWalk over the whole floor and feel for bounce or spring — any movement means the joists need extra support before you tile, because rigid tiles crack over flex. Check the joists are no more than 400mm apart centre to centre; wider than that and you'll need extra noggins first. Press on every board and replace any that feel soft, damp or rotten.

AB-02Clear the room and strip old flooringRemove furniture, carpet or vinyl, and lift the underlay and any tack strip and old nails. Sweep and vacuum the bare boards. If skirting is coming off to let the tile run to the wall, lever it away carefully so it can go back on afterwards. Fill any old nail holes with flexible wood filler so they don't show through the new board.

1 tube · Flexible wood filler

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AB-03Locate the joists and mark fixing linesFind the joists under the boards by looking for the line of existing nail or screw heads running across them, or use a stud detector on deep mode. Snap a chalk line along the centre of each joist right across the room so you know exactly where to screw later. Joists are usually at 400mm or 450mm centres, but always check rather than assume.

1 each · Chalk line

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1 each · Stud/joist detector

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AB-04Screw down every loose boardBefore you drill anything, find your stopcock (usually under the kitchen sink) and check it turns, so you can shut the water off fast if you hit a pipe. Pipes and cables can run anywhere under a timber floor, including diagonally, so use a detector but still assume something is there until you've proven otherwise. If in doubt, isolate the circuit at the consumer unit before drilling, and turn off the stopcock before cutting into anything that could hold water. Screw down every loose or bouncy board along the joist lines you marked, using 4x50mm countersunk wood screws every 300mm, and refix or punch down any raised nails.

1 box · Wood screws 4x50mm (box of 200)

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AB-05Cut and dry-lay the overboardChoose either 18mm WBP exterior-grade plywood or a cement-based tile backer board made for timber floors. Cut the sheets so the joints stagger like brickwork and never line up with the joints in the boards below. Dry-lay the whole floor first, leaving a 10mm gap around the room's edges for movement and a 3mm gap between boards, before you fix anything permanently.

4 sheet · WBP plywood sheet (2400x1200x18mm)

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AB-06Fix the overboard to the joistsScrew each sheet down into the joists themselves, not just into the boards below, at 150mm centres around the edges and 300mm centres in the field. Use screws long enough to bite at least 20mm into solid joist through the new board and the old flooring. Keep the same safety approach as before — expect a cable or pipe until you've checked. Countersink every screw head slightly so it doesn't sit above the surface.

1 box · Backer board screws 4x40mm (box of 100)

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AB-07Tape and fill the jointsCover every joint and screw head with flexible tile adhesive and press fibreglass jointing tape into it, then smooth it flat with a filling knife. Leave it to cure fully — check the tub, usually 24 hours — before you start tiling. This stops small movements at the joints cracking your finished tiles later.

1 tub (5kg) · Flexible tile adhesive

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1 roll · Fibreglass jointing tape

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AB-08Final check and tidy upOnce cured, run a spirit level across the whole floor and sand down any ridge higher than 2mm. Vacuum thoroughly so no grit is left under where the tiles will sit. Store any leftover screws and board offcuts, and dispose of packaging responsibly before you start tiling.

1 each · Sanding block

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