Lay natural stone floor tiles on a timber floor — HomeGraft

Overlay your timber floor with a rigid board, then lay and grout natural stone tiles safely and level.

SF-01Clear the room and check the floorTake up any old flooring and skirting boards you plan to replace, and clear the room completely. Check the joists run at roughly 400-600mm centres, and walk over the whole floor to feel for bounce or soft spots. Note the room's length and width in mm so you can work out how much board and stone you need, adding 10% extra for cuts and breakages.

2 each · Dust sheets

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SF-02Find pipes, cables and your stopcock before you drillCables and pipes can run under a timber floor in places you don't expect, especially where boards have been lifted before for wiring or plumbing. Use a cable and pipe detector to scan the area you're about to screw into, but treat every hole as if something could be there — detectors miss deep cables, pipes in cavities, and anything behind old metal mesh or foil-backed material. Find your stopcock (usually under the kitchen sink) and check it turns freely, so you can shut the water off fast if you hit a pipe. If you have any doubt at all, isolate the relevant circuit at the consumer unit before drilling, and turn the water off at the stopcock before cutting into anything that could carry water.

1 each · Cable and pipe detector

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SF-03Strengthen bouncy joists or loose boardsScrew down any loose or squeaking boards with 4.5x50mm screws driven into the joist below, not just into the board. If the floor flexes noticeably, add extra noggins between joists at 400mm centres to stiffen it — natural stone is rigid and will crack over a floor that moves. Skip this step if the floor already feels solid underfoot.

6 each · Timber noggins (47x100mm)

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1 box · Floor screws (4.5x50mm, box of 200)

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SF-04Fit a rigid overlay board over the timber floorScrew 18mm WBP plywood sheets down across the whole floor, staggering the joints like brickwork so no two sheets line up. Fix every 150mm around the edges and every 300mm across the middle of each sheet, screwing into the joists below, and leave a 10mm gap at the walls for movement. This rigid layer stops the timber floor flexing under the stone tiles, which are far less forgiving than ceramic.

3 sheet · 18mm WBP plywood sheet (1220x2440mm)

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1 box · Floor screws (4.5x50mm, box of 200)

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SF-05Tape and seal the board jointsRun fibreglass jointing tape over every seam between plywood sheets, then smooth a thin layer of flexible tile adhesive over the tape with a filling knife. Let this cure fully before you carry on — usually overnight. This stops movement at the joints from cracking the grout lines above.

1 roll · Fibreglass jointing tape (50mm x 45m)

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1 kg · Flexible tile adhesive (for jointing)

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SF-06Plan your tile layoutDry-lay a row of tiles across the room in both directions to see how the cuts fall at the walls, and adjust your starting point so you don't end up with slivers of stone at one edge. Mark a straight guide line on the board with a chalk line, starting from the most visible doorway or focal wall. Natural stone tiles vary slightly in size, so mix tiles from several boxes as you go for an even look.

SF-07Mix and spread flexible tile adhesiveMix a flexible, rapid-set C2 S1 adhesive rated for natural stone, following the bag's water ratio exactly. Spread it with a notched trowel — a 10mm notch works well for most stone tiles — combing it in one direction so air can escape as you lay each tile. Only spread enough for 20-30 minutes' work, as flexible adhesive skins over quickly.

4 bag · Flexible C2 S1 tile adhesive (20kg bag)

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1 each · Notched trowel (10mm)

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SF-08Lay the first row of stone tilesPress each tile down with a slight twisting motion, then tap it level with a rubber mallet, checking across neighbouring tiles with a long straight edge. Use 3mm spacers between stone tiles, as natural stone needs a wider joint than ceramic to allow for its uneven edges. Work in small sections and check levels constantly, since a lippy stone floor is hard to fix later.

1 m² · Natural stone floor tiles (e.g. travertine, limestone)

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1 box · Tile spacers (3mm, box of 250)

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SF-09Cut tiles to fit edges and obstaclesMost natural stone is too hard and brittle for a manual tile cutter, so use a wet tile saw or an angle grinder fitted with a diamond blade rated for stone. Cut outdoors or over a tray if possible, as wet-cutting stone makes a lot of slurry. Measure each cut individually rather than assuming tiles are identical, since natural stone sizes can vary by a few millimetres.

1 each · Diamond wet-cutting blade (for angle grinder/tile saw)

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SF-10Leave the floor to cure before groutingLeave the tiled floor untouched for at least 24 hours, or longer in a cold room, before you walk on it or start grouting. Check the adhesive manufacturer's instructions, as some rapid-set products cure faster. Keep pets and children out of the room during this time.

SF-11Seal the stone before groutingMany natural stones — travertine, limestone, slate and sandstone especially — are porous and will stain permanently if grout gets into the surface. Wipe on an impregnating stone sealer with a clean cloth, following the tin's coverage rate, and let it dry fully before grouting. Skip this step only if your supplier confirms the stone is pre-sealed or naturally non-porous, such as some slates.

1 each · Impregnating stone sealer (1L)

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SF-12Grout the jointsPush a flexible, wide-joint grout into the gaps with a rubber grout float, working diagonally across the joints so you don't drag grout back out. Wipe off the excess with a damp sponge before it hardens, rinsing the sponge often. Leave the grout to cure for the time stated on the bag before walking on it normally.

1 bag · Flexible wide-joint grout (5kg)

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1 each · Grout sponge

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SF-13Clean up and apply the final sealOnce the grout has fully cured, buff off any remaining haze with a dry cloth, then apply a second coat of stone sealer over the whole floor including the grout lines. Run a bead of colour-matched silicone sealant where the floor meets the skirting, instead of grout, to allow for movement. Clear away all offcuts, dust and packaging, and vacuum the room before moving furniture back in.

1 each · Impregnating stone sealer (1L)

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1 tube · Colour-matched silicone sealant (300ml)

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