Prepare a concrete floor for tiling

Check, repair, level and prime a concrete floor so it's flat, dry and ready for tiling.

FL-01Clear the room and inspect the floorRemove furniture, carpet, underlay, or old flooring right back to the bare concrete. Scrape off old adhesive or paint with a floor scraper. Sweep and vacuum thoroughly, then look over the whole floor for cracks, loose patches, or areas that look uneven.

1 each · Floor scraper

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1 each · Stiff broom

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1 each · Wet/dry vacuum cleaner

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FL-02Test the floor for dampUse a moisture meter on the bare concrete, especially if the slab is new, in a ground-floor room, or you've had damp problems before. If it reads damp, fit a liquid damp-proof membrane (DPM) over the whole floor and let it cure fully before continuing - tiling over a damp slab pushes tiles off later. Skip this step if the floor is old, dry, and has never had a damp issue.

1 each · Digital moisture meter

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1 5kg tub · Liquid DPM (damp-proof membrane)

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FL-03Repair cracks, holes and hollow patchesTap the floor with a hammer handle - a hollow, drummy sound means the surface has come loose from the slab below and needs breaking out and re-filling, not just skimming over. Chase out cracks slightly with a bolster, clear the dust, then push in a flexible repair filler and smooth level with a trowel. Leave to cure fully, usually 24 hours, before you check the level.

1 2kg tub · Flexible crack repair filler

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1 each · Bolster chisel

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1 each · Trowel

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FL-04Check the floor for levelLay a long straightedge or spirit level across the room in several directions and mark any high or low spots with chalk. Tiles need a flat base - more than about 3mm of variation under a 1m level generally needs correcting before you tile, or you'll get lippage between tiles.

1 each · 2m aluminium straightedge

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1 each · Chalk line

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FL-05Grind down high spotsUse an angle grinder fitted with a diamond cup wheel to take down high spots and any remaining adhesive residue. Wear an FFP3 dust mask, safety glasses and ear defenders - concrete dust is fine and gets everywhere. Before you grind or cut into the slab, check whether there's underfloor heating pipework or electric mats below, especially near the edges of rooms or under old tiled areas - use a detector but still treat the floor as if something's there until you've proved otherwise. If there's any doubt, isolate underfloor heating at the manifold or consumer unit first, and know where your stopcock is (usually under the kitchen sink) so you can shut the water off fast if you do hit a pipe. Vacuum thoroughly once you've finished.

1 each · Diamond cup wheel for angle grinder

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1 pack of 5 · FFP3 dust mask

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1 each · Safety glasses

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1 each · Ear defenders

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FL-06Prime the floorRoll on a concrete floor primer, diluted as the manufacturer instructs, covering the whole area evenly. This helps self-levelling compound or tile adhesive bond properly, and stops the concrete pulling moisture out of them too fast. Let it dry fully - usually 1 to 4 hours - before doing anything else.

1 5L · Concrete floor primer

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1 each · Paint roller and tray

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FL-07Apply self-levelling compound if neededIf step FL-04 found more than about 3mm of unevenness, mix self-levelling compound following the bag instructions and pour it onto the primed floor. Spread it with a levelling rake, working quickly - it starts setting within minutes. Skip this step if the floor was already flat.

1 20kg bag · Self-levelling compound

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1 each · Levelling rake/spreader

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1 each · Mixing paddle for drill

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FL-08Leave the floor to cureLeave the floor completely undisturbed while it cures - check the product packaging, but self-levelling compound usually needs 24 to 48 hours before you can walk on it, and longer before tiling. Keep the room ventilated but away from direct heat or strong draughts, which can make the surface dry too fast and crack.

FL-09Final check before tilingOnce cured, run a straightedge over the floor again to confirm it's flat, and check it's fully dry before covering it. Sweep and vacuum any dust off the surface - dust left under tile adhesive weakens the bond. The floor is now ready for tiling.

FL-10Clean up and dispose of wasteBag up old flooring, adhesive scrapings and rubble. Check your local council's rules before putting rubble or large amounts of waste in a general waste bin - many councils have limits or a separate collection for building waste. Rinse tools before the primer or compound dries on them, and reseal any leftover materials for next time.

3 each · Heavy-duty rubble sacks

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