Floor tiling

Typical jobs

• Porcelain through a hallway and kitchen on a concrete floor
• Overboarding a suspended timber floor before laying ceramic tiles
• Levelling an uneven floor with a self-levelling compound first
• Movement joints round the edge of a large open-plan floor
• Laying tiles over a new electric underfloor heating mat
• Replacing a cracked tile floor in a hallway, lifting the old tiles and adhesive first
• Ceramic floor tiles in a downstairs cloakroom with light traffic

The floor under the tiles matters more than the tiles. An existing concrete or sand and cement floor that is dry, flat and sound can be tiled once it is primed, where the adhesive maker asks for that. New bases need time: BS 5385-3 allows at least three weeks for a new sand and cement screed and about six weeks for new concrete. A calcium sulphate (anhydrite) screed must be dry to 0.5% moisture or less, have its surface skin sanded off and be primed, because cement-based adhesive reacts with it. A suspended timber floor moves as you walk on it, and a tiled floor must be rigid. It is usually overboarded with exterior plywood or tile backer board at least 15 mm thick, screwed at about 300 mm centres, and a decoupling membrane can go on top. Skip that step and the grout cracks, then the tiles.

Flatness comes next. A common working limit is about 3 mm under a 2 m straightedge, tighter for large format tiles, which show every dip, so a tiler may pour a self-levelling compound before laying, and that is a separate cost and a day's drying. Tiles are bedded in a solid layer of adhesive, not on dabs, so there are no hollow spots to crack under a chair leg. Porcelain, large format tiles, heated floors and timber bases usually call for an improved, deformable adhesive, classed C2 and S1 under BS EN 12004. BS 5385-3 is the British Standard for floor tiling, and it asks for movement joints: a flexible gap round the edge of the room and, on larger floors or across door thresholds and changes in the base, joints within the floor itself. A floor tiled tight to the walls with no edge gap is one of the commonest reasons for tiles lifting in a ridge.

Porcelain is the usual choice for hallways and kitchens because it is dense and hard-wearing; ceramic suits lighter use. For anywhere that gets wet, check the slip rating: a pendulum test value (PTV) of 36 or more counts as low slip potential in HSE and UK Slip Resistance Group guidance. Think about door heights too: tile, adhesive and any overboarding together raise the floor, and doors may need trimming. The floor is the last thing in the room to be tiled and the first thing people will walk on, so leave it alone for at least a day after grouting.

Which floor tile suits which room comes down to wear, water and grit. Porcelain is fired dense and takes in very little water, so it works in kitchens, hallways and bathrooms alike, and through-body porcelain hides chips because the colour runs all the way through. Ceramic floor tiles are softer and cheaper, and fine in a cloakroom or a bathroom with light use, as long as the maker rates them for floors. Natural stone such as slate, limestone and travertine needs sealing and a stiffer base, and is covered under natural stone tiling. In a kitchen, look for stain resistance and a grout colour that hides spills. In a hallway, grit carried in from outside scratches polished finishes, so matt or textured tiles and a sunken doormat last longer. In a bathroom, grip when wet comes first. Laying itself starts from a line set out from the middle of the room or the main doorway, so the cut tiles at the edges come out even.

Most floor failures start in the base, so the useful questions are about what happens before the first tile goes down.

• What will you do to the floor first: overboard, membrane, prime or level? Is that in the price?
• Where will the movement joints go, round the edges and across doorways?
• Do you bed every tile in solid adhesive, and which adhesive class?
• On a timber floor, which board, how thick, and how is it screwed down?
• Are door trimming and thresholds included, and when can we walk on it?

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