Tiling that does not crack or leak

Cue 1 Water passing through a grout line into an untanked wall over time.

AMARA 00:00 Start me with the thing people get most wrong.

NADIA 00:03 That a tiled shower is waterproof. It is not, and almost nobody knows it.

AMARA 00:09 The tiles are impervious though.

NADIA 00:11 The tiles are. The grout is not, and neither is the adhesive bed. Water goes through a grout line steadily and invisibly, and it has been doing it behind a lot of showers for years.

AMARA 00:25 So what actually keeps water out?

Cue 2 Tanking sequence: substrate, membrane, taped corners, pipe collars, then tile.

NADIA 00:27 The tanking behind the tiles. A liquid membrane or a bonded sheet system applied to the substrate before any tile goes on, with the corners taped and pipe penetrations sealed with collars.

AMARA 00:40 How far does it need to go?

NADIA 00:43 Beyond the bit that looks wet. Full height of the shower and at least the enclosure footprint plus a margin. In a wet room, the floor and the walls to a defined height across the whole room. Follow BS 5385 and the tanking manufacturer together, and if they disagree, that is a conversation to have before you start.

AMARA 01:06 What about plasterboard in a shower?

NADIA 01:08 It has no place there. Tile backer board, and then tank it anyway.

Cue 3 Floor deflection cracking a rigid tile, with span over 360 and 720 marked.

AMARA 01:14 Let us do floors. Why do floor tiles crack?

NADIA 01:17 Because a tile is a rigid brittle plate and the floor underneath it is not. Deflection is what kills floor tiles.

AMARA 01:26 How much movement is too much?

NADIA 01:28 The rule of thumb is span over 360 for ceramic, and span over 720 for natural stone, which is twice as demanding. Stone is stiffer and much less forgiving.

AMARA 01:40 Is there a site test?

Cue 4 Glass of water rippling on a bouncy floor.

NADIA 01:42 Walk on it. If you can feel it move, tiles will crack. Put a glass of water on the floor and have somebody walk past: if it ripples, you have a problem you need to fix before you tile, not a problem to mention afterwards.

AMARA 02:00 And the fix?

NADIA 02:01 Extra noggins, sistering the joists, overboarding with a proper tile backer rather than chipboard, or an uncoupling membrane where you genuinely cannot remove the movement. It is not preparation, it is the job.

AMARA 02:14 Adhesive. I have always just bought a tub.

NADIA 02:17 Then keep the tub for dry walls with small light tiles, and nothing else. Tub adhesive cures by drying, so behind a large impervious tile it may never fully cure at all.

Cue 5 Tile lifted to reveal voids behind, beside solid bed coverage.

AMARA 02:30 It just stays soft back there?

NADIA 02:32 It can, for a very long time. Powder cement based adhesive mixed with water for floors, wet areas, porcelain, stone and anything large or heavy. And flexible adhesive over anything that could move or has underfloor heating.

AMARA 02:47 How do I know I am getting enough adhesive behind the tile?

NADIA 02:52 Lift one occasionally and look. Everybody trowels the wall, presses the tile on, and assumes. In a wet area or on a floor you need close to solid bed coverage, because a void holds water and is where the tile cracks under a point load.

AMARA 03:10 Back buttering?

Cue 6 Grouted internal corner cracking, beside a siliconed one flexing.

NADIA 03:11 For large format tiles, yes. It is the difference between a floor that lasts and one where three tiles crack in the first winter.

AMARA 03:20 Last thing. Movement joints. I have never fitted one in my life.

NADIA 03:25 Almost nobody has, and it is the commonest avoidable defect in domestic tiling. Tiled surfaces expand and contract, and BS 5385 wants joints at the perimeter, over structural joints, at changes of background, and at intervals across large areas.

AMARA 03:41 What does that mean in a normal bathroom?

NADIA 03:44 Something very simple. Silicone every internal corner, silicone around the bath and the tray, leave a gap at the perimeter behind the trim, and do not grout tight into the wall to floor junction.

AMARA 03:58 And if I do grout it tight?

NADIA 04:00 You get that crack along the bottom of the wall that everybody has and nobody understands. Grout is rigid. Two planes that move relative to each other need something flexible between them, and that is what silicone is for.

Cue 1 Starting from a corner and drifting into a tapering cut at the far wall.

AMARA 04:16 Where do I start? A corner seems obvious.

NADIA 04:19 It is obvious and it is wrong, and it is the mistake that shows for twenty years. Rooms are not square. Start in a corner and the first row drifts, and by the far wall you have a tapering cut.

AMARA 04:35 So where?

NADIA 04:36 Find the centre, work outwards, then look at what the edge cuts become before you commit to anything.

AMARA 04:43 And if the edge cut is tiny?

Cue 2 Centre out setting, then shifted half a tile so both edge cuts are equal.

NADIA 04:46 Shift the whole layout by half a tile, so both ends get a decent cut. Two half tiles look deliberate. One full tile at one end and a twenty millimetre slip at the other looks like somebody made a mistake, because somebody did.

AMARA 05:03 Where should the cuts go?

NADIA 05:05 Where nobody looks. Behind the door, under the bath, at the bottom. And never at eye level on the wall you see first from the doorway.

AMARA 05:16 Do I start from the floor?

NADIA 05:18 Never. Fix a level batten and support the first full row on that. Floors are not level, and tiling off a floor puts the whole wall out of true by the time you reach the top.

Cue 3 Level batten supporting the first full row, bottom row cut last.

AMARA 05:32 So the bottom row?

NADIA 05:34 Cut last, once everything above has set. Take the batten off and fit the bottom row into whatever gap the floor has actually given you.

AMARA 05:44 Cutting. I have a manual cutter.

NADIA 05:46 Fine for straight cuts in ceramic. Porcelain is much harder and you will want a wet saw with a diamond blade, and you will be glad of it.

AMARA 05:58 Holes for pipes?

Cue 4 Wet cutting suppressing silica dust beside dry cutting indoors.

NADIA 05:59 Diamond hole saw with water. And for notches and curves, a grinder from the face, several shallow passes rather than one deep one.

AMARA 06:08 Is dust an issue with tile?

NADIA 06:10 A serious one. Tile and porcelain are high in silica, and cutting them dry indoors without extraction is one of the more damaging things done routinely on domestic jobs. Wet cutting is not about a neater cut, it is about your lungs.

AMARA 06:27 When can I grout?

NADIA 06:29 Once the adhesive has cured, which is usually at least twenty four hours and is printed on the bag. Grout too early and you trap moisture and solvent, and you get patchy colour you cannot correct afterwards.

Cue 5 Grout packed diagonally, then flooded and washed pale.

AMARA 06:44 How do I actually apply it?

NADIA 06:46 Diagonally across the joints with a rubber float, so it packs in rather than skimming over. Then remove the excess diagonally as well.

AMARA 06:55 Then sponge it?

NADIA 06:56 Damp sponge, rinsed frequently, in stages. And do not flood it, which is the commonest grouting fault there is.

AMARA 07:04 What does flooding do?

Cue 6 Grouted corner cracking beside a siliconed one flexing.

NADIA 07:06 Washes the cement out of the joint. You are left with a weak, pale, powdery line that looks wrong and fails early.

AMARA 07:14 There is always a haze afterwards.

NADIA 07:17 There is, and you polish it off dry with a cloth. People attack it with more water, which washes more cement out and makes it worse, so they add more water. It is a loop.

AMARA 07:31 Last thing. Corners.

NADIA 07:32 Silicone, never grout. Internal corners, wall to floor, around baths and trays and worktops, and the perimeter.

AMARA 07:39 Because they move.

NADIA 07:40 Two planes moving relative to each other, and grout is rigid. Grout hard into a corner and you get that crack along the bottom of the wall that is in every bathroom in the country.