# Tiling that does not crack or leak

*Deflection, tanking and movement joints: the three things that decide whether tiling lasts.*

## Production summary

- Modules to record: 2
- Total script: 1186 words, about 8 minutes of finished audio
- Voices: Amara (host) and Nadia (practice educator)
- Level: Beginner to competent DIY

## Accreditation wording that must appear in the description

- **The CPD Certification Service** (planned): Application scheduled.
- **BS 5385** (aligned): Written against the British Standard for wall and floor tiling. Alignment is our own mapping and implies no endorsement.

> Do not upgrade any of these words in a description or a thumbnail. Aligned is not accredited, and planned is not approved.


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## Substrates, deflection and tanking a wet area

**Runtime** about 4 minutes. **Words** 641. **Starts at** 00:00 in the full course recording.

### Learning outcomes to state on camera

- Assess a substrate for flatness, stability and deflection
- Explain why tiles crack over a floor that moves
- Tank a shower or wet room correctly and know where tanking must extend
- Choose adhesive and grout appropriate to the situation

### Script


`[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.

### Sources for the on screen credit

- BS 5385, wall and floor tiling, British Standards Institution
- Tiling to wet areas and tanking guidance, The Tile Association
- Substrate preparation and deflection limits, The Tile Association

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## Setting out, cutting and grouting

**Runtime** about 4 minutes. **Words** 545. **Starts at** 04:16 in the full course recording.

### Learning outcomes to state on camera

- Set out a wall or floor so the cuts fall where they look right
- Cut tiles accurately, including holes and mitres
- Grout and finish without staining or cracking
- Seal junctions correctly with silicone

### Script


`[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.

### Sources for the on screen credit

- BS 5385, wall and floor tiling, British Standards Institution
- Setting out and grouting good practice, The Tile Association
- Control of silica dust in construction, Health and Safety Executive

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