Procedure 03
Tiling quality checks
Finished tiling gets judged from 2 metres away by the client and from 200 millimetres away by the supervisor. Four measurements separate an opinion from a defect: the step across each joint, the width of each joint, the sound of the bed under a nylon rod, and the position of every movement joint.
01.How much lippage is allowed between two adjacent tiles?
Allowable tile lippage rises with joint width: 0.5 mm across joints under 3 mm, 1.0 mm across joints of 3 mm to 6 mm, and 2.0 mm across joints over 6 mm. Measure lippage with a feeler gauge under a 300 mm straight edge laid square across the joint.
A wider joint spreads the same step over a longer viewing distance, which is why the limit relaxes as the joint grows. Take a reading at the worst joint in each direction, at every joint that catches a fingernail dragged across the surface, and at four joints chosen at random per 10 square metres. A dial gauge replaces the feeler gauge where a dispute looks likely, because a dial gauge reads to 0.01 mm and prints a number that neither side can argue away.
Factory warpage counts as part of the measured step. A 600 mm square porcelain tile manufactured to a warpage allowance of 0.5 percent bows up to 4.2 mm along its 848 mm diagonal, while a rectified large format tile held to 0.2 percent bows about 1.7 mm. Check a suspect batch by laying four tiles face to face on a flat bench and reading the gap at the centre with a feeler gauge before blaming the tiler.
Table 1. Lippage limits by grout joint width
| Grout joint width (mm) | Maximum lippage (mm) | Typical application | Instrument and reference length (mm) |
|---|---|---|---|
| Under 3 | 0.5 | Rectified porcelain, internal wall tiling | Feeler gauge under a straight edge, 300 |
| 3 to 6 | 1.0 | Pressed ceramic on floors and walls | Feeler gauge under a straight edge, 300 |
| Over 6 | 2.0 | Extruded and handmade tile, external paving | Feeler gauge under a straight edge, 300 |
| Any width, tiles over 600 mm on any side | 1.0 | Large format porcelain, bond offset capped at 33 percent | Dial gauge reading to 0.01 mm |
Lippage limits apply to the finished tiled surface. A background outside the 3 mm limit on the plaster page makes the 0.5 mm and 1.0 mm rows physically unreachable, whatever the tiler does.
02.What is the minimum grout joint width for each tile type?
Minimum grout joint width measures 2 mm for rectified porcelain on an internal wall, 3 mm for an internal porcelain floor, and 6 mm for extruded tile, handmade tile and any external or wet floor. Read joint width with a joint gauge at five positions per wall, then record the narrowest and the widest of the five.
Joint width is a structural decision wearing a visual disguise. A grout joint absorbs the dimensional spread between tiles from one pallet, which reaches 1 mm on pressed ceramic and 0.3 mm on rectified porcelain, and the joint also lets the grout carry small thermal movement. Tiles pushed to a 1 mm joint absorb neither, so the first summer pushes a row of floor tiles into a ridge above the substrate.
Table 2. Minimum grout joint width by tile type and position
| Tile type and position | Minimum joint (mm) | Usual joint (mm) | Allowed variation along one row (mm) | Measured with |
|---|---|---|---|---|
| Rectified porcelain, internal wall | 2 | 2 to 3 | Plus or minus 0.5 | Joint gauge at 5 positions per wall |
| Pressed ceramic, internal wall | 2 | 3 | Plus or minus 1.0 | Joint gauge at 5 positions per wall |
| Porcelain, internal floor | 3 | 3 to 5 | Plus or minus 1.0 | Joint gauge at 5 positions per 10 square metres |
| Extruded or handmade tile, any position | 6 | 6 to 10 | Plus or minus 2.0 | Joint gauge at 5 positions per wall |
| Any tile, external or wet floor | 6 | 6 to 10 | Plus or minus 1.0 | Joint gauge at 5 positions per 10 square metres |
A joint that narrows from 3.0 mm to 1.5 mm along a single row of 10 tiles shows the setting out drifted by 15 mm across that row, and the cure is a reset rather than a wider grout bag.
03.How do you find hollow tiles by tapping?
A nylon tipped rod tapped on the four corners and the centre of a tile separates a dull knock from a light ring, and a ring means the adhesive bed lost contact with the tile or with the background. Tap every tile in wet rooms and circulation areas, and tap 1 tile in 5 on dry internal walls.
Confirm a suspect area by lifting one tile and measuring the contact area left on the back. Bed coverage of 95 percent applies to floors and wet areas, 100 percent applies to external work, and 80 percent applies to dry internal walls. Voids concentrated at one corner matter more than the same void area spread across the tile centre, because a corner void turns into a chipped edge the week the furniture arrives.
Ridges left standing from the notched trowel prove the tiler never collapsed the bed. Back buttering is the fix for any tile over 300 mm on either side, and back buttering adds roughly 1 mm to 2 mm to the bed thickness, which the tiler has to allow for at thresholds and at the junction with an existing floor.
Table 3. Bed coverage, tap sampling and trowel selection
| Location | Minimum bed coverage (percent of tile back) | Tiles tapped (proportion) | Trowel notch depth (mm) | Back buttering required above tile size (mm) |
|---|---|---|---|---|
| Dry internal wall, tiles up to 300 mm | 80 | 1 in 5 | 6 | 300 |
| Wet wall, shower and bath surround | 95 | Every tile | 8 | 300 |
| Internal floor, circulation and living space | 95 | Every tile | 10 | 300 |
| Internal floor over underfloor heating | 95 | Every tile | 10 to 12 | 300 |
| External paving, terrace and balcony | 100 | Every tile | 12 | 200 |
Coverage is measured on the back of a lifted tile as contact area divided by tile back area. Trowel notch depths are working selections and the adhesive data sheet overrides any figure in the notch column.
Reject the tiling when any line applies
- Lippage exceeds the Table 1 limit for the measured joint width at any joint
- Joint width varies along a single row by more than the Table 2 allowance
- Tapping finds a hollow tone at two or more corners of the same tile
- A lifted tile shows bed coverage below 95 percent in a wet area or on a floor
- Cut tiles narrower than half a tile width appear at a door opening or a focal wall
- A perimeter movement joint is grouted solid instead of filled with flexible sealant
- Grout shows shrinkage cracks, pinholes, or a colour step between mixing batches
- External corner tile edges are unmitred and carry no trim
- Movement joint spacing exceeds the Table 4 figure for that location
04.Where do movement joints go in a tiled floor or wall?
Movement joints run at 8 m to 10 m centres in an unheated internal tiled floor, tighten to 4 m to 5 m over underfloor heating or under direct sunlight, and tighten again to 3 m to 4 m on external paving. Every perimeter joint where tiling meets a wall measures 6 mm to 10 mm wide.
A movement joint runs through the full thickness of tile and adhesive, down to the substrate, and carries a flexible sealant instead of cement grout. A joint filled with grout at the perimeter is not a movement joint, whatever the drawing calls the line. Movement joints are the check most often skipped on a fit out, and the omission stays invisible until a floor tents up along one wall in the second summer.
Table 4. Movement joint spacing and width by location
| Location | Maximum spacing in each direction (m) | Joint width (mm) | Joint depth | Filled with |
|---|---|---|---|---|
| Internal floor, no heating, no direct sun | 8 to 10 | 6 to 10 | Full tile plus full adhesive, down to the substrate | Flexible sealant on a backer rod |
| Internal floor over underfloor heating | 4 to 5 | 8 to 10 | Full tile plus full adhesive, down to the substrate | Flexible sealant on a backer rod |
| Internal floor under direct sun, atrium or glazed wall | 4 to 5 | 8 to 10 | Full tile plus full adhesive, down to the substrate | Flexible sealant on a backer rod |
| External paving, terrace and balcony | 3 to 4 | 10 | Full tile plus full adhesive, down to the substrate | Flexible sealant rated for movement of 25 percent |
| Internal wall tiling | 3 to 4.5 | 6 | Full tile plus full adhesive, down to the background | Flexible sealant or a proprietary joint profile |
| Perimeter at a wall, column or door frame | Every occurrence | 6 to 10 | Full tile plus full adhesive | Flexible sealant on a bond breaker tape |
| Structural movement joint in the slab | Every occurrence | Same width as the structural joint | Full depth, continuous, no change of line | Proprietary movement joint profile |
Add a joint at every change of substrate, at every doorway, and at the junction between wall tiling and floor tiling, regardless of the spacing figures above. Spacing is measured centre to centre with a steel tape on the finished setting out.
05.How should a tiling defect be recorded?
A tiling defect entry records the tile position by row and column counted from a fixed corner, the measured value with the instrument used, and the limit that the value missed. Row 4 from the floor, column 7 from the door reveal, 1.8 mm lippage under a 300 mm straight edge against a 1.0 mm limit.
Counting rows and columns from a fixed corner survives the moment when the marker tape falls off the wall overnight. Photograph the defect with the joint gauge or feeler blade still in place and a numbered marker card showing the room reference, then send the entry to the register described on the punch list page with a target date and a named trade.
Group the tiling entries by trade before issuing the register. A tiler asked to return once for 14 items prices one visit. The same 14 items sent as separate messages over two weeks produce four visits, and the fourth visit never happens. Grouping also exposes a pattern that a scattered list hides: 11 lippage entries along one wall point at a background outside 3 mm under a 2 m edge rather than at the tiler.