You can check wall tiles for warpage with three simple tools: a steel straightedge, a set of feeler gauges and a flat surface. Check edges and diagonals on tiles from several boxes, measure the gaps, and compare the results with the factory's declared tolerance.
Laboratories measure flatness to ISO 10545-2 with a dial gauge rig, and EN 14411 sets the limits. The on-site method below is a practical screen. It tells you whether a lot is clearly fine or needs a laboratory check. The background on what flatness means is in how flat a floor tile should be.
What you are looking for
- Centre curvature: the middle of the tile is higher or lower than the corners, so the tile is bowed or dished.
- Edge curvature: an edge is curved along its length instead of straight.
- Warp: one corner is out of plane with the other three, so the tile rocks on a flat surface.
On a wall, these faults show as lippage, where one tile edge sits proud of its neighbour. Gloss glazes and side light make lippage very visible, and larger formats show it more.
The checks, step by step
- Take tiles from several boxes chosen at random, from different pallets, not just the top of one stack.
- Lay a tile face up on a flat surface such as a granite table or a sheet of float glass, and press each corner to see if it rocks.
- Place the straightedge along each edge and across both diagonals on the glazed face.
- Slide feeler gauges into the largest gap under the straightedge and note the thickness that just fits.
- Place two tiles face to face and look for rocking or an even gap around the edges, which shows a bowed pair.
- Lay six to eight tiles together on the floor, with spacers, and look along the surface for lippage.
Reading the results
EN 14411 expresses flatness limits as a percentage of the tile's dimension, and the limits differ by group and by whether the tile is rectified. Ask the factory for its declared tolerance for your product, and convert the percentage into millimetres for your size.
The arithmetic is simple. A 300x600 mm tile has a diagonal of about 671 mm, so a limit of 0.3% on the diagonal would be about 2 mm. Use the real limit from the factory's declaration or test report, not this example.
If several tiles are close to or beyond the limit, send a sample to an accredited laboratory for an ISO 10545-2 test before loading. Our guide on reading a lab certificate shows how to check the report.
Common mistakes
- Measuring over the back ribs instead of on the face.
- Checking only the sample board tiles, not production boxes.
- Mixing calibres, which makes size differences look like warpage on a laid-out panel.
- Using a wooden or aluminium rule that is itself not straight.
Next step
We check flatness on production tiles at the factory and send samples for laboratory tests where results are close to the limit. To add this to your inspection, book a free sourcing review.