Crazing is a network of fine hairline cracks in the glaze of a tile. The cracks stay in the glaze layer and do not go through the body. They often look like a spider's web and show up most when dirt or grout gets into them.
The test for it is ISO 10545-11. Tiles are exposed to high-pressure steam in an autoclave, then a stain is applied to the glaze to reveal any cracks. EN 14411 calls for crazing resistance on glazed tiles.
Why wall tiles craze
Crazing happens when the glaze is under tension. The glaze and the body expand and contract by different amounts with heat and moisture. When the body grows more than the glaze can follow, the glaze cracks.
Porous ceramic wall tiles are more exposed to this than porcelain. Their body slowly takes up moisture from the air and the adhesive and expands slightly over months or years. This moisture expansion can be measured with ISO 10545-10. It is also why crazing can appear long after a wall is finished. The link between absorption and crazing is explained in what water absorption ceramic wall tiles have.
- A poor match between glaze and body expansion, from the glaze recipe or body mix.
- Under-firing, which leaves a weaker, more porous body.
- Too thick a glaze layer in some areas.
- Moisture uptake by the body over time.
- Heat stress in use, such as behind a hob.
How the ISO 10545-11 test works
Whole tiles are placed in an autoclave and exposed to steam under pressure for a set time. The steam forces moisture into the body quickly, which imitates years of slow expansion in a short test. After cooling, a stain is brushed on the glaze and wiped off. Any crazes hold the stain and become visible.
A passed test means no crazes were seen on the tested tiles. It does not guarantee every tile from every batch, so ask for a recent report on the product you are buying, and order a fresh test on your lot if the order is large.
Crazing as a design feature
Some tiles have a deliberate crackle glaze, made to look old or handmade. ISO 10545-11 excludes products where crazing is an intended decorative feature. If you sell such a tile, label it clearly, because customers may otherwise treat the crackle as a defect.
What to do as an importer
- Ask for an ISO 10545-11 report from an accredited laboratory for each wall tile range.
- Check that the report names the same product, size and plant as your order.
- Have a sample from your production lot tested if the range is new or the order is large.
- Keep a few tiles from each batch, so you can test them if a complaint comes in later.
Crazing is one of several defects to watch for in wall tiles; the others are listed in common defects in wall tiles. Our guide on reading a lab certificate helps you check the report itself.
Next step
We collect crazing reports, arrange independent tests on your lot and keep retained samples from each batch. To set this up, book a free sourcing review.