Ceramic wall tiles normally have water absorption above 10%, measured by weight. Under ISO 13006 and EN 14411, that places them in group BIII, the group for porous dry-pressed tiles, which is covered by Annex L of EN 14411.
High absorption is not a defect in a wall tile. It is a property of the porous body, and the glaze on the face is what keeps water out in use.
What water absorption measures
Water absorption is the weight of water a fired tile takes up, as a percentage of its dry weight. The test method is ISO 10545-3. Tiles are dried, weighed, soaked in boiling water or under vacuum, and weighed again.
The figure tells you how dense the body is. Porcelain tiles are at 0.5% or less. Ceramic floor tiles often sit between 3% and 10%. Wall tiles sit above 10%. The full scale of groups is in what water absorption makes a tile vitrified.
Why high absorption suits walls
- The porous body is lighter, which makes tiles easier to fix to a wall.
- Porous tiles are easy to cut with a hand cutter.
- The open back gives cement-based adhesive a good grip.
- The body fires at a lower temperature than porcelain, which helps keep production cost down.
Where it becomes a problem
A porous body expands slightly as it takes up moisture over time. If the glaze cannot follow that movement, fine cracks called crazing can appear in the glaze. This is why glazed wall tiles should also have a crazing-resistance test to ISO 10545-11. The test is described in crazing in wall tiles.
Water that enters a porous body can freeze and crack the tile. Ceramic wall tiles are therefore for indoor use, or outdoor use only in climates without frost. They are also not suitable for floors, swimming pools or wet exterior areas.
Very high absorption can also point to an under-fired or weak body. A report that shows a much higher value than the factory's usual figure is worth a question.
How to read the test report
Ask for a recent ISO 10545-3 report from an accredited laboratory, for the product you are buying. Check these points:
- The report gives an average value and individual values for the tiles tested.
- The group stated on the report matches what the factory claims, usually BIII for wall tiles.
- The product name, size and plant on the report match your order.
- The report is recent, since body recipes can change.
Breaking strength sits on the same report. For BIII tiles, EN 14411 Annex L sets a higher minimum for tiles 7.5 mm or thicker than for thinner ones, so check the thickness alongside it. Our guide on reading a lab certificate shows what else to look for.
Next step
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