Most visual inspections of tiles use the sampling tables in ISO 2859-1. A common practice is general inspection level II, with zero tolerance for critical defects and AQLs such as 2.5 for major and 4.0 for minor defects. The right levels for you depend on your market and are set in your contract.
Laboratory tests are different. They follow the sampling rules in ISO 10545-1, which set how many tiles each test needs.
What AQL means
AQL stands for acceptance quality limit. It is the worst average defect level the sampling plan treats as acceptable. It is not a promise that the lot has that many defects or fewer.
In practice, you look up three things in the ISO 2859-1 tables. The lot size and inspection level give the sample size. The AQL then gives the acceptance number: the most defective units you can find in the sample and still accept the lot. Find one more and the lot fails.
Defects are sorted into classes before inspection. A critical defect makes the tile unsafe or unusable. A major defect means it would not be accepted by your customer. A minor defect is a small fault that would usually be tolerated. Each class has its own AQL.
Applying it to tiles
The awkward part with tiles is defining the unit. A lot is counted in boxes, but defects are found on single tiles. Agree in your contract which one you mean. These approaches are common:
- Treat the box as the unit, open the sample number of boxes, and count a box as defective if it holds more faulty tiles than your grade definition allows.
- Treat the tile as the unit, and inspect the sample number of tiles drawn from a spread of boxes.
- Use separate plans for visual grade, measurements and packing, since each check has its own sample size.
Write the rules down first
Whichever you choose, write down the defect classes, the unit, the inspection level and the AQLs before production starts. Then the inspector and the factory work to the same rule.
Lab test sampling
ISO 10545-1 deals with lots and samples for tile testing. It sets how many tiles to draw for each property, such as water absorption or breaking strength, and how to decide whether the lot conforms. Sample sizes depend on the test and, for some tests, on tile size.
Draw lab samples from your packed lot at the same visit as the visual inspection, and seal them. Our guide to tests to order before shipment lists the tests.
Choosing your levels
Tighter AQLs and higher inspection levels mean larger samples and stricter acceptance. They suit premium ranges and markets where customers reject small faults. Looser levels suit commercial grades where a few minor faults are expected. Your grade definition and your AQLs should match. A Premium order with a loose plan sends mixed signals.
The plan only works if the results are reported clearly. See what a tile pre-shipment inspection report should include.
Next step
We help you set defect classes, units and AQLs that fit your grade and market, and inspect to them. To agree your inspection plan, book a free sourcing review.