A supplier says the defect rate is below 1%. On a 300 m² order that sounds like three square metres — but the number your client sees is panels, not square metres, and the two do not convert the way most buyers assume. A standard 1200 × 600 mm panel covers 0.72 m², so 300 m² is about 417 panels, and 1% of the panel count is about four panels. Whether four is acceptable depends on what counts as a defect, how the sample was drawn, and what the purchase order says. This guide works through the arithmetic, the sampling logic, and the wording that makes the claim enforceable.
How many panels are in a 300 m² order?
The conversion is straightforward once you know the panel format. A 1200 × 600 mm sheet covers 1.2 × 0.6 = 0.72 m². Divide the order area by that number and round up, because you cannot buy a fraction of a panel.
| Format | Area per panel | Panels in 300 m² |
|---|---|---|
| 1200 × 600 mm (standard) | 0.72 m² | 417 |
| 1200 × 2900 mm (large format) | 3.48 m² | 87 |
Two details change the count. First, the order area usually includes a waste allowance, so the purchased area is higher than the installed area; the panel count should be based on what you buy, not what ends up on the wall. Second, a wall with many openings or a strong pattern match may need more material, which raises the panel count again. The 417 figure is the baseline for a simple 300 m² order with no waste allowance.
Does “below 1%” mean area or panel count?
The two readings give similar numbers but different conversations. One percent of 300 m² is 3 m². One percent of 417 panels is about 4.17 panels. Four panels at 0.72 m² each is 2.88 m², so a four-panel defect count is roughly consistent with the 3 m² area reading.
The readings diverge when defects are concentrated. One panel with a large area of surface damage can be 0.7 m² of defective material but only one panel; four panels with small edge chips can be four defects but a small fraction of a square metre. If the contract does not say whether the rate is measured per panel or per square metre, both sides can be right and the argument has no resolution.
There is a second ambiguity: “below 1%” is an upper bound, not a prediction. A batch can be at 0%, at 0.4%, or at 0.9% and still satisfy the sentence. The buyer’s protection is not the number; it is the inspection and the remedy written into the order.
What counts as a defect?
A defect rate without a definition is a marketing number. For flexible stone, separate the categories before you discuss percentages.
- Functional defects. Delamination between the stone face and the backing, a crack through the sheet, backing separation at a cut edge, thickness or weight outside the declared band, or a panel that fails the agreed bend test. These affect performance and should not be installed.
- Cosmetic defects. Edge chips, surface marks, colour outside the approved sample range, or pattern misregistration. Some are acceptable if they fall on a cut edge or in a concealed area; others are not.
- Packaging defects. Crushed corners, wet packs, or missing batch labels. These are acceptance items in their own right, not part of the panel defect rate.
The acceptance criteria should be written per property: thickness band, weight band, minimum bend radius, mesh coverage, colour against the retained sample, edge condition, and packaging. A panel that meets every criterion is not a defect even if it looks different from its neighbour; natural variation is expected within the approved range.
Does the defect rate apply to my shipment or to the whole production run?
This is the question most buyers never ask, and it changes what the number means. A factory’s “below 1%” is usually measured across a production period — a month, a quarter, or a rolling average — not on the specific lot that goes into your container. A run of 10,000 m² at 0.8% can still produce a container with a cluster of defects, because defects tend to concentrate around a shift, a pigment lot, or a machine adjustment rather than spreading evenly.
Ask whether the rate is per batch or a company average, and ask for the defect count recorded for your batch. A supplier that tracks real numbers can answer; a supplier that only has a brochure figure will not. If the number is an average, treat it as context, not as an acceptance criterion — your protection is the sampling plan and the remedy, not the average.
The COA describes the batch, but it does not usually report the defect distribution. That is another reason to inspect the actual panels rather than rely on a document that was written before the container was packed.
Un échantillon peut-il prouver un taux de défauts inférieur à 11 TP3T ?
Habituellement non, et l'arithmétique en est la raison. Si vous inspectez 50 panneaux et ne trouvez aucun défaut, une règle statistique standard (souvent appelée règle des trois) place la borne supérieure de confiance à 951 TP3T à environ 61 TP3T. Ne trouver aucun défaut dans 50 unités ne prouve pas que le taux est inférieur à 11 TP3T ; cela montre seulement qu'il est peu probable que le taux dépasse environ 61 TP3T.
Pour bornrer le taux en dessous de 11 TP3T avec zéro défaut au niveau de confiance de 951 TP3T, il faut inspecter environ 300 panneaux, soit la majeure partie d'une commande de 417 panneaux. L'inspection de 100 panneaux donne une borne supérieure d'environ 31 TP3T. Un échantillon de 80 panneaux donne environ 3,751 TP3T. Plus l'échantillon est petit, plus l'allégation est faible.
C'est pourquoi un plan d'échantillonnage compte plus que le chiffre annoncé. Le plan définit la taille de l'échantillon, le nombre d'acceptation et les risques acceptés par les deux parties. Le Référence NIST/SEMATECH sur l'échantillonnage d'acceptation explique la logique ; les chiffres adaptés à votre commande doivent être convenus avec le fournisseur, et non copiés depuis un tableau générique.
Quel plan d'échantillonnage dois-je convenir avant la production ?
Un plan praticable répond à cinq questions : qu'est-ce que le lot, combien de panneaux sont échantillonnés, combien de défauts sont autorisés, que se passe-t-il si la limite est dépassée, et qui inspecte. Le tableau ci-dessous montre la forme du plan ; les valeurs sont un exemple à discuter, et non une norme recommandée.
| Élément | Exemple | Why it matters |
|---|---|---|
| Taille du lot | 417 panneaux | Définit la population à laquelle le taux s'applique |
| Taille de l'échantillon | 80 panneaux, prélevés au hasard sur les palettes | Le prélèvement aléatoire empêche la “ palette dorée ” |
| Acceptance number | 1 defect allowed | Sets the pass/fail line before inspection |
| Rejection number | 2 or more defects | Entraîne un tri, une remise en état ou une réinspection |
| Inspecteur | QC usine plus représentant de l'acheteur ou partie tierce | Sépare la partie ayant un intérêt de la décision |
Si le produit est un mur d'accentuation ou un lobby d'hôtel où chaque panneau est visible, envisagez l'inspection 100% au lieu de l'échantillonnage. Elle est plus lente et plus coûteuse, mais c'est le seul moyen de connaître le décompte réel plutôt qu'une borne de confiance.
Comment rédiger la clause de défaut dans le bon de commande ?
La clause doit rendre la réclamation testable. Une structure pratique :
- Unité. Précisez si le taux est par panneau ou par mètre carré, et si un panneau avec plusieurs défauts compte une ou plusieurs fois.
- Définitions. Listez les défauts fonctionnels, cosmétiques et d'emballage, avec les critères d'acceptation pour chaque propriété.
- Échantillonnage. Indiquez la taille de l'échantillon, le nombre d'acceptation, la méthode de dessin et le point d'inspection (avant expédition).
- Remède. Dites ce qui se passe lorsque la limite est dépassée : tri et remplacement, remise en état, réinspection, crédit ou rejet du lot.
- Evidence. Require photographs, panel IDs, batch numbers, and the inspection report with the shipment.
- Timing. Set the deadline for a claim and the point at which the buyer is deemed to have accepted the shipment.
Our declared defect rate is below 1%, and the batch record and COA travel with the shipment. The clause is what turns that declaration into something the buyer can verify and enforce.
What do I do when the count exceeds the claim?
Hold the affected panels, document them, and classify the defects before deciding the remedy. If the defects are cosmetic and isolated, a sort and replacement of the affected panels is usually faster than rejecting the lot. If they are functional or spread across the batch, the lot should be re-inspected or replaced. The inspection failure recovery plan covers the sequence in detail, and the batch consistency check shows how to compare the replacement against the approved sample.
The worst outcome is installing the defective panels to keep the schedule and negotiating afterwards. Once the wall is up, the remedy is no longer a sort; it is a removal. If you are still specifying the order, the gamme de parements en pierre flexible lists the panel formats and thickness bands that determine the panel count.
FAQ
Is a below-1% defect rate a guarantee?
No. It is a declared rate for a production run. The enforceable protection is the acceptance criteria and the remedy in the purchase order, backed by an inspection before shipment.
Does 1% mean 3 m² or 4 panels?
Both readings are possible. By area, 1% of 300 m² is 3 m². By panel count, 1% of 417 panels is about 4.17 panels. The contract should state which unit applies.
Can I inspect every panel?
Yes. For a visible feature wall or a high-value project, 100% inspection is the only way to know the actual defect count rather than a statistical bound. It adds time before shipment.
What sample size proves a rate below 1%?
With zero defects and 95% confidence, roughly 300 panels. Smaller samples can only bound a higher rate — about 6% for 50 panels, about 3% for 100 panels.
Should I reject the whole lot for four defective panels?
Usually not, if the defects are cosmetic and isolated. Sort and replace the affected panels, re-inspect, and document the result. Reject the lot when the defects are functional or spread across the batch.
Does the defect rate include packaging damage?
It should be a separate acceptance item. Crushed corners, wet packs, and missing labels are packaging defects and should have their own criteria and remedy.
