What is a 'lot' as per IS 8920?

A lot is defined as a collection of tiles of the same type, size, and grade from a single source of manufacture, submitted for inspection at one time (Clause 2.2).

How many tiles do I need to inspect visually for a lot of 5,000 tiles?

For a lot size between 2001 and 10000, you need to select a sample of 80 tiles for visual inspection (Table 1).

How many tiles are allowed to be defective in a visual inspection sample of 80 tiles?

For a sample size of 80, the lot is considered satisfactory if the number of defective tiles does not exceed 7 (Table 2).

How many samples are taken for physical tests like water absorption?

For every 20,000 tiles or part thereof in the lot, a sample of 5 tiles is selected for physical tests (Table 3).

IS 8920

: 1978

Methods for sampling burnt clay tiles

CurrentSpecializedTesting MethodMaterials Science · Clay and Stabilized Soil Products

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This standard lays down the procedure for sampling burnt clay tiles to ascertain their conformity to a given specification. It covers terminology, the scale of sampling for visual and physical characteristics, the method of selecting samples, and the criteria for conformity.

Methods for sampling burnt clay tiles

Quick Reference Values

Sample size for visual inspection (Lot size 2001-10000)80 tiles

Permissible defective tiles (Visual, Sample size 80)7 tiles

Sample size for physical tests (per 20000 tiles)5 tiles

Criteria for conformity for breaking loadThe average breaking load should not be less than the specified minimum.

Practical Notes

Ensure that the samples are drawn randomly from the entire lot, not just from the top or sides of a stack, to get a representative sample.

The standard distinguishes between sampling for visual checks (like warpage, cracks) and destructive physical tests (like water absorption, breaking load).

Samples for physical tests are to be selected from the tiles that have already passed the visual inspection.