Ceramic unglazed vitreous acid-resisting tile
2007 Edition

According to IS 4457, vitrified tiles should not exceed 0.5% water absorption, reflecting their impervious nature and resistance to acid and stains. Other ceramic tiles have a maximum allowable water absorption of 1.5%. Curved tiles are exempt from these water absorption limits. Water absorption is calculated by comparing the wet and dry masses of the tile, using the formula: ((wet mass - dry mass) / dry mass) × 100. This ensures that tiles meet durability and chemical resistance standards.

The chemical resistance test involves partial immersion of tile samples in selected chemical solutions for a duration of 28 days. Post exposure, visual inspections are conducted on the tile’s main surface as well as cut and non-cut edges to detect discoloration or surface deterioration. Test solutions include acids and alkalis of varying concentrations, household chemicals, pool salts, and concentrated nitric and sulfuric acids. The resistance classification is mutually agreed upon by the producer and purchaser based on observed damage. Test reports document tile descriptions, test chemicals used, number of samples tested, and any visual changes observed.

IS 4457 specifies that acid-resisting tiles typically have a thickness of 7.5 mm or more, up to a maximum of 20 mm. Tiles thinner than 7.5 mm are also covered but have adjusted mechanical requirements. While precise dimensional tolerances are not exhaustively detailed, the standard aligns with ISO norms and encourages agreements between manufacturers and buyers to ensure modular compatibility. Additionally, abrasion resistance and flexural strength tests are mandatory, with a modulus of rupture averaging around 35 N/mm² for tiles with breaking strength under 3000 N.

The standard recommends a deep abrasion resistance test using a rotating steel disc apparatus made from Fe 410-S steel, 200 mm in diameter, rotating at 75 rpm. The tile specimen is pressed tangentially against the disc while white fused aluminum oxide abrasive (Grit No. 80) is fed uniformly. The pressure is calibrated so that after 300 revolutions, a groove chord length of 32 mm is formed on a reference granite sample. The abrasion resistance is then assessed by measuring the groove length created on the tile surface, ensuring repeatable and standardized evaluation.

Conformity assessment per IS 4457 involves selecting sample sizes based on batch quantity, with acceptance numbers specifying the maximum allowable defective tiles. For example, lots up to 8 tiles require 5 samples with zero defects allowed, while lots exceeding 500 tiles require 50 samples with up to 3 defects accepted. Random sampling follows IS 4905 guidelines. Each sampled tile undergoes checks for dimensional accuracy, marking, edge straightness, and surface flatness. Additional tests are conducted for larger lots (101-300 tiles: one extra test; above 300 tiles: two extra tests). Lots pass conformity only if all tests meet criteria, ensuring statistically robust quality control.