Silica-asbestos-cement Flat Sheets
1990 Edition

According to the standard, permitted cements for manufacturing silica-asbestos-cement flat sheets include 33 Grade Ordinary Portland Cement complying with IS 269:1989, Portland Pozzolana Cement adhering to IS 1489:1976, and Blast Furnace Slag Cement following IS 455:1989. These cements chemically react with silica and are reinforced with asbestos fibers, with the option to incorporate compatible pozzolanic materials, fillers, and pigments to enhance properties.

The classification system divides these sheets into Class I and Class II based on minimum bending stress and density requirements. Class I sheets must have a bending stress of at least 13 N/mm² parallel to fibers and 16 N/mm² perpendicular to fibers, with a minimum density of 2.0 g/cm³. Class II sheets require higher bending stresses of 20 N/mm² parallel and 28 N/mm² perpendicular to fibers, and a minimum density of 2.16 g/cm³. If fiber orientation is uncertain, the lower stress value should exceed the parallel threshold and the higher value should meet or exceed the perpendicular threshold.

The standard specifies that edge straightness should not deviate more than 2 mm per meter length or width. While explicit tolerances for length and width are not detailed in the provided text, typical values range between ±2 mm to ±5 mm depending on sheet size. Thickness tolerance generally follows ±0.5 mm for sheets between 3 mm and 5 mm thick, and a positive tolerance of 0.1 times the nominal thickness for sheets 6 mm and thicker. The maximum thickness variation within a single sheet should not exceed 10% of the maximum measured thickness.

Testing to verify bending stress and density is conducted according to IS 5913:1989. Bending stress is measured in two directions—parallel and perpendicular to asbestos fibers—with minimum values outlined by sheet class. Density testing ensures sheets meet or exceed the specified minimum density of 2.0 g/cm³ for Class I and 2.16 g/cm³ for Class II. These measurements confirm the mechanical integrity and classification compliance of the sheets.

Each sheet must be clearly and permanently marked with the sheet class, manufacturer’s identification, date and year of production, and nominal thickness in bold lettering. Additionally, a pictorial warning sign as specified in IS 12081 (Part 2):1987 must be displayed. Deliveries are required to include a Safety Rules Sheet per IS 11769 (Part 1):1987, which provides essential instructions on safe handling, storage, and installation to mitigate health risks associated with asbestos-containing materials.