corrugated bitumen roofing sheets
1988 Edition

Under the standard for corrugated bitumen roofing sheets, the bitumen content should not exceed 50% ± 5% by weight. Additionally, the bitumen distribution between the outer and central layers must not differ by more than 5%. The bitumen used must comply with the IS 73:1992 specification for paving bitumen, ensuring adequate durability and resistance against weathering. Other relevant parameters include ash content limited to 10%, water absorption capped at 8%, and impermeability requirements that prevent moisture presence on the underside of the sheets. These conditions ensure the sheets provide effective waterproofing, structural integrity, and longevity.

The standard specifies corrugated bitumen roofing sheets in sizes of 1200 mm length by 750 mm width, with thickness ranging from 3 to 5 mm. The sheets feature a corrugation depth of 35 mm and a pitch of 90 mm. Dimensional tolerances allowed include ±15 mm on length and ±20 mm on width. Thickness is measured as the average of six readings across the width using a screw gauge with a 9 mm anvil diameter, with an additional tolerance of +1 mm permitted. These dimensional controls ensure proper fitting and optimal performance in roofing installations.

The standard mandates that corrugated bitumen roofing sheets must withstand a minimum breaking load of 100 kg (1000 N). The breaking load is evaluated by gradually applying tensile force to the specimen until failure, using a universal testing setup. For impact resistance, sheets are supported on two rigid wooden beams spaced 600 mm apart, perpendicular to the corrugation, with a third wooden piece applying load centrally. The sheets must show no signs of tearing, cracking, or breaking under this impact. These tests confirm the mechanical robustness and safety of the roofing sheets.

Sampling for conformity follows simple random procedures in accordance with IS 4905:1968. Each lot is sampled individually, with sample sizes and permissible numbers of defective sheets determined based on lot size, as outlined in the standard's acceptance tables. For example, small lots of up to 25 sheets require 8 samples with zero allowed defects, while larger lots have proportionally larger sample sizes and permitted defect counts. Visual and dimensional inspections are performed first; if defects are within acceptable limits, further tests on sub-samples are conducted. Lots exceeding defect thresholds are rejected, ensuring consistent product quality.

To ensure long-term performance, the standard prescribes accelerated weathering tests where specimens undergo 2000 hours in a weatherometer cycling through water spray combined with sunlight and light-only phases. Post-exposure assessments evaluate surface cracks, color changes, flexibility, sagging, and other defects, averaging results from five samples. Temperature susceptibility testing involves monitoring moisture formation and cracking on the sheet undersides, with averages from two specimens recorded. These evaluations simulate environmental stresses, verifying that the sheets maintain integrity and function over time under fluctuating weather and temperature conditions.