Corrugated coir wood wool cement roofing sheets-Specification
1982 Edition

IS 10388 mandates the use of indigenous natural fibers such as coir and woodwool for manufacturing corrugated roofing sheets combined with cement. Coir fibers, obtained from coconut husks, are valued for their strength and moisture resistance, while woodwool fibers consist of fine wood shavings that contribute to thermal insulation and fire resistance. Both fibers must be clean and free from contaminants, mixed in appropriate ratios with cement to produce roofing sheets that offer improved insulation and reduced reliance on asbestos. This promotes an environmentally friendly and economical roofing solution using local materials.

According to Clause 3.1 and the dimensional Table 1 of IS 10388, the following tolerances apply: Length and width dimensions allow a margin of plus or minus 10 mm; thickness has a tolerance of + free / - 0.5 mm; the depth of corrugation may vary by +3 mm / -6 mm; and the pitch of corrugation is permitted a variation of +6 mm / -2 mm measured across six pitches. Thickness is determined as the average of six measurements along the sheet width excluding valleys, while depth and pitch are measured with precision tools to ensure uniformity. These tolerances ensure sheets maintain consistent geometry and are free from defects impacting functionality and appearance.

The transverse strength test involves conditioning the roofing sheets by immersing them in water at 27 ± 2°C for 24 hours. The sheet is then supported on two hardwood bearers, each 75 mm wide by 150 mm deep, spaced 1 meter apart and oriented perpendicular to the corrugations. Load is applied uniformly along the sheet’s centerline via a 225 mm by 75 mm runner at a rate not exceeding 20 N/min. The breaking load is recorded, and the average (X) and range (R) of test results are calculated. The acceptance criterion is that X minus half the range (X - 0.5R) should be equal to or greater than the minimum limit specified in Table 2 of Appendix A. Only lots meeting this threshold pass the transverse strength requirement.

The roofing sheets must not exceed a maximum water absorption of 30% by weight. Specimens used for this test should be at least four weeks old. Water absorption is calculated by weighing the specimen after immersion (W1) and after drying/heating (W2), using the formula: ((W1 - W2) / W2) × 100%. The procedure involves drying the specimen to a constant weight, immersing it in water for a specified period, removing and surface drying it, then weighing it again. Additionally, impermeability tests ensure no water droplets form on the underside of the sheet, although traces of moisture are allowed. These tests verify the sheet’s durability and resistance to moisture ingress.

IS 10388 primarily covers material composition, dimensional accuracy, and physical properties like water absorption, impermeability, and acid resistance. It does not explicitly specify fire resistance or thermal insulation performance criteria within its clauses or appendices. While the woodwool-cement sheets inherently provide some thermal insulation due to the porous nature of wood fibers and exhibit non-combustible characteristics from the cement matrix, detailed fire resistance and insulation properties are governed by other standards such as IS 1642 or international standards like ISO 834 and ASTM E119. For comprehensive assessment of fire and thermal behavior, those standards should be consulted.