Roofing Slate Tiles
1981 Edition

According to IS 6250 (1981), roofing slate tiles must conform to specific dimensional tolerances: Length and breadth are allowed a variation of plus or minus 5 millimeters, with standard sizes of 600 mm or 500 mm in length and 300 mm or 250 mm in breadth. Thickness must be a minimum of 15 mm with an allowable tolerance of ±2 mm. Tiles should be free from structural defects such as cracks and veins, and exhibit uniform texture and straight cleavage to ensure proper fit and longevity in roofing applications.

The water absorption test involves drying slate tile specimens at 105 to 110°C until reaching a constant weight (denoted as A), then immersing them in clean water at 27 ± 2°C for 24 hours. After immersion, specimens are weighed again within three minutes (weight B). The percentage water absorption is calculated as ((B - A)/A) × 100. Six specimens are tested and the average absorption is reported. The acceptable maximum average water absorption is 2% by mass, with individual sample variation not exceeding 20% of this average. Compliance ensures tiles' resistance to moisture ingress as per IS 6250.

Slate tiles are subjected to several physical durability tests under IS 6250, including: water absorption (maximum average 2% mass with ≤20% variation), modulus of rupture for mechanical strength (minimum 60 N/mm² dry, 40 N/mm² wet), depth of surface softening (not exceeding 0.05 mm), permeability test to ensure no water seepage through the tile, sulphuric acid immersion test to evaluate chemical resistance (if requested), and wetting and drying cycles to verify resistance to delamination and surface damage. Specimens for these tests are prepared as 50x50 mm samples with smooth edges, ensuring comprehensive evaluation of durability.

Sampling is conducted randomly from the lot according to its size, with sample quantities and permissible defective counts specified in IS 6250 Table 2. For example, lots up to 10,000 tiles require 30 samples with a maximum of 3 defective allowed. Each sampled tile is inspected for shape, uniform thickness, intact corners, edge accuracy, surface finish matching the approved standard, and absence of veins, cracks, or deleterious minerals. Specimens for physical testing are then prepared by carefully cutting three 50x50 mm pieces from each tile, with edges ground smooth under water to prevent damage. Tiles failing any criteria are deemed defective, ensuring only acceptable products pass.

Each roofing slate tile must bear a clear manufacturer's identification mark or initial, as per the standard's mandatory marking requirements. Additionally, tiles may display the ISI Certification Mark, which signifies compliance verified through ISI's inspection and quality assurance processes. The use of the ISI mark is subject to licensing and governed by the Indian Standards Institution (Certification Marks) Act. These markings ensure traceability, quality assurance, and consumer confidence in the product's adherence to IS 6250 specifications.