Link points to Internet Archive / others. Not hosted by InfraLens. Details
IS 6250:1981 is the Indian Standard (BIS) for roofing slate tiles. This standard specifies the requirements for natural slate tiles intended for roofing. It covers material characteristics, dimensions, tolerances, physical properties like water absorption and strength, and the test methods to verify conformity.
! This standard is crucial for heritage and conservation projects where slate roofing is common.
! Slate is a natural, brittle material; proper handling, storage, and installation techniques are critical to avoid breakage.
! The 'ring test' (tapping the slate to hear a clear sound) is a common on-site qualitative check for hidden cracks, though not a formal test in this standard.
Slate and stone for roofing and cladding - Part 1: Specifications for slate and carbonate slate
Both specify requirements and test methods for natural slate roofing tiles.
ASTM C406 / C406M - 15(2021)ASTM International, USA
HighCurrent
Standard Specification for Roofing Slate
Both define grades, physical properties, and dimensions for roofing slate.
BS 680-2:1971BSI (British Standards Institution), UK
MediumWithdrawn
Specification for roofing slates - Part 2: Metric units
Covers similar material properties, but uses older testing methods and classifications.
Key Differences
≠IS 6250 provides a single set of criteria, whereas ASTM C406 classifies slate into three grades (S1, S2, S3) based on expected service life, and BS EN 12326 uses a detailed coding system for performance characteristics (e.g., T1/T2/T3 for thermal cycling).
≠IS 6250 sets a simple maximum limit for calcium carbonate content (20%). BS EN 12326 has a more complex approach, classifying slates with >20% carbonate as 'carbonate slate' and subjecting them to specific sulphur dioxide exposure tests (S1, S2, S3 classes) to determine durability.
≠BS EN 12326 and other standards for cold climates mandate a frost resistance or thermal cycling test. IS 6250:1981 does not include any requirement for frost or thermal cycle testing.
≠The minimum required Modulus of Rupture in IS 6250 (45 MPa) is significantly lower than that required by ASTM C406 (approx. 62 MPa / 9000 psi).
Key Similarities
≈All standards are fundamentally for natural stone slate quarried for roofing purposes, explicitly excluding artificial or manufactured slate products.
≈Water absorption is used as a primary indicator of slate quality and durability across all standards, with lower absorption values consistently indicating higher quality material.
≈All standards include requirements for minimum bending strength (Modulus of Rupture) to ensure the slates can withstand service loads like snow, wind, and foot traffic during installation.
≈All standards specify requirements for workmanship, including straight edges, flatness, freedom from cracks, and the proper formation of nail holes.
Parameter Comparison
Parameter
IS Value
International
Source
Water Absorption (Maximum)
≤ 0.60%
≤ 0.25% (for top grade, S1)
ASTM C406
Modulus of Rupture (Minimum)
45 MPa
≥ 62 MPa (9000 psi)
ASTM C406
Calcium Carbonate Content
≤ 20%
Classified as 'carbonate slate' if >20% and subject to specific SO₂ test (S1, S2, S3).
BS EN 12326-1
Weather Resistance Test Criteria
≤ 0.2% weight loss in acid immersion
≤ 0.05 mm (0.002 in) depth of softening in acid for Grade S1
ASTM C406
Thermal Cycling / Frost Resistance Test
Not specified
Required (Classified as T1, T2, or T3)
BS EN 12326-1
Nominal Thickness
4 mm to 6 mm
4.8 mm to 7.9 mm (3/16 to 5/16 in) is typical, but varies widely
ASTM C406
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Maximum average water absorption0.6 percent
Minimum average modulus of rupture (wet)60 MPa
Maximum allowable increase in weight (Weathering Test)0.2 mg/cm²
Nominal thickness range4 to 6 mm
Thickness tolerance±1 mm
Tables & Referenced Sections
Key Tables
Table 1 - Dimensions of Roofing Slates
Table 2 - Physical Requirements of Roofing Slates
Key Clauses
Clause 3 - Dimensions and Tolerances
Clause 4 - Physical Requirements
Clause 5 - Tests
Clause 6 - Sampling and Criteria for Conformity
Frequently Asked Questions4
What is the maximum allowed water absorption for roofing slate?+
The maximum average water absorption should not exceed 0.6 percent by mass (Clause 4.2 & Table 2).
What are the standard thicknesses for slate tiles under this code?+
The nominal thickness ranges from 4 mm to 6 mm, with a tolerance of ±1 mm (Table 1).
What is the minimum required strength for roofing slate?+
The minimum average modulus of rupture, when tested in a wet condition, must be 60 MPa (Clause 4.4 & Table 2).
How is the durability or weather resistance of slate checked?+
Through a sulphuric acid test where the increase in weight should not exceed 0.2 mg/cm² (Clause 4.3 & Table 2).