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IS 3102:1971 is the Indian Standard (BIS) for classification of burnt clay solid bricks. This standard classifies burnt clay solid bricks based on their average compressive strength. It provides a numerical classification system (ranging from Class 35 to Class 350) to replace older descriptive grading systems, ensuring standardized brick specification for structural and non-structural masonry work.
Lays down the classification of burnt clay solid bricks based on their compressive strength.
! Avoid using outdated descriptive terms like 'First Class' or 'Second Class' bricks in BOQs and specifications; always use the specific strength-based classes (e.g., Class 75) defined in this code.
! The class number directly corresponds to the minimum average compressive strength of the brick in kg/cm2.
! Actual testing to verify the classification must be conducted in accordance with IS 3495.
Consolidated list per BIS. For the text of each amendment, refer to the BIS portal link above.
burnt clay brickssolid bricksmasonry
International Equivalents
Similar International Standards
ASTM C62-23ASTM International, USA
HighCurrent
Standard Specification for Building Brick (Solid Masonry Units Made From Clay or Shale)
Specifies requirements for solid clay bricks, including grading based on strength and durability.
BS EN 771-1:2011+A1:2015BSI - British Standards Institution, UK (European Standard)
HighCurrent
Specification for masonry units - Part 1: Clay masonry units
Comprehensive specification for all types of clay masonry units, including solid bricks.
AS/NZS 4455.1:2008Standards Australia / Standards New Zealand
MediumCurrent
Masonry units, pavers, flags and segmental retaining wall units - Part 1: Masonry units
Covers requirements for various masonry units, including clay bricks, with classification by strength.
Key Differences
≠IS 3102 classifies bricks solely based on average compressive strength. International standards like ASTM C62 use a multi-factor grading system including weathering resistance (based on water absorption and saturation coefficient) in addition to strength.
≠IS 3102 is a pure classification standard from 1971. International equivalents like BS EN 771-1 are comprehensive product specifications requiring manufacturers to declare a range of performance characteristics (strength, dimensions, durability, thermal properties).
≠Durability requirements, such as freeze-thaw resistance, are mandatory in ASTM C62 for exterior applications in relevant climates, but are not addressed in IS 3102.
≠IS 3102 uses legacy units (kgf/cm²) for strength classification, whereas all modern international standards use Megapascals (MPa) or Newtons per square millimeter (N/mm²).
Key Similarities
≈Compressive strength is the primary and fundamental characteristic used for classification and specification across all standards.
≈All standards serve the same core purpose: to provide a reliable system for specifying and procuring clay bricks to ensure minimum structural performance.
≈The concept of a 'solid' brick is commonly defined in all standards, typically based on a maximum allowable percentage of voids or perforations (usually <25%).
≈All standards recognize the importance of dimensional regularity for quality masonry and specify limits on dimensional deviations, either as absolute tolerances or performance categories.
Parameter Comparison
Parameter
IS Value
International
Source
Compressive Strength Classification
Classes based on average strength in kgf/cm², e.g., 'Class 100' = 100 kgf/cm² (~9.8 N/mm²)
Minimum average compressive strength for Grade SW (severe weathering) is 20.7 MPa (~211 kgf/cm²)
ASTM C62-23
Water Absorption (by 24-hr cold soak)
Not in IS 3102. Related standard IS 1077 specifies max 20% by weight for bricks up to class 12.5.
Maximum average 17.0% by weight for Grade SW.
ASTM C62-23
Definition of 'Solid' Unit
Solid brick with no perforations (frogs up to 20% volume allowed per IS 1077).
Net cross-sectional area is ≥75% of gross area in every plane parallel to the bearing surface.
ASTM C62-23
Freeze-Thaw Resistance
No requirement or test method specified.
Mandatory for Grade SW; must pass 50 cycles of freezing and thawing without damage.
ASTM C62-23
Dimensional Tolerance Declaration
Fixed tolerances specified in related standard IS 1077 (e.g., ±8mm for length over a sample of 20).
Manufacturer declares a tolerance category (e.g., T1, T2, Tm) and a range category (R1, R2).
BS EN 771-1:2011+A1:2015
Standard 'Work' Size
Specifies standard sizes, e.g., 190x90x90 mm (modular) and 230x110x70 mm (non-modular).
Manufacturer declares the 'work size'; no single standard size is mandated (e.g., a common UK size is 215x102.5x65 mm).
BS EN 771-1:2011+A1:2015
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Class 35 minimum average compressive strength35 kg/cm2 (~3.5 N/mm2)
Class 50 minimum average compressive strength50 kg/cm2 (~5.0 N/mm2)
Class 75 minimum average compressive strength75 kg/cm2 (~7.5 N/mm2)
Class 100 minimum average compressive strength100 kg/cm2 (~10.0 N/mm2)
Class 350 minimum average compressive strength350 kg/cm2 (~35.0 N/mm2)