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IS 1635:1992 is the Indian Standard (BIS) for field slaking of building lime and preparation of putty. This code covers the recommended procedures for the field slaking of building quicklime and the preparation of lime putty. It specifies the equipment, methods, and maturing times required to ensure complete hydration and prevent defects like pitting or popping in finished plaster or mortar.
Code of practice for field slaking of building lime and preparation of putty
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Building Limes and Gypsum Products
! Always add lime to water gradually, rather than water to lime, to prevent violent exothermic reactions and dangerous splattering.
! Ensure the putty is properly matured; using un-matured putty can lead to 'popping' or 'pitting' in plaster due to delayed hydration of unslaked particles.
! During maturation, lime putty should be protected from drying out by maintaining a thin layer of water over its surface.
Standard Specification for Lime Putty for Structural Purposes
Specifies requirements for the final product (lime putty), which is the intended output of the process described in IS 1635.
BS EN 459-1:2015BSI, United Kingdom / CEN, Europe
MediumCurrent
Building lime - Part 1: Definitions, specifications and conformity criteria
Defines and classifies the raw material (building lime) used in the slaking process, but does not detail the on-site slaking practice itself.
ASTM C5-18(2023)ASTM International, USA
MediumCurrent
Standard Specification for Quicklime for Structural Purposes
Provides the specification for quicklime, the primary input material for the slaking process covered by IS 1635.
Key Differences
≠IS 1635 is a prescriptive 'Code of Practice' detailing the on-site method of slaking and putty preparation. Modern international standards like ASTM C1489 are performance-based, specifying the properties of the final putty rather than the manufacturing process.
≠IS 1635 explicitly specifies minimum maturing times for lime putty (e.g., 2-3 weeks for fatlime). International standards do not specify a maturing time, instead requiring the final product to meet performance tests (like plasticity), which implicitly necessitates sufficient maturing.
≠The Indian standard provides detailed procedural guidance suitable for manual, on-site operations (e.g., platform vs. tank slaking dimensions). This type of 'how-to' guidance is generally absent from ASTM or EN standards, which leave the method to the manufacturer or to separate industry practice guides.
≠IS 1635 is focused on field/site-based production, whereas standards like ASTM C1489 cover both field- and factory-produced lime putty without distinction, as long as the final product meets the specification.
Key Similarities
≈Both IS 1635 and related international standards share the same fundamental goal: to produce a well-slaked, consistent lime putty free of unslaked particles, suitable for use in building mortars and plasters.
≈All standards recognize the crucial difference between various types of lime. IS 1635 distinguishes between fatlime (Class C) and hydraulic lime (Class B), while EN 459-1 has a detailed classification system (CL, NHL, etc.), both acknowledging that different limes require different slaking procedures and have distinct properties.
≈The principle of removing unslaked particles and impurities is common. IS 1635 mandates 'running' the slaked lime through a sieve, while ASTM C1489 achieves the same outcome by setting a maximum limit on the residue retained on a specific sieve.
≈The underlying safety principles are identical. IS 1635 lists specific precautions (goggles, gloves) for handling caustic quicklime. This aligns with universal health and safety requirements mandated by regulations and material safety data sheets that accompany products under international standards.
Parameter Comparison
Parameter
IS Value
International
Source
Putty Maturing Time (Fat Lime)
Prescribed as 'not be less than 2 to 3 weeks'.
Not specified; performance-based. The putty must meet final property requirements, implying sufficient maturation.
ASTM C1489-18(2023)
Screening of Putty
Process requirement: Run through a 2.36 mm IS Sieve.
Final product requirement: Max. residue of 15% on an 850-µm (No. 20) sieve and 2% on a 300-µm (No. 50) sieve.
ASTM C1489-18(2023)
Plasticity Requirement
No quantitative value; described as achieving a 'creamy consistency'.
Quantitative requirement: Plasticity figure of not less than 200 when tested per ASTM C110.
ASTM C1489-18(2023)
Putty Density
Not specified.
Minimum density of 1360 kg/m³ (85 lb/ft³).
ASTM C1489-18(2023)
Source Quicklime Specification
Refers to IS 712, which covers Class B (semi-hydraulic) and Class C (fatlime).
Must conform to ASTM C5 (Specification for Quicklime for Structural Purposes).
ASTM C1489-18(2023)
Soaking Time for Hydrated Lime Putty
Soak in water for at least 24 hours.
Not specified; only the final putty properties are regulated.
ASTM C1489-18(2023)
⚠ Verify details from original standards before use
Key Values3
Quick Reference Values
Minimum maturing time for Class C (fat lime) putty2 to 3 days
Minimum maturing time for Class B (semi-hydraulic) putty12 hours
Sieve size for screening milk of lime (coarse impurities)3.35 mm IS Sieve
How long should fat lime (Class C) putty be matured before use?+
It should be allowed to mature for a minimum of 2 to 3 days to ensure all particles are fully hydrated.
What is the key difference when slaking semi-hydraulic lime (Class B) vs fat lime?+
Semi-hydraulic lime requires less maturing time (around 12 hours) and should be used relatively quickly, as it can slowly set under water.
What safety precautions are required during slaking?+
Workers must use protective gear such as goggles, rubber gloves, and boots due to the highly caustic nature and intense heat generated during the slaking of quicklime.