Hydrated Lime Specifications & Quality Standards: IS 712 Explained
A complete breakdown of hydrated lime quality standards — IS 712 classes, purity grades, fineness requirements, testing methods, and how to read a test certificate. Essential reading for procurement managers and quality engineers.
Hydrated Lime Specifications & Quality Standards: IS 712 Explained
Frequently Asked Questions
What are the IS 712 requirements for hydrated lime?
IS 712 specifies two classes of hydrated lime. Class C requires minimum 65% Ca(OH)₂, maximum 4% MgO, maximum 5% CO₂, maximum 2% moisture, and maximum 10% residue on 90-micron sieve. Class S requires minimum 90% Ca(OH)₂, maximum 4% MgO, maximum 3% CO₂, maximum 2% moisture, and maximum 5% residue on 90-micron sieve. Both classes require 0% residue on 600-micron sieve and must pass the Le Chatelier soundness test.
What is the difference between IS 712 Class C and Class S hydrated lime?
Class C requires minimum 65% Ca(OH)₂ and is used for construction and general industrial applications. Class S requires minimum 90% Ca(OH)₂ and is used for water treatment and food-grade applications. Class S also has a stricter CO₂ limit (3% vs 5%) and fineness requirement (5% vs 10% residue on 90-micron sieve). For most industrial applications, Class S or equivalent purity is recommended even when Class C is the minimum requirement.
How do I verify that a hydrated lime test certificate is genuine?
A genuine test certificate should include: the batch number and test date (within 60 days of supply), all IS 712 parameters (Ca(OH)₂, MgO, CO₂, moisture, fineness on three sieves, soundness), reference to IS 1514 test methods, and laboratory details. For critical applications, request testing by a NABL-accredited third-party laboratory. You can also take a sample from the delivered batch and have it independently tested.
Why does high MgO content in hydrated lime cause problems?
High MgO in hydrated lime comes from magnesium carbonate (MgCO₃) in the original limestone. MgO causes unsoundness — delayed expansion after the lime has been used in a product. This is particularly damaging in AAC blocks (causes cracking after manufacture), mortar and plaster (causes popping and spalling), and concrete (causes expansion and cracking). IS 712 limits MgO to 4% for both classes. For AAC block manufacturing, many producers specify MgO below 2%.
What fineness is required for hydrated lime in road construction?
For road construction (BC and DBM bituminous mixes), MoRTH specifications require hydrated lime with 90% passing 350 mesh (43 micron). This is finer than IS 712 requires (which specifies maximum 10% residue on 90-micron sieve = 90% passing 90 micron). Not all suppliers can meet the 350-mesh (43-micron) fineness requirement — always confirm this specification before ordering road-grade lime.
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