Specification for Building Limes
1984 Edition

IS 712 categorizes building limes into six distinct classes based on their characteristics and intended use: Class A (eminently hydraulic lime used structurally, supplied hydrated), Class B (semi-hydraulic lime for masonry mortars and plaster undercoats), Class C (fat lime suitable for finishing coats and whitewashing), Class D (magnesium or dolomitic lime for finishing and plastering), Class E (kankar lime primarily for masonry mortars, supplied hydrated), and Class F (siliceous dolomitic lime for plaster base and finishing layers). Classes A and E are exclusively available in hydrated form, while others can be supplied as quicklime or hydrated lime. These classifications guide selection based on structural or finishing needs.

Building limes under IS 712 must comply with defined chemical criteria detailed in Table 1 (Clause 4.1). Core chemical requirements include a minimum calcium oxide (CaO) and magnesium oxide (MgO) content depending on the lime class, restricted magnesium oxide levels especially in dolomitic limes, limits on insoluble residues to control impurities, and maximum allowable loss on ignition to maintain purity. For example, hydraulic and semi-hydraulic limes have higher CaO content requirements, while magnesium lime allows higher MgO. These standards ensure the lime’s suitability for structural integrity and durability. Exact percentages and detailed values are specified within the standard's chemical tables.

Sampling of quicklime and hydrated lime according to IS 712 involves systematic collection to ensure representativeness. For bulk quicklime, at least 50 equal portions are taken at intervals during handling or from various stockpile sections, then mixed and reduced by coning and quartering to a gross sample of 20 kg for lump and 10 kg for powdered forms. Packaged quicklime requires opening at least 25% of packages with portions taken from each and similarly prepared. Hydrated lime samples are collected similarly to powdered quicklime with final samples weighing no less than 5 kg. From each lot, three final test samples are prepared for analysis to maintain consistency and reliability.

IS 712 specifies several physical tests to confirm lime quality: free moisture content must not exceed 2%, and available lime as calcium oxide should be at least 75% on a dry basis. Mechanical strength tests include transverse strength at 28 days, with minimum values prescribed. Additionally, workability is assessed through bump tests, volume yield measurements gauge lime reactivity, and stability is checked via soundness and expansion tests (Chaterlier expansion). Popping and pitting inspections are performed on hydrated lime to detect defects. Proper storage in dry conditions is emphasized to preserve properties. These assessments collectively ensure the lime’s performance and durability in construction.

According to IS 712, hydrated lime must be packed in appropriate containers such as jute bags with polyethylene lining, high-density polyethylene woven bags lined with polyethylene, or craft paper bags, typically weighing 50 kg. If the lime is planned for use within 30 days, the lining may be omitted. Each package must be clearly marked with the lime type and class, manufacturer’s brand name, date of production, net weight, and for quicklime, the slaking temperature. These measures ensure traceability, facilitate quality control, and promote safe handling in line with the standard’s requirements.