IS 712 : 1984Building Limes - Specification

IS 712 is the specification for building limes — quicklime (CaO), hydrated lime (Ca(OH)₂), and various lime classes used in mortar, plaster, soil stabilisation, and as a cement supplement. Despite the dominance of cement, lime remains relevant in:

• Heritage / conservation of historic buildings (lime mortar matches original)
• Soil stabilisation of expansive (black cotton) soils (IRC SP 70:2005)
• Lime-cement mortar for masonry — flexible, breathable
• Lime plaster + finishing coat — traditional, breathable, white aesthetic
• Whitewash / colour wash for traditional finishes
• Lime-stabilised brick (alternative to fired brick)
• Sewage / water treatment (precipitation, pH adjustment)
• Industrial use (steel-making flux, pulp + paper, leather, sugar)

IS 712 categorises building limes by chemical composition + physical properties.

The contemporary cement/concrete construction often eliminates lime, but lime is making a comeback in green building (lower embodied carbon than cement) and restoration work. For masonry mortar in heritage / conservation, traditional 1:1:6 (cement:lime:sand) mortar adds workability + breathability vs straight cement-sand.

Class A (Eminently Hydraulic Lime): - High calcium silicate content (sets under water) - Used in waterproof mortar, marine masonry, water-storage structures - Compressive strength 7 days: ≥ 1.75 MPa; 28 days: ≥ 2.8 MPa

Class B (Semi-Hydraulic Lime): - Moderate hydraulic property - Used in masonry mortar, undercoats of lime plaster - Compressive strength 7 days: ≥ 1.25 MPa; 28 days: ≥ 1.75 MPa

Class C (Fat Lime / High-Calcium Lime): - Pure calcium oxide (very low silicate); sets only by carbonation in air - Used in finishing coats of lime plaster, whitewash, distemper - Slow setting; not for water-contact

Class D (Magnesian / Dolomitic Lime): - High magnesium content (MgO) - Used in finishing coats; better workability than Class C - Slow setting

Class E (Kankar Lime): - Made from kankar (calcareous nodule from black cotton soil zones) - Locally available in Maharashtra, Gujarat, MP, Rajasthan - Used in rural lime works, plaster

Class F (Siliceous Dolomitic Lime): - Specific to certain mining areas - Used in localised regions

Forms: - Quicklime (lump) — CaO; reactive with water (caution: heat release) - Hydrated lime (powder) — Ca(OH)₂; pre-slaked, ready to use - Putty (slaked overnight) — high-quality plaster lime - Lime mortar (pre-mixed) — supplied ready to use

Acceptance properties (IS 712 Tables 1-6):

| Property | Class A | Class B | Class C | |---|---|---|---| | Free lime CaO + MgO (min %) | 70 | 60 | 70 | | Insoluble residue (max %) | 25 | 35 | 5 | | Loss on ignition (max %) | 25 | 25 | 27 | | Compressive strength 28d (MPa) | 2.8 | 1.75 | — (sets only by carbonation) | | Setting time (initial, min) | 30 | 60 | — | | Fineness (residue on 850 µm sieve, max %) | 15 | 25 | 5 |

Bulk density: - Quicklime (lump): 1700-2200 kg/m³ (affects storage volume) - Hydrated lime (powder): 600-700 kg/m³ (lower — voids in powder) - Lime putty: 1300-1500 kg/m³

Slaking: - Mass increase from quicklime to hydrated: ~30 % (water added) - Volume change: 2-3× expansion - Heat release: ~1100 kJ/kg of CaO; can boil water; safety concern

Storage: - Quicklime: airtight (absorbs moisture from air, slakes prematurely); 6-month maximum useful life - Hydrated lime (bagged): 6-12 month useful life if stored dry; 30-50 % strength loss after 12 months - Putty: indefinite if kept wet under water layer

Lime mortar mixes (typical):

| Application | Mix (lime : sand) | Compressive strength (typical) | |---|---|---| | Heavy load-bearing | 1 : 3 (Class A or B) | 2-4 MPa | | Standard masonry | 1 : 4 to 1 : 6 (Class B) | 1-2 MPa | | Plaster undercoat | 1 : 2 (Class C) | 0.5-1 MPa | | Plaster finishing | 1 : 1 (Class C) | — | | Whitewash | thinned with water | n/a |

Lime-cement-sand (compound) mortar: - 1:1:6 (cement:lime:sand) — heritage / breathable / flexible - 1:2:9 — very lean masonry mortar - 1:3:12 — pointing in dry zones

Lime stabilisation of soil (IRC SP 70:2005): - 4-6 % lime by mass for soils with PI 20-40 (modification + stabilisation) - 3-4 % lime for PI 15-20 (modification only — workability improvement) - > 6 % lime for very plastic clays (PI > 40) - Initial drying effect (faster pavement work) + long-term strength gain (pozzolanic reaction)

• IS 1905:1987 — code of practice for structural use of unreinforced masonry (mortar provisions).
• IS 1077:1992 — burnt clay bricks (mortar with bricks).
• IS 6041 — code of practice for construction of AAC block masonry.
• IS 6042 — light-weight concrete block masonry construction.
• IS 8112 / IS 12269 / IS 1489 / IS 269 — cement standards (for cement-lime compound mortars).
• IS 383:2016 — sand specification for mortar.
• IS 4031 (Parts 1-15) — physical tests on cement (lime + cement compound mortar testing borrows methods).
• IS 6932 (multiple parts) — methods of testing of building limes.
• IRC SP 70:2005 — cement-treated and recycled materials in road construction (lime stabilisation).
• IRC:91:2018 — guidelines for construction of pavements on expansive soils (lime stabilisation).
• NBC 2016 Part 5 — building materials.
• IS 14143 — drinking water standards (lime used in water treatment for pH adjustment).
• IS 4926 / IS 4925 — for concrete using portland cement (lime + cement combinations rare in concrete).
• IS 712 (this code) — building limes specification.

1. Quicklime stored in damp environment. Slakes prematurely, heat release can ignite combustible storage; loss of useful CaO. Store in dry, vented room. 2. Hydrated lime stored too long (> 12 months). Carbonates with atmospheric CO₂; loses reactivity; mortar weak. Use FIFO; reject lime > 6 months stored. 3. Skipping slaking step for quicklime. Adding quicklime directly to mortar mix → boils, separates, pop-outs. Always slake to putty or hydrated form before mixing. 4. No fineness check. Coarse lime particles don't react fully; mortar weak. Verify residue on 850 µm sieve ≤ class limit. 5. Class C (fat lime) used in load-bearing mortar. Sets only by carbonation; very slow strength gain; weak. Use Class A or B for load-bearing. 6. Lime mortar curing skipped. Lime mortar carbonation needs CO₂ + moisture for weeks/months; without curing, doesn't gain strength. Mist regularly. 7. Cement substituted for lime in heritage repointing. Cement is rigid; old lime-bonded brick / stone moves with thermal cycles + slight settlement; cement mortar cracks the brick instead. Use compatible lime mortar. 8. Lime stabilisation without trial mix. Soil chemistry varies; lime dose for one site doesn't apply to another. Always trial-mix per IRC SP 70. 9. Sulphate-rich soil + lime = expansive ettringite. Heave damage. Test sulphate before lime treatment; use cement instead for sulphate-rich soils. 10. Lime in water-retaining structures (Class C / D). Class A is hydraulic; Class C is air-set. Don't substitute. For under-water curing, must be Class A. 11. Lime burns (worker safety). Quicklime + skin moisture → exothermic + caustic burn. PPE: gloves, eye protection, long sleeves; eyewash station nearby. 12. No reactivity test on slaked lime. After slaking, lime should be 'fat' (creamy putty); 'short' (gritty) lime is poor quality. Field test: rub between fingers; should be smooth, not gritty.

Lime usage in modern Indian construction:

1. Heritage / conservation: - Original mortar in pre-1900 buildings was lime-based (often hydraulic lime) - Modern repointing must be compatible — use Class A / B + sand mortar - Lime plaster restoration on heritage facades - Whitewash / colour wash on traditional finishes

2. Soil stabilisation: - Black cotton soil expanses (Maharashtra, Karnataka, MP, AP, TS) - 4-6 % lime addition stabilises subgrade - Used in road construction, runway construction, building plinth - Per IRC SP 70:2005

3. Compound (cement-lime) mortars: - 1:1:6 (cement:lime:sand) for breathable, flexible masonry mortar - More forgiving than straight cement-sand - Less prone to crack at cement-brick interface - Old construction practice; making a comeback in green building

4. Industrial / process: - Steel-making flux (pure CaO from quicklime) - Pulp + paper bleaching - Leather tanning - Sugar refining - Sewage treatment (pH adjustment, phosphate removal) - Drinking water treatment (post-clarification pH)

5. Lime-stabilised bricks (alternative to fired brick): - 5-10 % lime + soil + 5-10 % cement - Compressed manually or in mechanical press - Lower cost, lower carbon footprint vs fired brick - Used in low-cost rural housing, eco-villages

Modern alternatives that have displaced lime: - Portland cement: high-strength mortar (1:6 vs 1:3 lime) - AAC blocks: lighter, faster construction than brick + lime - Polymer-modified mortars: better adhesion, flexibility - Pre-mixed mortar bags: convenience

Trends: - Heritage segment growing (state heritage cells, ASI projects) - Eco-construction driving lime revival - Lime stabilisation in road construction is mature, growing

IS 712:1984 remains the technical baseline; modern revisions and supplementary IRC SP codes keep the practice current for specialised applications.