Code of practice for field slaking of building lime and preparation of putty

IS 1635: Scope & Related Specifications

• Scope: IS 1635 covers specifications for building limes used in construction, focusing on their quality, types, and testing methods.

• Related Standards:

  • IS 712:1984 — Specification for building limes (3rd revision) is a critical adjunct standard referenced for detailed lime quality and classification.

• Key Information for Planning Slaking Operation:

  • Lime type (quicklime or hydrated lime)
  • Purity and chemical composition
  • Moisture content
  • Particle size and reactivity
  • Slaking water quality and quantity

Typical Specifications from IS 712 (Summary):

Slaking Operation Planning:

• Use adequate water (about 2.5 times lime weight)
• Maintain temperature control to avoid overheating
• Ensure uniform mixing for complete hydration

flowchart LR
    Quicklime -->|Add water| Slaking
    Slaking -->|Heat + Reaction| Hydrated Lime
    Hydrated Lime -->|Cooling| Ready for Use

This ensures lime meets IS 712 & IS 1635 quality for construction use.

IS 1635 references important related standards, particularly for building lime specifications:

Key References in IS 1635:

• IS 712:1984 — Specification for Building Limes (3rd Revision)
• IS 1635:1992 (Reaffirmed 2003) — The main standard for Quicklime and Hydrated Lime

Important Specifications from IS 712 (Building Limes):

Typical Uses per IS 1635:

• Lime for mortar, plaster, and whitewashing
• Lime for soil stabilization

Quick Reference Formula for Lime Hydration:

[ CaO + H_2O \rightarrow Ca(OH)_2 + \text{heat} ]

This exothermic reaction is fundamental for lime setting and strength gain.

flowchart LR
    CaO[Quicklime (CaO)]
    H2O[Water (H₂O)]
    CaOH2[Hydrated Lime (Ca(OH)₂)]
    CaO -->|Add Water| CaOH2
    CaOH2 -->|Used in| Mortar & Plaster

For detailed chemical and physical properties, refer to IS 712 and IS 1635 tables.

IS 1635 references definitions and classifications from related standards:

• Definitions: Use terms as defined in IS 6508:1988 (Lime terminology).
• Classification of Lime: Refer to IS 712:1984 for lime types (e.g., quicklime, hydrated lime).

Key points for slaking operation planning (Clause 4):

• Quantity and type of lime
• Water required for slaking
• Duration and method of slaking
• Temperature control during slaking

Summary of Lime Classification (from IS 712:1984):

Typical Slaking Reaction:

[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{Heat} ]

For detailed definitions and specifications, consult IS 6508 and IS 712 alongside IS 1635.

IS 1635 - Necessary Information for Slaking Quicklime

Key Points from IS 1635:

• Slaking Methods:

  • Tank Slaking (Clause 6.2.1): Add lime to water in a watertight tank lined with lime-resistant material (brick lining recommended).
    • Produces lime putty directly.
    • Tank must be large enough for thorough stirring.
  • Platform Slaking (Clause 6.2.2): Add water to lime on a platform (less desirable).

• Importance:

  • Proper slaking ensures complete hydration of quicklime.
  • Prevents defects in mortar/plaster and reduces maintenance.

Specifications & Recommendations:

Practical Tips:

• Always add lime to water in tank slaking to avoid dry pockets.
• Use brick-lined tanks to resist lime's corrosive nature.
• Ensure complete slaking to avoid weak mortar/plaster.

flowchart LR
    A[Quicklime] --> B{Slaking Method}
    B --> C[Tank Slaking: Add Lime to Water]
    B --> D[Platform Slaking: Add Water to Lime]
    C --> E[Lime Putty]
    D --> F[Partially Hydrated Lime]
    E --> G[Good Mortar/Plaster Quality]
    F --> H[Defects & Maintenance Issues]

This approach ensures sound construction and durability of lime-based materials.

IS 1635: Storage of Quicklime Before Slaking - Key Points

• Quicklime Storage:

  • Must be kept dry; no contact with water allowed during storage, handling, or transit (Clause 8.1).
  • Stored in a water-tight, covered place to prevent moisture ingress and fire hazard.

• Slaking Preparation (Clause 6.2.2.1):

  • Spread quicklime in 150 mm thick layers on a water-tight masonry platform.
  • Water is sprinkled in small quantities gradually until lime disintegrates into fine powder.
  • Heap turned over repeatedly to ensure uniform slaking.
  • Slaking continues about 24 hours.
  • Resulting slaked lime is screened through a 3.35 mm IS sieve.
  • Store slaked lime in a dry, covered place or pack in polyethylene-lined gunny bags.

• Putty Preparation (Clause 6.2.2.1):

  • Add dry slaked lime to water, stir to thick cream consistency.
  • Maturation period:
    • ≥16 hours for Class C & D limes.
    • ≤12 hours for Class B & F limes.

Quicklime Slaking Summary Table

flowchart TD
    A[Quicklime Storage] --> B[Spread in 150 mm layer]
    B --> C[Sprinkle water gradually]
    C --> D[Turn heap repeatedly]
    D --> E[Slaking for ~24 hours]
    E --> F[Screen through 3.35 mm sieve]
    F --> G[Store slaked lime dry or pack]

Note: Always ensure quicklime is stored away from moisture to avoid hazardous reactions.

IS 1635: Slaking Quicklime & Preparation of Putty

1. Slaking Quicklime (Clause 6.2.2.1)

• Method:
  • Spread quicklime in a 150 mm thick layer on a water-tight masonry platform.
  • Sprinkle water gradually until lime disintegrates into fine powder.
  • Turn heap repeatedly; add minimum water needed.
  • Allow slaking to continue for about 24 hours.
  • Screen through 3.35 mm IS Sieve.
  • Store in dry, covered place or polyethylene-lined gunny bags.

2. Preparation of Putty (Clause 6.2.2.1)

• Add dry slaked lime to water.
• Stir to thick cream consistency.
• Maturation time before use:
  • Class C & D limes: ≥ 16 hours
  • Class B & F limes: ≤ 12 hours

3. Tank Slaking (Clause 6.2.1)

• Add lime to water in a water-tight tank.
• Tank lined with lime-resistant material (brick lining recommended).
• Produces lime putty directly.
• Suitable when putty form is required.

Summary Table:

flowchart TD
    A[Quicklime] --> B[Spread on platform (150 mm thick)]
    B --> C[Sprinkle water gradually]
    C --> D[Turn heap repeatedly]
    D --> E[Slaking for ~24 hours]
    E --> F[Screen through 3.35 mm sieve]
    F --> G[Dry hydrated lime powder]
    G --> H[Add water + stir]
    H --> I[Putty maturation (12-16 hrs)]
    I --> J[Ready lime putty]

**

IS 1635 - Preliminary Cleaning (Clause 6.1)

• Purpose: Remove all unslaked lime stones and residual materials from previous slaking to ensure clean, uncontaminated lime slaking.
• Procedure:
  • Clean the slaking receptacle or platform thoroughly before starting.
  • Remove all lumps, dust, and foreign matter.
• Reason: Prevent contamination and ensure uniform slaking reaction.

Additional Notes (from general practice):

• Slaking ratio: Typically, quicklime to water ratio is about 1:2 to 1:3 by weight.
• Temperature: Slaking is exothermic; temperature can rise up to 80-100°C.
• Time: Slaking time varies but usually 30 minutes to 1 hour for complete hydration.

Summary Table: Preliminary Cleaning Checklist

flowchart TD
    A[Start] --> B[Clean Slaking Receptacle]
    B --> C[Remove Unslaked Lime]
    C --> D[Remove Residual Materials]
    D --> E[Inspect for Cleanliness]
    E --> F[Ready for Slaking Operation]

For detailed slaking procedures, refer to Clause 6.2 and related IS standards.

IS 1635 - Slaking Procedure (Clause 6.2)

Key Points on Slaking:

• Slaking Methods:

  • Tank Slaking (6.2.1): Add lime to water.
    • Produces lime putty directly.
    • Preferred method for quality and completeness.
    • Tank must be:
      • Water-tight
      • Large enough for stirring
      • Lined with lime-resistant material (brick lining recommended)
  • Platform Slaking (6.2.2): Add water to lime (less desirable).

• Purpose:

  • Proper slaking is critical to avoid defects in mortar/plaster.
  • Ensures complete hydration of quicklime for sound construction.

Practical Notes:

Summary Flow:

flowchart TD
    A[Quicklime] --> B{Slaking Method}
    B -->|Tank Slaking| C[Lime added to Water]
    B -->|Platform Slaking| D[Water added to Lime]
    C --> E[Lime Putty (Preferred)]
    D --> F[Slaked Lime (Less uniform)]

Ensure complete slaking to prevent mortar/plaster defects and guarantee durability.

IS 1635 - Tank Slaking Key Points

Tank Slaking Method (Clause 6.2.1)

• Lime is added to water in a water-tight tank.
• Tank must be lined with lime-resistant material, preferably brick lining.
• Tank size should allow adequate stirring of the lime-water mix.
• Produces lime putty directly, ideal when putty is the required product.

Continuous Slaking Setup (Clause 6.2.1.1)

• Use two tanks:
  • Upper tank: 400 mm deep, above ground for continuous slaking of quicklime.
  • Lower tank: 750-800 mm deep, below ground for settling and maturing lime putty.
• Milk of lime flows through a 3.35 mm IS sieve (per IS 460 Part 1:1985) from upper to lower tank.
• Sieve must be cleaned regularly to avoid clogging.
• Two lower tanks can be used alternatively to ensure continuous supply.

Summary Table

flowchart TD
    A[Quicklime + Water] --> B[Upper Tank (400 mm)]
    B -->|Milk of Lime| C[3.35 mm IS Sieve]
    C --> D[Lower Tank (750-800 mm)]
    D --> E[Lime Putty Maturation]
    E --> F[Use Lime Putty]

This arrangement ensures continuous slaking with proper settling and maturation of lime putty.

IS 1635 - Platform Slaking (Clause 6.2.2)

Key Points on Platform Slaking:

• Method: Add water to lime on a platform.
• Purpose: To slake quicklime by controlled addition of water.
• Note: Platform slaking is less desirable than tank slaking due to difficulty in achieving uniform slaking.
• Platform Requirements:
  • Should be waterproof and non-reactive with lime.
  • Large enough to allow thorough mixing and slaking.
  • Usually constructed with brick or concrete with a protective lining.

Specifications:

Important Notes:

• Platform slaking produces hydrated lime but may have non-uniform quality.
• Tank slaking (Clause 6.2.1) is preferred for lime putty production.
• Proper slaking ensures better workability and strength of lime products.

flowchart TD
    A[Quicklime on Platform] --> B[Add Water Gradually]
    B --> C[Mix Continuously]
    C --> D{Fully Slaked?}
    D -- No --> B
    D -- Yes --> E[Hydrated Lime Ready]

For detailed design, refer to IS 1635 Clause 6.2 and ensure platform integrity and safety during slaking.

IS 1635: Preparation of Lime Putty (Class B, C, D, F)

Key Points from IS 1635 (Clause 6 & 7.2)

• Slaking of Quicklime: Quicklime is slaked by adding water gradually until complete hydration.
• Putty Preparation: Lime putty is prepared by thorough mixing of slaked lime with water to form a smooth, creamy paste.
• Storage: Lime putty must be stored under water to prevent carbonation and drying.
• Usage: Use the putty as soon as possible after preparation for best results.

Typical Specifications & Guidelines

Important Notes

• Avoid quick drying; keep submerged to maintain workability.
• Use within a few days; older putty improves workability but may lose activity.
• Proper slaking ensures better plasticity and durability of lime mortar/plaster.

flowchart LR
    A[Quicklime] --> B[Add Water Gradually]
    B --> C[Slaking (24-48 hrs)]
    C --> D[Mix to form Putty]
    D --> E[Store Under Water]
    E --> F[Use Putty ASAP]

This ensures a high-quality lime putty suitable for masonry and plastering works as per IS 1635.

IS 1635: Storage of Building Lime After Slaking

Key Specifications & Procedures

• Slaking Quicklime to Dry Hydrated Lime (Clause 6.2.2.1):

  • Spread quicklime in a 150 mm thick layer on a water-tight masonry platform.
  • Sprinkle water gradually until lime disintegrates into fine powder.
  • Turn heap repeatedly; add minimum water required.
  • Allow slaking for about 24 hours.
  • Screen through 3.35 mm IS Sieve.
  • Store slaked lime dry and covered, or pack in polyethylene-lined gunny bags.

• Storage of Dry Slaked Lime (Clause 7.1):

  • For short term (few days): Store on platform, protected from rain and wind.
  • For long term (up to 2 months): Bag in polyethylene-lined gunny bags, stitched properly, and keep in a dry, closed godown.

• Putty Preparation (Clause 6.2.2.1):

  • Mix dry slaked lime with water to thick cream consistency.
  • Maturation time:
    • Class C & D lime: ≥16 hours
    • Class B & F lime: ≤12 hours

• Continuous Slaking Setup (Clause 6.2.1.1):

  • Two tanks:
    • Upper tank: 400 mm deep, above ground for continuous slaking.
    • Lower tank: 750-800 mm deep, below ground for settling and maturing putty.
  • Milk of lime passes through 3.35 mm IS Sieve into lower tank.
  • Two lower tanks may be used alternately for continuous supply.

Summary Table: Lime Storage & Handling

IS 1635: Precautions During Slaking and Handling of Quicklime

Key Points from IS 1635:

• Slaking Reaction: Quicklime (CaO) reacts violently with water, releasing a large amount of heat (exothermic reaction).
• Fire Hazard: Due to heat release, fire precautions must be strictly followed during slaking.
• Storage: Quicklime must be kept dry; no contact with moisture during storage, handling, or transit.
• Slaking Procedure: Controlled addition of water to quicklime is essential to avoid splattering and excessive heat.

Important Specifications & Precautions:

Reaction Formula:

[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{Heat} ]

• Heat released: approx. 65 kcal per mole of CaO slaked.

Summary Diagram:

flowchart LR
    A[Quicklime (CaO)] -->|Add water slowly| B[Slaking Reaction]
    B --> C[Calcium Hydroxide Ca(OH)2]
    B --> D[Heat Released (Exothermic)]
    D --> E[Fire Hazard Precautions]
    A --> F[Dry Storage & Handling]

Always ensure controlled slaking to prevent accidents and maintain quality of hydrated lime.

IS 1635: Fire Hazard Precautions for Quicklime

Key Points from Clauses 8.1 & 8.5

• Clause 8.1:

  • Quicklime reacts violently with water during slaking, releasing significant heat.
  • Precaution: Avoid any contact of quicklime with water during storage, handling, or transit to prevent fire hazards.

• Clause 8.5 (Table 8 - Precautions):

  • Freshly slaked lime is hot and can cause skin burns.
  • Workmen handling milk of lime should oil their skin daily to prevent skin cracks and infections.

Summary Table: Fire Hazard Precautions

Additional Recommendations (Engineering Practice):

• Store quicklime in dry, moisture-proof containers.
• Use personal protective equipment (PPE): gloves, goggles, and protective clothing.
• Ensure adequate ventilation in slaking areas to dissipate heat.
• Train workers on safe handling procedures and emergency response.

flowchart TD
    A[Quicklime Storage] -->|No Water Contact| B[Handling & Transit]
    B --> C[Slaking Process]
    C -->|Heat & Reaction| D[Fire Hazard]
    D --> E[Precautions]
    E --> F[Oil Skin for Workers]
    E --> G[Use PPE]
    E --> H[Dry Storage]

Note: IS 1635 emphasizes strict control of moisture exposure to prevent fire hazards and personal injury during quicklime handling and slaking.

IS 1635 — Dust and Respiratory Protection Key Points

Protection from Lime Dust (Clauses 8.2 to 8.5)

• Eye Protection: Use goggles to prevent irritation from lime dust.
• Respiratory Protection: Use suitable respirators to protect nose, throat, and lungs from inhaling lime dust.
• Skin Protection:
  • Quicklime can cause burns, especially on moist skin.
  • Use rubber gloves, gum boots, and skin-protecting creams.
  • Workers should oil their skin daily when working with hot slaked lime to prevent cracks and infections.
• Hygiene: Wash face and skin with fresh water immediately after exposure to lime dust to reduce irritation.

Summary Table (Clause 8.5 Precautions)

Additional Notes

• No explicit formulas or numerical tables are provided in IS 1635 for dust protection.
• Respirators should comply with relevant respiratory protection standards (e.g., NIOSH or IS standards for particulate filters).
• Skin creams and protective gear must be selected based on local climate (warm/humid conditions increase risk).

flowchart LR
    A[Lime Dust Exposure] --> B{Hazard Type}
    B -->|Inhalation| C[Goggles + Respirators]
    B -->|Skin Contact| D[Rubber Gloves + Gum Boots + Skin Cream]
    B -->|Hot Slaked Lime| E[Daily Skin Oiling]
    B -->|Eye Irritation| C
    F[Post Exposure] --> G[Wash with Fresh Water]

Ensure strict adherence to these precautions to maintain worker safety when handling lime materials.