Code of practice for the application of cement and cement-lime plaster finishes

IS 1661: Scope & Key Specifications Summary

• Scope (Clause 6.2):
  Scaffolding materials (wooden ballies, bamboos, planks, trestles) must be sound, comply with local regulations, and be inspected before use.

• Design Considerations (Clause 7):
  Tools/accessories definitions per IS 1630-1960.

• Plaster Specifications (Clause 7.4.1.1):
  Weight of hydrated lime in putty:
  [ W_h = G \times \frac{T}{W_p - 1000} ]
  Where:

  • (W_h) = weight of dry hydrate (kg/m³)
  • (G) = specific gravity of hydrate (IS 2394-1965)
  • (W_p) = weight of putty (kg/m³)
  • (T) = (context suggests a term related to lime content)

• Table 1: Background Data for Internal Plastering
  Key points:

  • Dense clay bricks: negligible shrinkage, low suction, may need bonding agents or wire mesh.
  • Normal bricks: moderate suction, rake joints recommended.
  • Dense concrete: variable shrinkage, low suction, use bonding treatments if no key.
  • No-fines concrete: low to moderate shrinkage, good key, no special treatment needed.

flowchart TD
  A[Scaffolding Materials] --> B[Inspection & Compliance]
  C[Plastering] --> D[Determine Lime Content]
  D --> E[Use formula for \(W_h\)]
  F[Surface Types] --> G[Preparation Methods]
  G --> H[Spatterdash, Bonding Agents, Wire Mesh]

Note: Refer IS 1661 full text for detailed tables and exact formula parameters.

IS 1661 - Key Definitions, Formulas & Tables Summary

1. Definitions (Clause 2.0 & 2.2)

• Tools & Accessories (e.g., trowels, floats, rules) are defined as per IS 1630-1960.

2. Key Formula for Hydrated Lime Content (Clause 7.4.1.1)

[ W_h = \frac{G - T(W_2 - 1000)}{G} ]

Where:

• (W_h) = Weight of dry hydrate (kg/m³)
• (G) = Specific gravity of hydrate (see IS 2394-1965)
• (W_p) = Weight of putty (kg/m³)

3. Recommended Plaster Specifications (Table 7.4)

4. Surface Preparation & Characteristics (Summary from Table 1)

• Dense clay bricks: Low suction, poor key → Use spatterdash, bonding agents, or wire mesh.
• Normal clay bricks: Moderate to high suction → Rake joints.
• Dense concrete: Low suction, poor key → Use bonding treatments.
• No-fines concrete: Low suction, good key → No special treatment needed.

flowchart TD
    A[Surface Type] --> B{Suction Level}
    B -->|Low| C[Use bonding agents or sp

IS 1661 Key Materials Specifications & Formulas

1. Materials as per Clause 4.1

• Cement: IS 269-1967 or IS 455-1967
• Lime: Class B & C as per IS 712-1964
• Sand: IS 1542-1960

2. Lime Putty Weight Formula (Clause 7.4.1.1)

To find the weight of hydrated lime (Wh) in putty:

[ Wh = G \times \left( \frac{W_p - W_n}{1000} \right) ]

Where:

• (W_n) = Weight of dry hydrate (kg/m³)
• (G) = Specific gravity of hydrate (see IS 2394-1965)
• (W_p) = Weight of putty (kg/m³)

3. Table 1: Summary of Background Data for Internal Plastering (Key Points)

4. Additional Notes

• Scaffolding materials must be sound and inspected (Clause 6.2).
• Surface preparation varies by substrate for optimal plaster adhesion.

flowchart TD
    A[Materials] --> B[Cement (IS 269/455)]
    A --> C[Lime (IS 712)]
    A --> D[Sand (IS 1542)]
    E[Lime Putty Weight] --> F[Formula: Wh = G × (Wp - Wn)/1000]
    G[Surface Types] --> H[Dense clay bricks]
    G --> I[Normal clay bricks]
    G --> J[Dense concrete]
    G --> K[No-fines concrete]

This

IS 1661: Requirements for Materials in Plastering

Key Formulas

• Weight of Hydrated Lime in Putty (Clause 7.4.1.1):

  [ W_h = \frac{G - T(W_2 - 1000)}{G} ]

  Where:

  • (W_h) = weight of dry hydrate (kg/m³)
  • (G) = specific gravity of hydrate (IS:2394)
  • (W_p) = weight of putty (kg/m³)

Material Specifications (Clause 4.1)

• Cement: IS 269-1967 or IS 455-1967
• Lime: Class B & C, IS 712-1964
• Sand: IS 1542-1960

Surface Preparation & Characteristics (Summary from Table 1)

Recommended Plaster Mix Proportions & Thickness (Table 2)

IS 1661: Storage and Handling of Materials - Key Points

Storage of Cement (Clause 5.1)

• Store cement off the ground, under cover, and away from damp surfaces.
• Prevent moisture intrusion and contamination to avoid deterioration.
• Refer IS:4082-1967 for detailed cement storage guidelines.

Scaffolding Materials (Clause 6.2)

• Wooden ballies, bamboos, planks, trestles must be sound and comply with local building codes.
• Materials should be inspected before use.

Lime Putty Weight Formula (Clause 7.4.1.1)

To find weight of dry hydrated lime (Wh) in putty: [ Wh = G \times \frac{T}{(W_p - 1000)} ] Where:

• (Wh) = weight of dry hydrate (kg/m³)
• (G) = specific gravity of hydrate (IS:2394-1965)
• (W_p) = weight of putty (kg/m³)
• (T) = (contextual factor, check IS for exact meaning)

Surface Preparation for Plaster (Table 7.4.1.1 Summary)

Summary Diagram: Material Storage & Handling Flow

flowchart TD
    A[Materials Received] --> B{Inspect Quality}
    B -->|Sound & Compliant| C[Store Properly]
    B -->|Defective| D[Reject or Repair]
    C --> E{Material Type}
    E -->|Cement| F[Store off ground, dry place]
    E -->|Scaffolding| G[Check soundness, local code]
    E -->|Plaster| H[Prepare surface as per Table]

Note: Always refer to IS 4082

Care of Tools and Accessories — IS 1661 Key Points

• Cleaning Frequency (Clause 6.1):

  • Clean tools by scraping and washing daily or after use with different materials.
  • Metal tools must be cleaned and greased after each operation to prevent rusting.

• Inspection:

  • Examine and clean all tools thoroughly before starting plastering to avoid contamination.

• Importance of Cleanliness:

  • Essential for cement plasters to prevent set material contamination, which can degrade tool life and plaster quality.

• Reference Standards:

  • Tools and accessories definitions/specifications conform to IS 1630-1960 (Mason’s tools for plaster and pointing work).

• Storage of Sand (Clause 5.3):

  • Store sand under clean conditions to avoid contamination by soil or deleterious substances.

Summary Table: Tool Care Routine

flowchart TD
    A[End of Day / After Use] --> B[Scrape & Wash Tools]
    B --> C{Metal Tools?}
    C -- Yes --> D[Clean & Grease]
    C -- No --> E[Store Properly]
    D --> E
    E --> F[Inspect Before Next Use]

Note: Follow IS 1630 for detailed tool specifications and maintenance practices.

Suitability of Cement-Lime Mixes (IS 1661 Clause 7.1 & 7.1.1)

• Cement-lime mixes with lime putty, dry hydrated lime, cement, and sand offer high workability and ease of application.
• Increasing cement proportion reduces workability.
• Cement-lime plaster is prepared by dry mixing cement and sand, then adding lime putty with water (Clause 11.2.1).

Key Formula to Determine Weight of Hydrated Lime in Putty (Clause 7.4.1.1)

[ W_h = \frac{G \times T}{(W_p - 1000)} ]

Where:

• (W_h) = Weight of dry hydrated lime (kg/m³)
• (G) = Specific gravity of hydrated lime (per IS 2394-1965)
• (T) = (Not fully detailed in snippet, typically related to lime content)
• (W_p) = Weight of putty (kg/m³)

Recommended Plaster Specifications (Summary from Table 7.4 & Clause 7.2.2.1)

Notes:

• Lime putty enhances workability and bonding.
• Surface preparation is critical for plaster adhesion and durability.
• Use bonding treatments or spatterdash coats where key is poor.

flowchart TD
    A[Cement + Sand (Dry Mix)] --> B[Add Lime Putty + Water]
    B --> C[Mix Thoroughly

IS 1661: Application Procedures and Control Measures for Plastering

Key Formulas:

• Weight of dry hydrate in putty (Clause 7.4.1.1):

[ W_h = G \times \left( \frac{W_p - 1000}{W_p} \right) ]

Where:

• ( W_h ) = weight of dry hydrate (kg/m³)
• ( G ) = specific gravity of hydrate (from IS:2394-1965)
• ( W_p ) = weight of putty (kg/m³)

Important Table (Clause 7.2.2.1 & 7.4.1.1):

Control Measures:

• Ensure substrate is dry to reduce efflorescence.
• Use bonding agents or spatterdash coats on surfaces with poor key.
• Wire mesh should be fixed with a minimum 6 mm clearance.
• Adjust plaster mix and application based on substrate suction and surface characteristics.

flowchart TD
    A[Substrate Type] --> B{Surface Suction}
    B -->|Low| C[Use Bonding Agent or Spatterdash]
    B -->|Moderate/High| D

Preliminary Programming of Work (IS 1661)

Key Specifications & Guidelines

• Clause 8.5: Maintenance of Proper Time Intervals

  • Drying shrinkage of the first coat must be substantially complete before applying the next.
  • Time interval:
    • Summer: Minimum 1 day
    • Winter: Minimum 2 days
  • Keep the surface damp during this period to prevent premature drying and cracking.
  • Proper intervals reduce efflorescence and map crazing on plaster surfaces.

• Clause 6.2: Scaffolding

  • Use sound wooden ballies, bamboos, planks, trestles.
  • Follow local regulations.
  • Inspect scaffolding before use.

• Clause 7.4.1.1: Lime Putty Weight Calculation

  [ W_h = G \times \frac{T (W_2 - 1000)}{G} ]

  Where:

  • (W_h) = weight of dry hydrate (kg/m³)
  • (G) = specific gravity of hydrate (IS:2394-1965)
  • (T) = weight of putty (kg/m³)
  • (W_2) = water content in putty

• Table 1: Background Data for Internal Plastering

flowchart TD
    A[Apply First Coat] --> B[Allow Drying]
    B -->|Summer: 1 day| C[Keep Surface Damp]
    B -->|Winter: 2 days| C
   

IS 1661: Surface Preparation for In Situ Concrete (Clause 12.3)

• Surface Roughness (12.3.2):
  Concrete surfaces must be rough enough for good adhesion. Roughening is typically done by hacking or wire brushing to expose aggregate, enhancing mechanical key.

• Surface Cleaning (12.3.1):
  Remove dust, loose particles, oil, or laitance. Use wire brushes, water jets, or air blasting as per Clauses 12.1.1 & 12.1.2.

• Surface Moisture (12.3.2):
  Surfaces should be evenly wetted but not saturated to achieve correct suction. This prevents premature drying and ensures bond strength.

Key Specifications Summary:

Practical Notes:

• Suction Control: Avoid dry or overly wet surfaces; maintain a damp surface for optimum plaster bond.
• Surface Profile: Roughness depth ~1-2 mm is effective for plaster adhesion.

flowchart LR
    A[Concrete Surface] --> B[Clean (remove dust, oil)]
    B --> C[Roughen (expose aggregate)]
    C --> D[Moisten (damp, not saturated)]
    D --> E[Apply plaster for strong adhesion]

This ensures durable plaster bonding per IS 1661 guidelines.

IS 1661 - Proportioning and Mixing of Plaster

Key Specifications (Clause 7.3.3, Table 7.4)

Notes:

• Sand grading: For undercoats, use coarse sand conforming to IS 383 Zone II, fineness modulus ≥ 2.0.
• Single coat plaster sand: Fineness modulus ~1.5, conforming to IS 383 Zone IV.
• Mix flexibility: Adjust mixes based on sand quality, maintaining strength.

Formula for Hydrated Lime Weight in Putty (Clause 7.4.1.1)

[ W_h = G - T \times \frac{(W_2 - 1000)}{G} ]

• (W_h) = Weight of dry hydrate (kg/m³)
• (G) = Specific gravity of hydrate (IS 2394)
• (W_p) = Weight of putty (kg/m³)

Summary Diagram

IS 1661: Preparation of Backgrounds for Internal Plastering

Key Points from IS 1661

1. Background Data Summary (Table 1, Clause 7.2.2.1)

2. Durability & Bonding (Clause 12.1)

• Good bond between background and first plaster coat is vital.
• Background must be prepared as per Clauses 12.2 to 12.4 depending on material.
• Suction (Clause 2.5.3) affects water absorption and bonding.

3. Lime Putty Weight Formula (Clause 7.4.1.1)

To determine weight of hydrated lime in putty:

[ W_h = G \times \left(1 - \frac{T(W_p - 1000)}{G}\right) ]

Where:

• ( W_h ) = weight of dry hydrate (kg/m³)
• ( G ) = specific gravity of hydrate (IS:2394)
• ( W_p ) = weight of putty (kg/m³)

Summary

• Background preparation depends on type and suction characteristics.
• Use spatterdash coats or bonding agents for poor key surfaces.
• Ensure dry surfaces to minimize efflorescence.
• Follow manufacturer guidelines for special plasters and bonding treatments.

flowchart TD
    A[Background Type] -->

IS 1661: Rendering or First Coat - Key Specifications

Rendering (First Coat) - Clause 13.1.1

• Thickness: 10 to 15 mm
• Coverage: Full wall length or natural breaks (doors/windows)
• Surface Prep: Roughen before hardening to provide mechanical key for next coat

Floating (Second Coat) - Clause 13.2

• Thickness: 3 to 8 mm
• Surface Prep: Dampen first coat evenly, then roughen after application
• Curing: Damp-cure each undercoat for at least 2 days

Recommended Plaster Mix & Thickness (Table 7.4 from Clause 7.3.3)

Notes:

• Use coarse sand conforming to IS 383:1970 Zone II, fineness modulus ≥ 2.0 for undercoats.
• Roughening after each coat ensures mechanical bonding.
• Proper damp curing improves plaster durability.

flowchart TD
    A[Wall Surface] --> B[Rendering Coat (10-15 mm)]
    B --> C[Roughen Surface]
    C --> D[Second Coat (3-8 mm)]
    D --> E[Roughen Surface]
    E --> F[Finishing Coat (3-5 mm)]

This ensures a durable plaster finish with good bonding between coats.

IS 1661: Finishing Coat and Textures – Key Points

1. Plaster Coat Specifications (Clause 7.3.3, Table 7.4)

• Note: Undercoats should use coarse sand (grading zone II, IS 383) with fineness modulus ≥ 2.0.

2. Thickness of Finishing Coat (Clause 7.3.1)

• Minimum thickness just enough to harden satisfactorily (typically 3–8 mm).

3. Special Finishing Textures (Clause 14.3)

• Use special tools for final coat application.
• Follow IS 2402-1963 for detailed texture finishes.

4. Hydrated Lime Content Formula (Clause 7.4.1.1)

[ W_h = \frac{G - T(W_p - 1000)}{G} ]

• (W_h): Weight of dry hydrate (kg

Trueness of Plastering System (IS 1661 Highlights)

1. Trueness & Surface Preparation (Clause 15 & 7.2.2.1)

• Trueness depends on substrate type (brick, concrete, no-fines concrete).
• Surface key and suction affect plaster adhesion.
• Use spatterdash coats, bonding agents, or wire mesh for poor key surfaces.
• Wire mesh should be fixed ≥ 6 mm clear from surface.

2. Recommended Plaster Specifications (Clause 7.4, Table 2)

• Coarse sand for undercoats should conform to IS 383 Zone II, fineness modulus ≥ 2.0.

3. Hydrated Lime Content Formula (Clause 7.4.1.1)

[ W_h = \frac{G - T (W_2 - 1000)}{G} ]

Where:

• (W_h) = Weight of dry hydrate (kg/m³)
• (G) = Specific gravity of hydrate (IS 2394)
• (W_p) = Weight of putty (kg/m³)

Summary Diagram of Plastering Layers

graph TD
  A[