Code of Practice for External Rendered Finishes

IS 2402 - Foreword Summary & Key Specifications

The Foreword of IS 2402 (Code of Practice for External Rendered Finishes) introduces the standard, its scope, and committee members. It sets the foundation for external rendering practices in construction.

Key Points from Foreword & Related Sections:

• Purpose: Standardizes external rendered finishes for concrete/plaster surfaces.
• Scope: Covers materials, tools, application methods, design considerations, and maintenance.
• Terminology: Defined in Clause 2.0 for clarity.
• Design Considerations (Clause 6):
  • Functions of external renderings: protection, aesthetics, durability.
  • Suitability of finishes based on background nature.
  • Resistance to water penetration, cracking, and fire.
  • Recommended mix proportions and number of coats.
• Application (Clause 8):
  • First undercoat, subsequent coats, finishing coats (plain, textured, roughcast, dry-dash).
  • Use of metal lathing as backing (Clause 7.5).

Typical Recommended Mix Proportions (Clause 6.11):

Functions of Rendering Coats:

flowchart LR
    A[External Rendered Finish] --> B[Undercoat]
    B --> C[Subsequent Undercoat]
    C --> D[Finishing Coat]
    D --> E[Protection & Aesthetic]

Summary:

• Follow IS 2402 for material selection, mix proportions, number & thickness of coats, and application techniques.
• Ensure proper curing and maintenance for durability.
• Use metal lathing where required for better adhesion.

For detailed tables and procedures, refer to clauses 6, 7, and 8 in IS 2402.

IS 2402: Scope Summary

• Scope (Clause 1): This standard covers the code of practice for external rendered finishes on buildings, including materials, application, and design considerations for durability, water resistance, thermal properties, and aesthetics.

• Key Aspects Included:

  • Types of external finishes (plaster, concrete, tiles)
  • Suitability of finishes based on background surface (Clause 6.3)
  • Resistance to water penetration, cracking, crazing (Clauses 6.4, 6.6, 6.7)
  • Thermal and sound insulation properties (Clauses 6.8, 6.9)
  • Fire resistance (Clause 6.10)
  • Recommended mix proportions for mortar (Clause 6.11)
  • Number and thickness of coats for finishes (Clauses 6.12, 6.13)

Recommended Mix Proportions (Typical example from Clause 6.11):

Functions & Thickness of Coats (Clause 6.13):

flowchart LR
    A[Background Surface] --> B[Scratch Coat]
    B --> C[Brown Coat]
    C --> D[Finish Coat]
    D --> E[External Rendered Finish]

This scope ensures durability, aesthetics, and performance of external finishes per IS 2402.

IS 2402 - Terminology (Clause 2.0 & 2.1) Key Definitions

• Background: The material or materials to which the first rendering coat is applied.
• Eflorescence: Salt deposits on the surface of building materials as they dry.
• Firring: Lightweight battens (wood/metal) fixed to backgrounds for attaching metal or sheet materials.
• Key: Surface indentations or grooves that allow rendering material to bond mechanically.
• Thickness of a Coat: Average thickness of a rendering coat excluding material used for leveling or filling joints.
• Workability: Quality of rendering mix affecting application ease, influenced by flow, cohesiveness, and moisture retention.

Summary Table of Key Terms

This terminology sets the foundation for understanding rendering practices per IS 2402. For detailed mix proportions, coat thickness, and finishing suitability, refer to Clauses 6.11, 6.13, and Table I respectively.

flowchart TD
    A[Background] --> B[First Coat of Rendering]
    B --> C[Thickness of Coat]
    B --> D[Workability]
    B --> E[Key (Indentations)]
    F[Firring] --> A
    G[Eflorescence] -.-> B

This diagram shows relationships between background, rendering coats, and key terminology.

IS 2402: Necessary Information for External Rendered Finishes (Clause 3)

For proper selection, preparation, and application of rendering, the following key information must be provided:

• Surface Type: Brick, stone, concrete, etc. Construction details must suit the background, including preparation extent.
• Area & Type of Finish: Specify the external rendered finish area and type.
• Background Nature:
  • Presence of soluble sulphates.
  • Age of background (to assess drying time before rendering).
• Atmospheric Conditions: Dust, acidic fumes, exposure to rain/wind.
• Drawings: Details at junctions (doors, windows), cornices, arrises, returns.
• Decorative Finishes: Details of finishes over the rendering.

Table II: Backgrounds for Renderings (Clause 6.3.2)

Additional Notes on Water Penetration (Clause 6.4.1)

• Water penetrates via pores or cracks.
• Penetration depends on:
  • Permeability of coats.
  • Suction difference between rendering and backing.
  • Quantity of water on surface.

This concise framework ensures durable, effective external finishes by addressing materials, environment, and detailing.

IS 2402: Materials, Tools and Accessories for External Rendered Finishes

Tools and Accessories (Clause 4.9 & 5.2)

• Tools should conform to IS 1630-1960 (Mason's Tools for Plaster Work).
• Clean tools daily by scraping and washing, especially when switching materials.
• Metal tools: clean and grease after each use to prevent contamination.
• Tools must be clean before plastering starts to ensure quality and durability.

Materials (General from IS 2402)

• Use quality cement, sand, lime, and additives as per IS specifications.
• Metal lathing types (Fig. 6) for reinforcement:
  • 6A: Plain Expanded Type
  • 6B: Ribbed Expanded Type (integral ribs)
  • 6C: Ribbed Expanded Type (ribs attached post-expansion)
  • 6D: Perforated Type

Recommended Mix Proportions (from Clause 6.11)

Care Tips

• Avoid contamination with set material.
• Regular inspection and maintenance of tools increase lifespan and quality of finish.

flowchart TD
    A[Materials] --> B[Quality Cement, Sand, Lime]
    A --> C[Metal Lathing Types]
    B --> D[Mix Proportions]
    C --> E[Expanded, Ribbed, Perforated Types]
    F[Tools] --> G[Conform to IS 1630]
    F --> H[Clean & Grease Regularly]
    H --> I[Prevents Contamination]

Summary: Use IS 1630-compliant tools, maintain cleanliness, employ recommended mortar mixes, and select appropriate metal lathings for durable external renders per IS 2402.

IS 2402: Care of Materials, Tools, and Accessories – Key Points

Tools and Accessories (Clause 4.9 & 5.2)

• Tools should conform to IS 1630-1960 (Mason's Tools for Plaster Work).
• After each day's work or when switching materials:
  • Clean tools by scraping and washing.
  • Metal tools must be cleaned and greased after use to prevent rust and ensure longevity.
• Before plastering starts, tools must be thoroughly cleaned to avoid contamination, especially critical for cement plasters.

Materials (Clause 5.1)

• Store and handle materials per their respective specifications (refer to Clause 4).
• Proper storage prevents contamination and deterioration.

Coordination (Clause 3.3)

• Ensure effective communication and coordination among all workers involved in rendering and related activities to maintain quality and workflow.

Summary Table for Tool Care

Typical Metal Lathing Types (Fig.6)

• 6A: Plain Expanded
• 6B: Ribbed Expanded (integral ribs)
• 6C: Ribbed Expanded (ribs attached later)
• 6D: Perforated

flowchart TD
    A[Start of Work] --> B[Check & Clean Tools]
    B --> C{Tools Metal?}
    C -- Yes --> D[Clean & Grease Tools]
    C -- No --> E[Scrape & Wash Tools]
    D --> F[Store Properly]
    E --> F
    F --> G[Use Tools for Plastering]
    G --> H[End of Day or Material Change]
    H --> B

This ensures tools remain effective and materials uncontaminated per IS 2402 standards.

IS 2402: Design Considerations for External Rendered Finishes

Key Points from Clause 6.2.2 and Table I

• Scraped/Textured Finishes:

  • Less prone to cracking and crazing than smooth finishes.
  • Easier to achieve uniform appearance, especially with colored renders.
  • Rough texture reduces rainwater penetration risk by distributing flow.
  • More dirt lodgement but discoloration is more even and less noticeable.

• Suitability Table Summary (Table I):

Recommended Mix Proportions (Clause 6.11)

• Typical mortar mix for rendering:
  1 part cement : 4 to 6 parts sand (by volume) depending on exposure and backing.

Functions of Different Coats & Thickness (Clause 6.13)

IS 2402: Preliminary Work - Key Points & Specifications

1. Preparatory Information (Clause 3.1 & 3.2)

Before rendering, provide detailed information to ensure proper material selection and application:

• Surface type: Brick, stone, concrete, etc.
• Rendered area and finish type
• Background nature:
  • Presence of soluble sulphates
  • Age of background (to assess drying time)
• Atmospheric conditions: Dust, acidic fumes, rain, wind exposure
• Drawings: Details at junctions (doors, windows), cornices, arrises, returns
• Decorative finish details over rendering
• Drawings and instructions for preparatory work must be provided.

2. Preliminary Work (Clause 7)

• Scaffolding: Must be safe and suitable for the work.
• Cleanliness: Background surfaces must be clean, free from dust, loose particles, oil, or other contaminants.
• Protection: Adjacent work and surfaces must be protected from damage or staining during rendering.

Summary Table: Preliminary Work Checklist

This ensures durable, high-quality rendering per IS 2402 standards.

IS 2402 - Application of Rendered Finishes: Key Specifications & Table

1. Suitability of Rendered Finishes (Clause 6.2 & Table I)

2. Important Notes (Clause 3.1 & 6.2.2)

• Background preparation depends on type (brick, stone, concrete), age, and soluble sulphates.
• Scraped/textured finishes reduce cracking and improve rainwater runoff, but may collect more dirt.
• Smooth finishes are aesthetically pleasing but more vulnerable to defects.
• Environmental factors like dust, acidic fumes, rain, and wind must be considered.

Summary Table: Crack Resistance & Dirt Lodgement

IS 2402 - Key Points on Curing of Rendered Finishes

Clause 9.1: Curing Requirements

• Duration: Keep each coat damp continuously for at least 2 days.
• Start: Begin moistening as soon as plaster hardens enough to avoid damage.
• Method: Use a fine fog-spray; avoid soaking.
• Precautions: Prevent excessive evaporation (sun/wind) by hanging wet mattings or gunny bags on the plaster surface.

Recommended Mix Proportions for Rendering (Clause 6.11, Table III)

Important Notes:

• Successive coats must not be richer in cement than the previous coat.
• Richer cement mixes preferred in winter.
• Use waterproofing admixtures for colored cement renderings.
• Avoid soaking; water should be absorbed readily.

Summary Diagram of Curing Process

flowchart TD
    A[Plaster Hardened] --> B[Start Moistening]
    B --> C[Apply Fine Fog-Spray]
    C --> D[Keep Surface Damp for 2 Days]
    D --> E{Is Weather Hot/Dry?}
    E -- Yes --> F[Hang Wet Mattings/Gunny Bags]
    E -- No --> G[Continue Normal Curing]
    F --> G
    G --> H[Achieve Maximum Strength & Density]

This ensures **maximum strength, durability

IS 2402: Cracks and Their Treatment – Key Points

1. Resistance to Cracking (Clause 6.6)

• Design and detailing should minimize shrinkage and thermal stresses.
• Use appropriate mix proportions and curing methods.
• Control joints and reinforcement help reduce crack widths.

2. Repairs to Cracks (Clause 10.2)

a) Cracks in Rendered Finishes Only (Clause 10.2.2)

• Cracks limited to surface rendering without background penetration require simple surface treatment (under preparation in the code).

b) Cracks Penetrating Rendering & Background (Clause 10.2.3)

• Ascertain and rectify the cause before repair.
• Restore the background fully.
• If full repair isn't possible:
  • Cut back rendering 15 cm on both sides of the crack.
  • Fix light expanded-metal mesh to the background.
  • Embed mesh in the undercoat of rendering.
• This reduces crack severity but may not prevent recurrence.
• For cracks at junctions of dissimilar materials, refer to Clause 6.6.5 (special detailing for mixed backgrounds).

Summary Table for Crack Treatment

Visual: Crack Repair Process

flowchart TD
    A[Crack Detected] --> B{Crack Type?}
    B -->|Rendering only| C[Surface Treatment]
    B -->|Penetrates background| D[Identify & Repair Cause]
    D --> E{Can background be fully repaired?}
    E -->|Yes| F[Restore background fully]
    E -->|No| G[Cut back 15 cm rendering]
    G --> H[Fix light expanded-metal mesh]
    H --> I[Embed mesh in undercoat]

Use light expanded-metal mesh and proper restoration to ensure durable repairs per IS 2402.

IS 2402: Repair of Damaged Areas – Key Points

• Clause 10.2.4 (Restoring Rendering):

  • Cut out damaged/cracked areas neatly.
  • Repair to match the background nature and finish type (as for new work).
  • Since exact matching is difficult, apply a uniform cement paint or decorative finish over the entire repaired surface for aesthetic consistency.

• Clause 11.3 (Mechanical Damage Repair):

  • Follow the same principles as crack repairs (Clause 10.2).
  • Ensure proper surface preparation and compatible materials.

• General Practice:

  • Remove loose or deteriorated material.
  • Use suitable repair mortar matching original in strength and texture.
  • Cure repaired areas adequately to prevent shrinkage cracks.

Typical Repair Mortar Mix (IS 2402 Reference)

Summary Diagram: Repair Process Flow

flowchart TD
    A[Identify Damage] --> B[Cut Out Damaged Area]
    B --> C[Clean & Prepare Surface]
    C --> D[Apply Repair Mortar]
    D --> E[Cure Properly]
    E --> F[Apply Finishing Coat]

Note: IS 2402 emphasizes matching repair materials and finishes to existing work for durability and appearance.

IS 2402: Maintenance and Protective Treatments - Key Points

1. Curing & Protection (Clause 9.2)

• After final finishing, keep surface wet for 7 days.
• Protect from temperature extremes and weather during curing.

2. Paint Treatments (Clause 11.5.3)

• Regular paint application prevents rain penetration.
• Follow IS 2395 for painting calcareous surfaces.

3. Water Penetration Resistance (Clause 6.4.1 & Table II)

• Water penetrates via pores/cracks; depends on permeability and suction.
• Backing material affects adhesion and protection needs:

4. Rendering Coats

• Two coats recommended on porous or weak backing.
• First coat: relatively impervious mix to reduce water ingress.
• Thickness and mix proportions as per Clause 6.11 (refer IS 2402 for detailed mix ratios).

flowchart TD
    A[Final Finishing Treatment] --> B[Keep Surface Wet for 7 Days]
    B --> C[Protect from Extreme Weather]
    C --> D[Apply Paint Treatments Regularly]
    D --> E[Prevent Rain Penetration]
    E --> F[Rendering Based on Backing Material]
    F --> G{Backing Material Type}
    G -->|

IS 2402: Colour and Decorative Finishes - Key Points

1. Types of Finishes & Suitability (Table I, Clause 6.2.2)

2. Important Notes

• Scraped/Textured finishes reduce cracking and crazing, offer uniform appearance, and better rainwater flow reducing penetration.
• Smooth finishes are more prone to defects.
• Colour choice should consider atmospheric pollution and sooty deposits (Clause 6.14.5).
• White/light colours need more maintenance in polluted/industrial environments.

3. Summary Diagram (Suitability Overview)

graph TD
    A[Finish Types] --> B[Pebble-dash/Dry-dash]
    A --> C[Roughcast]
    A --> D[Scraped finishes]
    A --> E[Textured finishes]
    A --> F[Smooth (Floated)]
    A --> G[Machine applied]
    A --> H[White/Light Colours]

    B --> I[Heavy rain & wind ✓]
    B --> J[Weak bricks ✗]
    D --> K[Less cracking ✓]

IS 2402 Key Specifications & Tables: Appendices & References

Appendix A (Clause 6.5.2.3 & Table III)

Measures to Overcome Effects of Soluble Sulphates on Renderings:

• A-1: Use either A-2 or A-3 methods.
• A-2: Provide a separate support for rendering by:
  • Battening out and applying metal lathing or subsidiary background.
• A-3: Use sulphate-resistant cement:
  • Sulphate-resisting Portland cement.
  • For severe conditions: High alumina cement or blast furnace slag cement.

Table II: Backgrounds for Renderings (Clause 6.3.2)

Additional Notes:

• Resistance to Water Penetration (6.4.1): Depends on permeability, suction, and water quantity.
• Recommended Mix Proportions: Refer Clause 6.11 for detailed mix ratios.
• Number & Thickness of Coats: Refer Clause 6.12 & 6.13 for recommended coats and thickness.

flowchart TD
    A[Background Material] --> B[Assess Strength & Porosity]
    B --> C{Is Porosity High?}
    C -- Yes --> D[Use Cement-Sand Mix 1:1]