Glossary of terms relating to building finishes
1983 Edition

Overview of IS 10403: Scope and Objectives

• Purpose: This document standardizes terminology related to building finishes, aligning Indian construction practices with international norms.
• Highlights: Defines key terms such as Floating Coat (Section 2.56.2) used in multi-layer plastering systems.
• Coverage: Encompasses materials, application procedures, and quality assurance for finishing surfaces.
• Global Coordination: Ensures compatibility with worldwide standards while addressing India-specific construction conditions.

Illustrative Definition

Contact Information

• Central Office: Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002
• Central Testing Laboratory: Sahibabad Industrial Area, Plot No. 20/9, Site IV
• Various regional and branch offices across India provide technical assistance and facilitate standards procurement.

Note: IS 10403 focuses on terminologies; for structural design data, consult related IS standards such as IS 456 or IS 875.

Detailed Glossary of Building Finishes in IS 10403

This standard provides precise definitions rather than computational formulas or tables. It clarifies terms crucial for consistent interpretation in construction and finishing operations.

Commonly Defined Terms Include:

• Plaster: A mixture applied to wall or ceiling surfaces to create a smooth or textured finish.
• Paint: Colored liquid coatings serving protective and decorative purposes.
• Varnish: Transparent finish applied primarily on wood for protection.
• Flooring: The final surface layer on floors, including tiles, wood, and stone.
• Wall Finishing: Treatments applied to walls such as plaster, paint, or wallpaper.
• Roofing: Materials and finishes applied to roof surfaces, including tiles and sheets.

Importance:

• Promotes consistent use of terminology in contract documents and specifications.
• Eliminates confusion in material selection and workmanship standards.

Since this is a glossary, no technical tables or formulas are included. For detailed technical specifications, refer to IS codes like IS 383 for aggregates, IS 1542 for paints, and IS 1237 for floor tiles.

flowchart LR
    A[Building Finishes] --> B[Flooring]
    A --> C[Wall Treatments]
    A --> D[Roofing]
    B --> E[Tiles]
    B --> F[Wood]
    C --> G[Plaster]
    C --> H[Paint]
    D --> I[Tiles]
    D --> J[Sheets]

IS 10403: Description and Specifications of Acoustic Plaster

• Definition (Clause 2.1): Acoustic plaster is formulated to improve sound absorption and reduce reverberation on surfaces.

• Material Composition:

  • Primarily gypsum-based (Clause 2.33) or alternative materials.
  • Applied in a plastic form and hardens after application (Clause 2.39).
  • Commonly supplied as a thin plaster suitable for spray application (Clause 2.55).

Typical Characteristics

Sound Absorption Coefficient Formula

[ \alpha = \frac{I_{absorbed}}{I_{incident}} = 1 - \frac{I_{reflected}}{I_{incident}} ]

• (I_{incident}): Intensity of incoming sound
• (I_{reflected}): Intensity of reflected sound
• (I_{absorbed}): Intensity of absorbed sound

Application Guidelines:

• Ensure substrate is clean and stable.
• Thicker layers improve absorption at lower frequencies.
• Surface porosity and texture significantly influence performance.

flowchart LR
    A[Prepare Substrate] --> B[Apply Acoustic Plaster]
    B --> C[Allow Drying and Hardening]
    C --> D[Achieve Enhanced Sound Absorption]

Summary: Acoustic plaster as per IS 10403 is a specialized gypsum-based plaster enhancing acoustic properties when applied thinly, with performance depending on thickness and surface characteristics.

Backing Coat (Undercoat) as Defined in IS 10403

• Definition (Clauses 2.6 & 2.56): A plaster layer other than the final coating, serving primarily to prepare a proper surface for subsequent coats.

• Variants of Backing Coat:

  • Rendering Coat (First Coat) [Clause 2.56.1]: The initial layer applied directly on the substrate.
  • Floating Coat (Second Coat) [Clause 2.56.2]: In three-layer plastering, this coat smooths and levels the surface before the finishing coat.

Specifications Summary

Typical Mix Ratios

• Rendering Coat: Cement to sand ratio ranges from 1:4 to 1:6
• Floating Coat: Cement to sand ratio ranges from 1:3 to 1:5

Typical Thickness

• Rendering Coat: 6 to 12 mm
• Floating Coat: 6 to 10 mm

Application Process Diagram

flowchart LR
    A[Building Surface] --> B[Rendering Coat]
    B --> C[Floating Coat (if applicable)]
    C --> D[Final Finishing Coat]

Note: For detailed mix designs and application procedures, consult the full IS 10403 standard and related plastering codes.

Bell Coat Definition and Application (IS 10403)

Definition (Clause 2.8):

• The bell coat is the shaping of the lower edge of an external plaster or rendering designed to effectively divert rainwater away from the wall surface, preventing water damage.

Specifications

• Function: To form a drip edge by curving or beveling the bottom edge of the external plaster.
• Design Considerations: Ensures water drips clear of the wall face.
• Thickness: Generally matches the finishing coat thickness but shaped to create the drip profile.

Related Coat Types

Practical Notes

• Bell coat is typically formed by rounding or chamfering the plaster edge.
• Common projection or radius: 5 to 10 mm beyond the wall face.
• Helps enhance durability by minimizing water retention on external surfaces.

flowchart LR
    A[Wall Surface] --> B[Rendering Coat]
    B --> C[Floating Coat]
    C --> D[Bell Coat (Drip Edge)]
    D --> E[Water Diverts Away from Wall]

Summary: The bell coat is a critical detail in external plastering that promotes rainwater runoff and protects wall surfaces from moisture damage.

Blistering in Plastering as per IS 10403: Essential Details

• Definition (Clause 2.10):
  Blistering refers to the appearance of raised bubbles or swellings on the surface of finished plaster.

• Causes:
  Typically results from trapped air, excess water in the mix, or improper curing leading to surface defects.

• Associated Defects:

  • Popping (2.42): Conical voids caused by expansion of reactive particles.
  • Peeling (2.38): Detachment of large plaster areas from the substrate.
  • Bleeding (2.9): Separation of water from the plaster mix before setting.

Prevention Techniques

Water-Cement Ratio Guideline

[ w/c \approx 0.5 \text{ (maximum for quality plastering)} ]

Blistering Formation Flow

flowchart LR
    A[Mixing] --> B[Entrapped Air]
    B --> C[Surface Drying]
    C --> D[Expansion of Air Pockets]
    D --> E[Blister Formation]

Note: IS 10403 defines blistering but does not include specific formulas; adherence to good plastering protocols is essential to avoid this defect.

Cracking in Plaster According to IS 10403: Key Points

• Definition (Clause 2.15):
  Cracks are fissures on plaster surfaces not resulting from structural failures. Cracks adjacent to structural cracks are considered structural only if they coincide exactly.

• Related Surface Imperfections:

  • Crazing (2.16): Fine, hairline cracks forming a pattern resembling a map.
  • Combing (2.14): Parallel scratch marks made on intermediate coats to enhance bonding.
  • Hacking (2.34): Roughening of the substrate to provide a mechanical key for plaster adhesion.

Managing and Preventing Cracks

• Maximum Allowable Crack Width: Typically limited to 0.3 mm to keep cracks from being conspicuous.

• Crack Width Formula:

[ w = \varepsilon \times L ]

where (w) = crack width, (\varepsilon) = strain differential, and (L) = crack length.

• Preventive Measures:
  • Proper curing
  • Adequate substrate preparation (hacking)
  • Use of control joints
  • Correct mortar mix proportions

Summary of Surface Treatments

flowchart TD
    A[Substrate Preparation] --> B[Hacking]
    B --> C[Intermediate Coat]
    C --> D[Combing]
    D --> E[Final Coat]
    E --> F{Crack Presence?}
    F -- No --> G[Acceptable Finish]
    F -- Yes --> H[Assess Cause]
    H -- Structural --> I[Structural Repairs]
    H -- Non-Structural --> J[Re-plastering]

Crazing Phenomenon in Plaster as per IS 10403: Overview and Control

• Definition (Clause 2.16):
  Crazing describes numerous fine, hairline cracks on plaster surfaces, often creating irregular map-like patterns.

• Difference from Other Defects:

  • Unlike cracking (Clause 2.15) which involves wider fissures.
  • Different from blistering (Clause 2.10) which shows surface swellings.

• Common Causes:

  • Rapid drying post-application
  • Excess water in plaster mix
  • Insufficient curing
  • Use of non-uniform or inappropriate materials

• Preventive Measures:

  • Maintain water-cement ratio between 0.5 and 0.6
  • Ensure adequate curing for a minimum of seven days
  • Use appropriate cement to sand ratios, such as 1:4 by volume
  • Avoid excessive surface troweling

• Note: IS 10403 does not specify formulas for crazing; adherence to standard plaster mix and curing protocols is recommended.

Causes and Remedies Table

flowchart LR
    A[Apply Plaster] --> B{Water Content}
    B -- Excess --> C[Crazing Develops]
    B -- Optimal --> D[Good Finish]
    A --> E{Curing}
    E -- Insufficient --> C
    E -- Adequate --> D

Reference: For detailed mix design and curing, consult IS 1661 related to cement plaster.

Terminology and Application of Dash Finishes in IS 10403

Definitions (Clause 2.17 series)

• Dry Dash (2.17.1): Coarse aggregate is thrown onto a freshly applied, soft final mortar coat and left exposed.
• Wet Dash (2.17.2): Coarse aggregate is mixed into the wet final coat mortar and applied to create a rough textured surface.
• Dashed Finish (2.17): A general term for rough-textured external rendering using either dry or wet dash methods.
• Final Coat (2.23): The last continuous mortar layer; for dry dash, the base layer on which aggregate is applied; for wet dash, the mortar containing aggregate.

Key Parameters

• Aggregate Size: Usually ranges from 3 to 6 mm for finer finishes, up to 10 mm for coarser textures.
• Aggregate Content in Wet Dash: Typically 20-30% by volume within the final coat.
• Mortar Mix: Cement to sand ratios commonly between 1:3 and 1:5, adjusted based on exposure and finish quality.

Application Considerations

• Dry dash requires prompt throwing of aggregate onto still-soft mortar.
• Wet dash involves mixing aggregate uniformly into the mortar before application.

Summary Table

flowchart TD
    A[Final Mortar Coat] -->|Fresh & Soft| B[Dry Dash: Throw Aggregate]
    A -->|Aggregate Mixed| C[Wet Dash: Apply Mixture]
    B --> D[Coarse Aggregate Surface]
    C --> D

This summary corresponds with IS 10403 provisions and typical field practices for dash finish applications.

Specifications and Role of the Final Coat in IS 10403

• Definition (Clause 2.23):
  The final coat is the last continuous rendering layer applied over plastered surfaces.

  • For dry finishes, it serves as the base to which dry dash aggregate is applied while still soft.
  • For roughcast or machine finishes, it constitutes the ultimate finishing layer.

• Related Coats:

  • Rendering Coat (First Coat): Initial plaster layer directly on the substrate (Clause 2.56.1).
  • Floating Coat (Second Coat): Intermediate leveling coat before the final finish (Clause 2.56.2).

Application Details

Typical Layering Sequence

graph LR
  A[Substrate] --> B[Rendering Coat (1st)]
  B --> C[Floating Coat (2nd)]
  C --> D[Final Coat (3rd)]

Notes

• Final coat quality significantly impacts durability and appearance.
• Adhere to IS 1661 for mortar mix ratios and curing methods.
• Uniform thickness is critical to prevent cracking and peeling.

For detailed mix designs and curing methods, see IS 1661 and IS 2250.

IS 10403 Overview of Finishing Methods

1. Scraped Finish (Clause 2.27.2)

• Procedure:
  • Apply the final rendering coat.
  • Level the surface evenly.
  • Allow the coat to stiffen for several hours.
  • Scrape the surface layer with an appropriate tool to reveal a consistent texture.
• Purpose:
  • Provides a smooth, matte finish with subtle roughness enhancing visual appeal and paint adhesion.

2. Sponge Plaster Finish (Clause 2.27.6)

• Procedure:
  • Apply the final plaster coat.
  • While still fresh, gently dab the surface with a damp sponge.
  • Produces a textured, mottled pattern with a soft appearance.
• Purpose:
  • Decorative finish often used to reduce glare and conceal minor surface flaws.

Additional Notes

• Both finishes fall under textured finishes (Clause 2.27.5), involving treatment of the fresh final coat.
• No specific thickness requirements; typical plaster thickness ranges from 12 to 20 mm depending on substrate and finish.
• Tools required: Scraper for scraped finish; natural or synthetic sponges for sponge finish.

flowchart LR
    A[Apply Final Coat] --> B{Choose Finish Type}
    B --> C[Scraped Finish]
    B --> D[Sponge Plaster Finish]
    C --> E[Level, Stiffen, Scrape Surface]
    D --> F[Apply Wet Sponge Dab]
    E --> G[Matte Textured Surface]
    F --> H[Soft Patterned Texture]

Consult IS 10403 and plastering manuals for detailed application guidance.

IS 10403 Explanation of Flaking in Plastering

Definition (Clause 2.28)

• Flaking: The detachment and scaling off of patches of plaster surface caused by a loss of adhesion to the underlying coat.

Primary Causes

• Insufficient surface preparation such as inadequate hacking or cleaning.
• Use of incompatible plaster layers.
• Moisture penetration or improper curing practices.

Preventive Measures

• Perform hacking (Clause 2.34) to roughen the substrate for mechanical bonding.
• Maintain proper curing regimes and control moisture exposure.
• Employ compatible plaster mixes and bonding agents.

Related Terms

Typical Hacking Specification

Adhesion Strength Concept

[ \text{Adhesion Strength} = \frac{\text{Force required to detach plaster}}{\text{Plastered Surface Area}} ]

Recommended adhesion strength to prevent flaking: ≥ 0.15 N/mm².

flowchart LR
    A[Prepare Substrate] --> B[Hacking]
    B --> C[Apply Initial Coat]
    C --> D[Apply Subsequent Coat]
    D --> E{Adequate Adhesion?}
    E -- Yes --> F[Durable Finish]
    E -- No --> G[Flaking/Peeling Occurs]

Summary: Flaking is caused by poor adhesion; ensuring proper hacking, compatible materials, and curing per IS 10403 mitigates this issue.

IS 10403 - Definition and Guidelines for Gauging in Plastering

Definition (Clause 2.30):

• Gauging is the process of blending different plaster constituents.
• It also refers to the addition of cement to lime-sand mixes or lime to cement-sand mixes.
• A single plaster application is often referred to as a gauging.

Typical Constituent Ratios

Important Considerations

• Water: Added to achieve workable consistency; excessive water leads to shrinkage.
• Mixing: Uniform blending is crucial for consistent strength and finish.
• Curing: Proper curing after gauging ensures hardness and longevity.

Approximate Strength Formula for Gauged Lime Plaster

[ \text{Compressive Strength} \approx \text{Strength of Lime} \times \frac{\text{Cement}}{\text{Lime} + \text{Cement}} \times \text{Sand Factor} ]

(Sand factor depends on particle grading and quality)

flowchart LR
    A[Constituents: Lime, Cement, Sand] --> B[Mixing: Gauging]
    B --> C[Plaster Application]
    C --> D[Curing Process]
    D --> E[Final Strength and Surface Finish]

Refer to IS 1661 and IS 2250 for detailed mix proportions and standards.

IS 10403 - Overview of Gypsum Plaster

• Gypsum Plaster (Clause 2.33): Made primarily from calcium sulphate, used for smooth finishing applications.

• Semi-hydrate Gypsum Plaster (Clause 2.33.2): Partially calcined gypsum retaining some water content, providing moderate setting times.

• Pre-mixed Lightmass Gypsum Plaster (Clause 2.33.3): Gypsum plaster combined with lightweight aggregates to reduce density and improve thermal insulation.

Typical Properties

Mixing Ratio Formula

[ \text{Water} : \text{Gypsum} = 0.5 \text{ to } 0.6 \text{ by weight} ]

Application Guidelines

• Use clean water for mixing.
• Mix to a smooth, lump-free consistency.
• Apply within 30 minutes to avoid premature setting.

flowchart LR
    A[Raw Gypsum (CaSO₄·2H₂O)] --> B[Calcining]
    B --> C[Semi-hydrate Gypsum Plaster]
    B --> D[Anhydrous Gypsum]
    C --> E[Lightmass Gypsum Plaster with Lightweight Aggregates]

This summary is consistent with IS 10403 definitions and practical gypsum plaster usage.

IS 10403 - Overview of Pugging in Construction

• Definition (Clause 2.44): Pugging is the placement of coarse material above ceilings, between joists, to enhance sound insulation.
• Typically composed of coarse, inert materials such as crushed bricks, gravel, or similar substances.
• Its function is to reduce sound transmission by adding mass and damping effects.

Pugging Material Specifications

Related Terms

• Green Suction (2.31): Early suction of cement backing during setting for proper bonding.
• Plasticizer (2.41): Additives that enhance mix plasticity, often by entraining air.
• Spatterdash (2.53): Cement-sand slurry applied as a key coat on dense surfaces.
• Suction (2.54): Rate at which background surfaces absorb water, influencing plaster adhesion.

Pugging Placement Diagram

graph TD
  Ceiling -->|Joists| Joists
  Joists -->|Pugging Layer| Pugging[Coarse Material]
  Pugging -->|Soundproofing Effect| Soundproofing

Note: While IS 10403 does not specify explicit formulas for pugging, it emphasizes correct material selection and positioning for acoustic performance.

IS 10403 - Retempering Practices and Guidelines

• Definition (Clause 2.47): Retempering involves remixing plaster or rendering material that has begun to stiffen but has not yet set.

• Purpose: To restore workability without reducing strength or finish quality.

• Restrictions:

  • Only permitted before the final set (Clause 2.24), i.e., while the mix remains plastic.
  • Avoid retempering after final set to prevent strength loss and surface defects.
  • Use minimal additional water; excess water weakens plaster.

• Practical Recommendations:

  • Retemper within 30 to 60 minutes after initial mixing.
  • Do not add cement or lime during retempering.
  • Ensure uniform consistency after remixing.

Effects Summary

| Parameter | Before Final Set | After Final Set (Not Recommended) |\n|---------------------|--------------------------|-----------------------------------| | Workability | Restored | Lost | | Strength | Maintained if water addition is minimal | Reduced | | Surface Finish | Smooth | Disrupted or polished |

flowchart LR
    A[Mix Stiffening Begins] --> B{Time < Final Set?}
    B -- Yes --> C[Retemper: Remix with Minimal Water]
    B -- No --> D[No Retempering Allowed]
    C --> E[Apply Plaster or Rendering]
    D --> F[Discard or Replace Mix]

Note: IS 10403 stresses timing and controlled retempering to maintain quality of plaster or rendering.