Glossary of terms relating to gypsum
1976 Edition

Overview of IS 2469 Scope and Key Terms

• Scope (Clause 1.1): Establishes terminology associated with gypsum and its products employed in plaster, stucco, mortar, concrete, and gypsum boards.

• Principal Definitions:

  • Calcined Gypsum: Gypsum partially dehydrated, approximately CaSO4·½H2O.
  • Gypsum Board: Noncombustible sheet with gypsum core and paper facings.
  • Base Coat: Initial plaster layer composed of scratch and brown coats.
  • Finish Coat: Final plaster application layer.
  • Retarder/Accelerator: Chemicals that respectively delay or accelerate setting.
  • Normal Consistency: Milliliters of water per 100 grams of gypsum for specified flow.
  • Setting Time: Duration for gypsum plaster to harden after mixing.

• Gypsum Product Types:

  • Bond plaster, browning plaster, gauging plaster, metal lathing plaster, ready-mixed plaster, veneer plaster — each with distinct formulations and uses.

• Material Properties:

  • Standardized definitions for plasticity, consistency, setting time, and adhesion.

Normal Consistency Formula:

[ \text{Normal Consistency} = \frac{\text{Water volume (ml)}}{100 \text{ g gypsum}} ]

Diagram of Gypsum Plaster Layers:

graph TD
    A[Substrate] --> B[Base Coat (Scratch + Brown)]
    B --> C[Finish Coat]
    C --> D[Decorative Finish]

For comprehensive mix ratios, setting durations, and mechanical characteristics, consult the full IS 2469 documentation.

Core Terminology from IS 2469 Pertaining to Gypsum Materials

• Calcined Gypsum: Gypsum dehydrated by heat, formula approx. CaSO4·½H2O (hemihydrate).
• Hemihydrate: Intermediate gypsum dehydration phase, CaSO4·½H2O.
• Gypsum Board: Fire-resistant sheet with gypsum core and paper covering.
• Base Coat: First plaster layer, including scratch and brown coats.
• Brown Coat: Second layer in three-coat gypsum plaster systems.
• Finish Coat: Topmost plaster layer.
• Accelerator: Substance that speeds up plaster setting.
• Retarder: Substance that slows plaster setting.
• Consistency: Property relating to flow behavior of plaster.
• Normal Consistency: Water volume per 100 g plaster for specified fluidity.
• Plaster of Paris: Hemihydrate gypsum with no retarders added.
• Joint Reinforcement Tape/Metal: Materials for strengthening gypsum board joints.
• Gypsum Concrete: Mixture of aggregate and calcined gypsum binder that hardens.
• Gypsum Lath Varieties: Plain, perforated, insulating (aluminum foil backed), Type-X (fire-resistant).

Normal Consistency Equation:

[ \text{Normal Consistency} = \frac{\text{Water volume (ml)}}{100 \text{ g gypsum}} ]

Gypsum Product Classification Table

flowchart LR
    Gypsum -->|Calcination| Hemihydrate
    Hemihydrate -->|Water Addition| Plaster of Paris

Classification of Gypsum Plasters According to IS 2469

IS 2469 outlines several types of gypsum plaster distinguished by composition and intended application:

Key Parameters:

• Consistency: Water content per 100g plaster to achieve desired flow.
• Setting Time: Duration until plaster hardens post-mixing.
• Additives: Use of retarders and accelerators to adjust setting times.

Common Mix Ratios (by weight):

IS 2469 Definitions and Specifications for Gypsum Boards and Laths

Types of Gypsum Boards and Laths:

• Gypsum Board: Noncombustible panel with gypsum core and paper facings.
• Gypsum Lath Variants:
  • Plain: Solid sheet without perforations.
  • Perforated: Includes holes to improve plaster adhesion.
  • Insulating: Backed with aluminum foil for thermal insulation.
  • Type-X: Manufactured to provide fire resistance.

Important Terms:

• Base Coat: Initial plaster layer (scratch + brown coats).
• Finish Coat: Final decorative plaster layer.
• Core: Gypsum material inside paper facing.
• Joint Reinforcement Tape/Metal: Materials to strengthen gypsum board joints.

Material Types:

• Calcined Gypsum: Partially dehydrated gypsum (CaSO4·½H2O).
• Hemihydrate: Gypsum form used for plastering.
• Retarder/Accelerator: Additives to control setting time.

Application Layers Diagram:

flowchart TD
    A[Gypsum Lath/Base] --> B[Base Coat (Scratch + Brown)]
    B --> C[Finish Coat]

Consistency and Setting:

• Normal Consistency: Amount of water (ml) per 100g plaster for proper workability.
• Setting Time: Duration until plaster reaches required hardness.

Common Gypsum Product Types:

Refer to IS 2469 full text or complementary standards for detailed specifications.

Although IS 2469 mainly provides terminology, it references key additives used with gypsum products.

Overview of Additives and Modifiers:

• Accelerators: Chemicals that reduce setting time (e.g., calcium chloride).
• Retarders: Agents that prolong setting time (e.g., borax, glue).
• Binders: Fibrous components that enhance cohesiveness when plastic.
• Retarded Hemihydrate: Hemihydrate gypsum with added retarder.
• Keene’s Cement: Contains alum or aluminium sulphate as accelerators.
• Parian Cement: Contains borax as a retarder.
• Metal Lathing Plaster: Retarded hemihydrate plaster with free lime.

Practical Notes:

• Accelerators are useful in cold climates or to expedite construction.
• Retarders help extend working time in hot conditions or complex tasks.
• Binders improve mechanical integrity and reduce cracking.

Typical Dosages (by weight % of gypsum):

Approximate Formula for Adjusted Setting Time:

[ t_s = t_0 \times \frac{1}{1 + k_a A - k_r R} ]

where:

• (t_s) = adjusted setting time
• (t_0) = base setting time without additives
• (A) = accelerator dosage
• (R) = retarder dosage
• (k_a, k_r) = empirical constants

For detailed additive effects, consult IS 2542 or ASTM C11 standards.

Terminology for Gypsum Plaster Coats as per IS 2469

Gypsum plastering generally involves multiple layers, each serving a defined purpose:

Main Layers:

• Base Coat: The initial plaster layer, often subdivided into:
  • Scratch Coat: First application, scratched to provide mechanical key.
  • Brown Coat: Second application, smooths and levels surface.
• Finish Coat: Thin final layer providing smoothness and aesthetic finish.

Plaster Types for Each Layer:

Specifications:

• Base coat thickness typically ranges from 6 to 12 mm (combined scratch and brown coats).
• Finish coat thickness usually between 1.5 to 3 mm.
• Consistency and setting times are controlled via water content and additives.

Additional Notes:

• Perforated gypsum lath is recommended for mechanical bonding of base coats.
• Retarders and accelerators adjust working and setting times respectively.
• Proper layering ensures durability, crack resistance, and surface smoothness.

flowchart TD
    A[Substrate] --> B[Scratch Coat (Base)]
    B --> C[Brown Coat (Base)]
    C --> D[Finish Coat]

This system assures optimal adhesion and finish quality.

Key Definitions and Specifications for Gypsum Concrete per IS 2469

• Gypsum Concrete: Combination of aggregate, calcined gypsum binder, and water that sets into a solid mass.
• Calcined Gypsum: Gypsum partially dehydrated to CaSO4·½H2O.
• Gypsum Neat Plaster: Calcined gypsum plaster without aggregates, used as a base coat.
• Gauging Plaster: Calcined gypsum mixed with lime for finish coats.
• Additives: Retarders and accelerators to manage setting times.
• Consistency: Water volume per 100 g gypsum to achieve desired flow.
• Setting Time: Time required for plaster to harden after mixing.

Typical Mix Ratios (by volume):

Remarks:

• Aggregate mainly serves as filler rather than binder.
• Gypsum boards feature paper facings; types include plain, perforated, and fire-resistant Type-X.
• Brown coat is the secondary plaster layer; base coat is the primary.
• Joint reinforcement materials are applied for gypsum board seams.

flowchart LR
    A[Calcined Gypsum] --> B[Add Water]
    B --> C[Add Aggregate]
    C --> D[Gypsum Concrete]
    B --> E[Add Lime]
    E --> F[Gauging Plaster]
    B --> G[Neat Plaster (No Aggregate)]

For detailed mix designs, refer to IS 2469 full documentation and ASTM C11.

IS 2469 Overview of Joint Reinforcement Materials

Joint Reinforcement Types:

• Joint Reinforcing Tape: Made from paper, metal, fabric, or fiberglass mesh, used with compounds to strengthen gypsum board joints.
• Joint Reinforcing Metal: Includes expanded metal strips, woven or welded wire mesh for corners and plaster-lath reinforcement.

Specifications and Application:

• Reinforcement must provide mechanical interlock and resistance to cracking.
• Materials must be compatible with gypsum plaster, resisting corrosion and degradation.
• Metal mesh should exhibit sufficient tensile strength and corrosion resistance.

Typical Properties:

Best Practices:

• Fully embed reinforcement within joint compound.
• Utilize metal reinforcement at corners and high-stress zones.
• Overlap joints by at least 50 mm for continuous reinforcement.

flowchart LR
    A[Gypsum Board Joints] --> B[Apply Joint Compound]
    B --> C[Embed Reinforcing Tape or Mesh]
    C --> D[Finish Coat Application]
    D --> E[Surface Sanding and Finishing]

Summary: Proper use of reinforcement materials embedded in plaster ensures durability and crack resistance in gypsum board construction.

IS 2469 Definitions Relating to Physical Properties and Testing of Gypsum Products

The standard provides terminology referencing ASTM C-11-70 for gypsum characteristics.

Key Terms:

• Calcined Gypsum: Partially dehydrated gypsum with formula CaSO4·½H2O.
• Hemihydrate: Calcium sulfate hemihydrate phase.
• Setting Time: Time interval for gypsum plaster to harden after mixing.
• Consistency: Flow property measured as milliliters of water per 100 g gypsum.
• Retarder/Accelerator: Additives that respectively slow or speed setting.
• Gypsum Board Varieties: Plain, perforated, fire-resistant Type-X, sheathing, backing, etc.
• Plaster Layers: Scratch coat (base), brown coat (second), finish coat (final).

Standard Testing Methods:

• Setting Time: Determined using Vicat needle or Gillmore apparatus.
• Consistency: Water volume required for normal flow.
• Compressive Strength: Tested on hardened plaster specimens.

Typical Normal Consistency Values:

Summary Table of Gypsum Product Types:

flowchart LR
    A[Gypsum] --> B[Calcined Gypsum (CaSO4·½H2O)]
    B --> C[Neat Plaster]
    B --> D[Gauging Plaster + Lime]

While IS 2469 mainly defines gypsum product terminology, it indirectly addresses fire resistance and special gypsum product types.

Fire-Resistant Gypsum Products:

• Type-X Gypsum Board: Special gypsum lath containing additives like glass fibers to enhance fire resistance.
• Fire performance depends on:
  • Gypsum layer thickness (commonly 12.5 mm or more)
  • Number of layers installed
  • Use of fire-retardant additives such as alum or borax
• Typical fire ratings range from 1 to 4 hours based on assembly design.

Specialized Gypsum Materials:

• Gypsum Fibre Concrete: Mixture of gypsum and wood fibers to increase toughness.
• Gypsum Partition Blocks: Non-load bearing blocks offering fire protection.
• Additives: Accelerators and retarders like alum and borax to control setting.
• Insulating Gypsum Lath: Backed with aluminum foil for improved thermal insulation.

Product Specifications:

Setting Time Modifiers:

• Accelerators (e.g., calcium chloride) speed up setting.
• Retarders (e.g., borax) slow down setting.

flowchart TD
    A[Gypsum Products] --> B[Standard Gypsum Board]
    A --> C[Type-X Fire-Resistant Board]
    A --> D[Gypsum Fibre Concrete]
    A --> E[Partition Blocks]
    C --> F[Fire Resistance: 1-4 Hours]
    D --> G[Enhanced Mechanical Toughness]
    E --> H[Non-Load Bearing Fire Protection]

Summary: IS 2469 establishes gypsum product terminology; fire resistance attributes depend on product type, thickness, and additive content. Specialized gypsum products serve diverse structural and fire safety roles.