Glossary of terms relating to gypsum

IS 2469: Scope & Key Specifications Summary

• Scope (Clause 1.1): Defines terms related to gypsum and gypsum products used in plaster, stucco, mortar, concrete, and boards.

• Key Definitions:

  • Calcined Gypsum: Partially dehydrated gypsum, approx. CaSO4·½H2O.
  • Gypsum Board: Noncombustible sheet with gypsum core and paper surfacing.
  • Base Coat: First plaster layer (scratch coat + brown coat).
  • Finish Coat: Final plaster layer.
  • Retarder/Accelerator: Substances to delay/hasten setting.
  • Normal Consistency: Water (ml) per 100 g gypsum for specified fluidity.
  • Setting Time: Time for gypsum plaster to harden after mixing.

• Types of Gypsum Products:

  • Bond Plaster, Browning Plaster, Gauging Plaster, Metal Lathing Plaster, Ready-Mixed Plaster, Veneer Plaster — each with specific uses and compositions.

• Material Properties:

  • Plasticity, consistency, setting time, and bonding definitions are standardized.

Typical Formula for Normal Consistency:

[ \text{Normal Consistency} = \frac{\text{Volume of water (ml)}}{100,g,\text{gypsum}} ]

Conceptual Diagram of Gypsum Plaster Layers:

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

For detailed mix ratios, setting times, and mechanical properties, refer to IS 2469 full text or relevant annexes.

Key Terms & Definitions from IS 2469: General Terms Related to Gypsum

• Calcined Gypsum: Partially dehydrated gypsum by heat; formula approx. CaSO₄·½H₂O (Hemihydrate).
• Hemihydrate: Intermediate phase in gypsum dehydration; formula CaSO₄·½H₂O.
• Gypsum Board: Noncombustible sheet with gypsum core and paper surfacing.
• Base Coat: First plaster layer (scratch coat + brown coat).
• Brown Coat: Second coat in three-coat gypsum plaster.
• Finish Coat: Final plaster layer over base coat.
• Accelerator: Substance that hastens setting of plaster/mortar.
• Retarder: Substance that delays setting.
• Consistency: Flow-force relation property of plaster.
• Normal Consistency: Water (ml) per 100g plaster for specified fluidity.
• Plaster of Paris: Hemihydrate gypsum without set retarders.
• Joint Reinforcing Tape/Metal: Materials to reinforce gypsum board joints.
• Gypsum Concrete: Aggregate + calcined gypsum binder, sets to solid mass.
• Gypsum Lath Types: Plain, Perforated, Insulating (with aluminum foil), Type-X (fire retardant).

Typical Formula for Normal Consistency:

[ \text{Normal Consistency} = \frac{\text{Volume of water (ml)}}{100 \text{ g of gypsum}} ]

Summary Table: Gypsum Product Types

flowchart LR
    Gypsum -->|Calcination| Hemihydrate
    Hemihydrate -->|Mix with water| Plaster of

Types and Forms of Gypsum Plaster (IS 2469 Key Points)

IS 2469 defines gypsum plasters with various forms and applications:

Key Specifications:

• Consistency: Water per 100g plaster to achieve specified flow.
• Setting Time: Time to reach specified hardness after mixing.
• Retarders/Accelerators: Used to control setting time.

Typical Mix Proportions (by weight):

IS 2469: Key Specifications & Definitions for Gypsum Boards and Laths

Gypsum Boards & Laths Types:

• Gypsum Board: Core of gypsum with paper surfacing; noncombustible sheets.
• Gypsum Lath:
  • Plain: Without perforations.
  • Perforated: With holes for mechanical keying.
  • Insulating: Back covered with aluminum foil.
  • Type-X: Fire retardant.

Important Terms:

• Base Coat: First plaster layer (scratch coat + brown coat).
• Finish Coat: Final plaster layer.
• Core: Gypsum inside the paper covering.
• Joint Reinforcing Tape/Metal: For reinforcing board joints.

Material Types:

• Calcined Gypsum: Partially dehydrated gypsum (CaSO4·½H2O).
• Hemihydrate: CaSO4·½H2O, used in plaster.
• Retarder/Accelerator: Modify setting time.

Typical Application Layers:

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

Consistency & Setting:

• Normal Consistency: ml water per 100g plaster for required fluidity.
• Setting Time: Time to reach hardness post-mixing.

Common Gypsum Products:

For detailed mix proportions, setting times, and mechanical properties, refer to IS 2469 full standard or related ASTM/BS standards.

IS 2469 primarily defines terms related to gypsum products but does not provide explicit formulas or tables for additives and modifiers.

Key Points on Additives and Modifiers (from IS 2469 definitions):

• Accelerator: Substance to hasten setting (e.g., calcium chloride).
• Retarder: Substance to delay setting (e.g., borax, glue).
• Binder: Fibrous material to increase cohesiveness in plastic state.
• Retarded Hemihydrate: Hemihydrate plaster with added retarder.
• Keene’s Cement: Contains alum/aluminium sulphate (accelerator).
• Parian Cement: Contains borax (retarder).
• Metal Lathing Plaster: Retarded hemihydrate plaster with free lime.

Practical Notes:

• Accelerators reduce setting time, useful in cold weather or rapid construction.
• Retarders extend working time, useful in hot climates or complex applications.
• Binders improve mechanical strength and reduce cracking.

Typical Additive Dosage (general practice):

Setting Time Adjustment Formula (approximate):

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

• (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 mix design and performance, consult IS 2542 (Gypsum Plaster) or ASTM C11 for additive effects.

flowchart LR
    Additives -->|Accelerator| Faster_Setting
    Additives -->|Retarder| Slower_Setting
    Additives -->|Binder| Increased_Cohesiveness
    Faster_Setting --> Construction_Speed
    Slower_Setting --> Workability
    Increased_Cohesiveness --> Strength_

IS 2469: Coats and Layers in Gypsum Plastering

Gypsum plastering typically involves multiple coats, each with specific functions:

Key Coats:

• Base Coat: First layer, often two sub-layers:
  • Scratch Coat: First application, scratched to provide mechanical key.
  • Brown Coat: Second application, smoothens surface.
• Finish Coat: Final thin layer for smoothness and decoration.

Types of Plasters for Coats:

Specifications:

• Base Coat Thickness: Usually 6-12 mm (2 coats combined).
• Finish Coat Thickness: Typically 1.5-3 mm.
• Consistency: Water per 100g plaster varies; normal consistency ensures workability.
• Setting Time: Controlled by retarders/accelerators.

Notes:

• Use perforated gypsum lath for mechanical keying of base coats.
• Retarders slow setting; accelerators speed it up.
• Proper layering ensures durability, crack resistance, and smooth finish.

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

This layering ensures good adhesion, strength, and surface finish as per IS 2469 definitions.

IS 2469 Key Specifications & Terms for Gypsum Concrete and Related Products

• Gypsum Concrete: Aggregate(s) + calcined gypsum binder + water → sets into a solid mass.
• Calcined Gypsum: CaSO4·½H2O (hemihydrate), formed by partial dehydration of gypsum.
• Gypsum Neat Plaster: Calcined gypsum plaster without aggregate, used for base coats.
• Gauging Plaster: Calcined gypsum plaster mixed with lime, used as finish coat.
• Retarder & Accelerator: Chemicals to control setting time (retarder slows, accelerator hastens).
• Consistency: Water volume per 100g gypsum for desired flow (normal consistency).
• Setting Time: Time for plaster to harden after mixing with water.

Typical Mix Proportions (by volume)

Important Notes:

• Aggregate acts as filler, not binder.
• Gypsum boards have paper surfacing; types include plain, perforated, and Type-X (fire-resistant).
• Brown coat = second plaster layer; base coat = first layer.
• Joint reinforcing tape/metal is used for gypsum board joints.

flowchart LR
    A[Calcined Gypsum] --> B[Mix with 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 design and setting times, refer to IS 2469 full text and related ASTM C-11.

IS 2469 - Joint Reinforcement Materials: Key Points

Types of Joint Reinforcement

• Joint Reinforcing Tape: Paper, metal, fabric, or glass mesh used with cementitious compounds to reinforce gypsum board joints.
• Joint Reinforcing Metal: Expanded metal strips, woven or welded wire mesh for reinforcing corners and plaster-lath areas.

Specifications & Usage

• Reinforcement materials must provide mechanical keying and crack resistance.
• Materials should be compatible with gypsum plaster and not cause corrosion or deterioration.
• Metal lath or mesh must have adequate tensile strength and corrosion resistance.

Typical Properties (per IS 2469 and related standards)

Application Tips

• Embed tape or mesh fully in the joint compound.
• Use metal reinforcement at corners and stress points.
• Ensure overlap of at least 50 mm at joints for continuous reinforcement.

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

Summary: Use appropriate joint reinforcement (tape or metal mesh) embedded in plaster to ensure durability and crack resistance in gypsum board assemblies per IS 2469.

IS 2469 - Physical Properties & Testing Terms for Gypsum

The code primarily defines key terms related to gypsum and its products, referencing ASTM C-11-70 for standard definitions.

Key Definitions:

• Calcined Gypsum: Partially dehydrated gypsum (CaSO4·½H2O).
• Hemihydrate: Calcium sulfate hemihydrate (CaSO4·½H2O), intermediate dehydration phase.
• Setting Time: Time for gypsum plaster to harden after mixing.
• Consistency: Flow property of gypsum mix; measured as ml of water per 100g gypsum.
• Retarder/Accelerator: Chemicals that slow down or speed up setting.
• Gypsum Board Types: Plain, Perforated, Type-X (fire-resistant), Sheathing, Backing, etc.
• Coats in Plastering: Scratch coat (base), brown coat (second), finish coat (final).

Typical Physical Property Testing:

• Setting Time: Measured by Vicat needle or Gillmore apparatus.
• Consistency: Water required for normal flow (ml/100g).
• Compressive Strength: Tested on set plaster cubes or cylinders.

Example: Normal Consistency

Summary Table of Gypsum Types:

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

IS 2469 primarily defines gypsum product terms but does not explicitly specify fire resistance formulas or special gypsum product specs.

For Fire Resistance & Special Gypsum Products (based on IS 2469 context + engineering practice):

Fire Resistance

• Type-X Gypsum Board: Special gypsum lath with additives (e.g., glass fibers) to improve fire resistance.
• Fire resistance depends on:
  • Thickness of gypsum layers (usually 12.5 mm or more)
  • Number of gypsum board layers
  • Use of fire-retardant additives (e.g., alum, borax)
• Typical fire rating: 1-4 hours depending on assembly.

Special Gypsum Products

• Gypsum Fibre Concrete: Gypsum + wood fibers for enhanced toughness.
• Gypsum Partition Blocks: Non-load bearing, fire-protective blocks.
• Accelerators/Retarders: Control setting time; alum or borax as additives.
• Insulating Gypsum Lath: Backed with aluminum foil for thermal insulation.

Important Specifications:

Setting Time Control:

• Accelerator: Hastens set (e.g., calcium chloride).
• Retarder: Delays set (e.g., borax).

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 hrs]
    D --> G[Enhanced toughness]
    E --> H[Non-load bearing, fire protection]

Summary: IS 2469 defines gypsum product terms; fire resistance depends on product type (Type-X), thickness, and additives. Special gypsum products include fibre concrete and partition blocks with specific uses