Low-grade gypsum use in the building industry-code of practice

IS 12654: Scope - Key Dimensions and Tolerances

• Nominal Dimensions of Blocks (Clause 8.2.1):

• Rounding Off (Clause 8.2):
  Values from tests or calculations must be rounded as per IS 2:1960 rules, retaining the same significant figures as specified.

• Physical Requirements (Clause 8.4):
  Specifies mandatory physical properties (not detailed here) to ensure block quality.

Summary:

• Blocks are standardized by length, breadth, and height with specified max and increments.
• Rounding rules ensure consistency in reporting.
• Physical properties ensure durability and performance.

flowchart TD
    A[IS 12654 Scope] --> B[Dimensions & Tolerances]
    B --> C[Length: ≤700 mm, multiples of 100]
    B --> D[Breadth: 75, 100, 125, 150 mm]
    B --> E[Height: ≤300 mm, multiples of 100]
    A --> F[Rounding: IS 2:1960]
    A --> G[Physical Requirements]

This ensures uniformity and quality control for blocks under IS 12654.

Referenced Standards in IS 12654

Key Indian Standards Adjunct to IS 12654 (Clause 2.1):

Rounding Off (IS 2:1960)

• Final test or analysis values must be rounded according to IS 2.
• Number of significant digits in the rounded value = number in the specified value.

Dimensions and Tolerances of Blocks (Clause 8.2.1)

Summary

• Use IS 2 for rounding numerical results.
• Refer to the listed IS codes for test methods and terminology.
• Block dimensions are standardized with specified tolerances.
• Compliance with these referenced standards ensures quality and uniformity.

flowchart TD
    A[IS 12654] --> B[IS 1288 - Mineral Gypsum Tests]
    A --> C[IS 2250 - Masonry Mortars]
    A --> D[IS 2469 - Gypsum Glossary]
    A --> E[IS 1/Sec 1-12 - Gypsum Plaster Tests]
    A --> F[IS 2542

IS 12654 - Definitions: Key Specifications and Dimensions

Clause 8.2.1: Nominal Dimensions of Blocks

• Length and Height: Maximum 700 mm and 300 mm respectively, must be in multiples of 100 mm.
• Breadth: Standardized at 75, 100, 125, or 150 mm.

Rounding Off (IS 2:1960)

• Final test or calculation values must be rounded off according to IS 2:1960.
• Retain the same number of significant figures as in the specified values.

Summary

• Blocks must conform to specified nominal sizes within tolerances.
• Physical and dimensional compliance is verified after rounding off results per IS 2.

flowchart TD
    A[Block Dimensions] --> B{Length}
    B -->|Max 700 mm| C[Multiples of 100 mm]
    A --> D{Breadth}
    D -->|75, 100, 125, 150 mm| E[Standard Sizes]
    A --> F{Height}
    F -->|Max 300 mm| G[Multiples of 100 mm]

This ensures uniformity and interchangeability of blocks as per IS 12654.

Purity of Gypsum (IS 12654)

• Minimum Purity: Low-grade gypsum must have not less than 60% purity as CaSO₄·2H₂O (gypsum dihydrate), per Clause 4.1.
• Impurities: Common impurities include silica, dolomite, and carbonates, which reduce purity.
• Test Method: Purity is determined according to IS 1288:1982.

Key Specifications for Low-Grade Gypsum Plaster (Table from Clause 7.1.1)

Notes:

• Gypsum plaster should be free from harmful materials like iron pyrites, alkali, organic impurities, mica, clay, etc.
• Purity affects strength and durability of the mortar.

flowchart LR
    A[Raw Gypsum] --> B[Purity Test (IS 1288)]
    B -->|≥ 60% CaSO4·2H2O| C[Acceptable for Use]
    B -->|< 60%| D[Reject or Process Further]
    C --> E[Preparation of Calcined Gypsum]
    E --> F[Gypsum Plaster Production]

This ensures quality gypsum plaster conforming to IS 12654 standards.

IS 12654: Preparation of Calcined Gypsum (Gypsum Plaster)

Key Specifications:

• Purity of low-grade gypsum: ≥ 60% CaSO4·2H2O (per IS 1288:1982)
• Major impurities: silica, dolomite, carbonates

Preparation (Clause 5):

• Calcined gypsum is produced by controlled heating of low-grade gypsum to remove part of the water of crystallization.
• The product is used in masonry mortar, internal plaster, and lightweight blocks.

Gypsum Plaster Requirements (Clause 7.1.1 & 8.1.1):

Gypsum plaster must conform to Table 1 (physical and chemical properties). Typical parameters include:

Important Notes:

• Controlled calcination temperature (~150-180°C) ensures proper reactivity.
• Overheating leads to dead-burnt gypsum (poor setting).
• Moisture content should be minimal to avoid premature setting.

flowchart LR
    A[Low-grade Gypsum] --> B[Calcination (150-180°C)]
    B --> C[Calcined Gypsum (Plaster)]
    C --> D{Uses}
    D --> E[Masonry Mortar]
    D --> F[Internal Plaster]
    D --> G[Lightweight Blocks]

This summarizes key preparation and quality criteria per IS 12654. For detailed Table 1 values, refer to the standard document.

IS 12654: Physical Requirements Summary

Key Dimensions (Clause 8.2.1 - Table 8.2)

Tolerances (Clause 8.2)

• The blocks must conform to specified dimensional tolerances to ensure uniformity.
• Typical tolerance: ±3 mm for length and breadth, ±5 mm for height (refer IS 12654 for exact values).

Physical Requirements (Clauses 7.4 & 8.4)

• Blocks should have uniform shape and size.
• Surface must be free from cracks, chips, and other defects.
• Density and water absorption must meet specified limits for durability.

Quick Reference:

Nominal Dimensions (mm):
- Length ≤ 700 (multiples of 100)
- Breadth = 75, 100, 125, or 150
- Height ≤ 300 (multiples of 100)

Tolerances:
- Length & Breadth: ±3 mm
- Height: ±5 mm

This ensures blocks are consistent for masonry work, aiding structural integrity and aesthetics.

IS 12654: Key Details on Gypsum Mortar

1. Gypsum Plaster Requirements (Clause 6.1 & 7.1.1)

• Must comply with Table 1 specifications (e.g., purity, setting time, fineness).
• Ensures quality for mortar use.

2. Gypsum Mortar Mix (Clause 7.5)

• Recommended mix:
  • 1 part gypsum plaster
  • 2 parts sand
  • 50% water (all by mass)
• Use for internal plastering and masonry only.
• Not suitable for external exposure except in very dry climates.

3. Compressive Strength (Clause 7.4.2)

• Gypsum mortar must have adequate compressive strength (specific values in IS 12654 Table or test procedures).
• Strength tested after setting, ensuring durability.

4. Performance Criteria (Clause 7.5)

• After 48 hours on brick surface, mortar should show:
  • No visible shrinkage cracks, chalking, or crazing
  • Good adhesion, no peeling after drying

Summary Table: Gypsum Mortar Mix & Properties

flowchart TD
    A[Gypsum Plaster] --> C[Gypsum Mortar Mix]
    B[Sand] --> C
    D[Water (50%)] --> C
    C --> E[Apply on Clean, Wetted Brick Surface]
    E --> F[Set for 48 Hours]
    F --> G{Check for Defects}
    G -->|No cracks, chalking, peeling| H[Acceptable Mortar]
    G -->|Defects Present| I[Reject or Rework]

This ensures gypsum mortar meets IS 12654 durability and application standards.

IS 12654: Light Weight Solid Gypsum Blocks for Non-Load Bearing Walls

Key Specifications (Clause 8)

• Application: Used exclusively for non-load bearing internal walls.
• Material: Calcined gypsum from low-grade gypsum.
• Block Type: Light weight solid gypsum blocks.

Physical Requirements (from Clause 6 & Table 1)

Gypsum Mortar (Clause 7.5)

• Mix Ratio:
  • 1 part gypsum plaster
  • 2 parts sand
  • 50% water (by mass)
• Application: Internal plastering & masonry only; avoid external exposure except in scanty rainfall areas.
• Performance: No shrinkage cracks, chalking, crazing after 48 hours; good adhesion without peeling.

Summary Formula for Mortar Mix

[ \text{Gypsum Mortar} = 1 \times \text{Gypsum Plaster} + 2 \times \text{Sand} + 0.5 \times \text{Water (mass fraction)} ]

flowchart LR
    A[Calcined Gypsum] --> B[Light Weight Solid Blocks]
    B --> C[Non-Load Bearing Walls]
    A --> D[Gypsum Mortar]
    D --> E[1 part Gypsum + 2 parts Sand + 50% Water]
    E --> F[Internal Plastering & Masonry]

Note: Always verify block dimensions and strength from supplier certificates as per IS 12654.

IS 12654: Method for Determination of Fineness of Gypsum Blocks

Key Specification:

• Fineness Requirement: Minimum 95% passing through 150 µm IS Sieve (Clause 7.1.1, Table 1)

Method (Annex A, Clause 1.1):

[ \text{Fineness (% passing)} = 100 - \left(\frac{\text{Mass retained on 150 µm sieve}}{100}\times 100\right) ]

Summary:

• Use 150 µm IS sieve
• Test duration: 5 minutes
• Fineness = % passing through sieve ≥ 95%

Additional Related Requirements (Table 1):

• Setting time: 10 to 30 minutes (IS 2542)
• Compressive strength: Minimum 7.0 N/mm² (IS 8272)

flowchart TD
    A[100 g dried sample] --> B[Sieve on 150 µm IS sieve for 5 min]
    B --> C[Break lumps gently]
    C --> D[Weigh retained material]
    D --> E[Calculate % passing = 100 - (retained mass %)]
    E --> F{Is fineness ≥ 95%?}
    F -- Yes --> G[Sample passes fineness test]
    F -- No --> H[Sample fails fineness test]

This ensures gypsum plaster quality per IS 12654.