gypsum plaster for use in the manufacture of fibrous plaster boards

IS 8272: Scope - Key Specifications & Formulas

Scope Summary: IS 8272 covers the standard testing consistency of plaster, defining test methods and criteria for setting time, compressive strength, and fineness.

Key Specifications:

Important Formulas:

• Consistency Range Check (Clause 4.4.1):

[ X \pm 0.4R ]

Where:

• (X) = average of test results
• (R) = range of test results

The lower limit (X - 0.4R) must be ≥ minimum specified, and the upper limit (X + 0.4R) ≤ maximum specified.

Testing Consistency Method (Appendix F):

• Use Ring Mould for spread test.
• Measure spread diameter after mixing plaster with water.
• Adjust water to reach standard consistency (spread diameter within 100 ± 3 mm).

flowchart LR
    A[Prepare plaster sample] --> B[Add water incrementally]
    B --> C[Place in Ring Mould (35 mm dia, 50 mm height)]
    C --> D[Measure spread diameter]
    D --> E{Diameter within 97-103 mm?}
    E -- Yes --> F[Standard Testing Consistency achieved]
    E -- No --> B

This scope ensures uniformity and reliability in plaster testing per IS 8272.

IS 8272: Materials and Classification - Key Points

1. Standard Consistency (Clause 3.1, Appendix F)

• Ring Mould Dimensions:
  • Internal diameter = 35 mm
  • Height = 50 mm
• Standard Consistency Definition:
  Mixture is at standard consistency if the average spread diameter (max + min)/2 = 100 ± 3 mm.
• Expression for Consistency:
  Water added (ml) per 100 g of plaster to achieve this spread.

2. Compressive Strength Test (Clause 3.2, Appendix D)

• Test specimens prepared as per Appendix D.
• Strength determined by compressive testing on standard specimens.

3. Statistical Evaluation of Test Results (Clause 4.4.1)

• For setting time, compressive strength, and fineness:

  [ X \pm 0.4R ]

  • (X) = average value
  • (R) = range

• Acceptance criteria:
  [ X - 0.4R \geq \text{minimum limit}, \quad X + 0.4R \leq \text{maximum limit} ]

Summary Table: Ring Mould Dimensions

This ensures uniformity in testing plaster materials for quality control as per IS 8272.

IS 8272: Key Requirements and Formulas

1. Criteria for Conformity (Clause 4.4 & 4.4.1)

• For test results (setting time, compressive strength, fineness), calculate:

  • Average (X)
  • Range (R)

• Check using the expression:

  [ X \pm 0.4R ]

• Conditions:

  • (X - 0.4R \geq) minimum specified limit
  • (X + 0.4R \leq) maximum specified limit

If these are satisfied, the lot conforms to the standard.

2. Ring Mould Specifications (Appendix F, Clause F-1.1)

• Used for standard consistency testing.
• Material: Non-absorbent, corrosion-resistant.
• Dimensions:

Summary Diagram

flowchart TD
    A[Test Results] --> B[Calculate Average (X) and Range (R)]
    B --> C[Compute X ± 0.4R]
    C --> D{Check Limits}
    D -->|X - 0.4R ≥ Min Limit| E[Pass Minimum Limit]
    D -->|X + 0.4R ≤ Max Limit| F[Pass Maximum Limit]
    E & F --> G[Lot Conforms]

This method ensures consistent quality control per IS 8272.

IS 8272: Sampling and Criteria for Conformity

Sampling (Clause 4.2 & Table 1)

• Number of packages to select depends on lot size:

• Packages must be selected randomly (Clause 4.2.1), following procedures in IS 4905-1968 to ensure unbiased sampling.

Criteria for Conformity (Clause 4.4)

• A lot is conforming if it meets conditions in Clauses 4.4.1 and 4.4.2 (typically related to test results within permissible limits).
• Samples are tested separately from each lot (Clause 4.1.1) to verify compliance.

Summary Flowchart for Sampling & Conformity

flowchart TD
    A[Start: Identify Lot Size] --> B{Lot Size?}
    B -->|Up to 100| C[Select 3 packages]
    B -->|101 to 150| D[Select 4 packages]
    B -->|151 to 300| E[Select 5 packages]
    B -->|301 to 500| F[Select 7 packages]
    B -->|501 and above| G[Select 10 packages]
    C --> H[Random selection per IS 4905]
    D --> H
    E --> H
    F --> H
    G --> H
    H --> I[Test samples]
    I --> J{Meets Clause 4.4.1 & 4.4.2?}
    J -->|Yes| K[Lot Conforms]
    J -->|No| L[Lot Rejected]

Note: Refer to IS 8272 for detailed testing criteria in Clauses 4.4.1 and 4.4.2.

IS 8272: Packaging and Marking Key Points

Sampling (Clause 4.2 & Table 1)

Number of packages to sample from a lot based on lot size:

Packaging (Clause 5.1)

• Plaster must be dry, free from lumps, and packed in water-tight bags or containers.

Marking (Clause 5.1 & 5.1.1)

Each package shall be legibly marked with:

• Name of manufacturer
• Class of plaster
• Date of manufacture

Additionally:

• ISI Certification Mark may be used following the Indian Standards Institution's regulations, ensuring compliance and quality control.

flowchart LR
    A[Lot Size] --> B[Select Sample Size as per Table 1]
    B --> C[Packaging]
    C --> D[Dry, Lump-free Plaster]
    D --> E[Pack in Water-tight Bags]
    E --> F[Marking]
    F --> G[Manufacturer Name]
    F --> H[Class of Plaster]
    F --> I[Date of Manufacture]
    F --> J[Optional: ISI Certification Mark]

This ensures quality, traceability, and compliance with IS 8272 standards.

IS 8272: Method for Determination of Impurities Insoluble in Ammonium Acetate Solution

Key Specifications & Procedure (Appendix A, Clause 2.2)

• Limit: Impurities insoluble in ammonium acetate ≤ 10% by mass.

• Sample Preparation: Grind sample to pass through 250 µm IS sieve.

• Sample Size: Take 4 g dried sample.

• Solution: Add 350 ml ammonium acetate solution.

• Heating: Heat at approx. 70°C for 30 minutes, stirring frequently.

• pH: Keep alkaline with ammonia (phenolphthalein indicator).

• Filter Aid: Add 2 g diatomaceous silica (optional) to facilitate filtration.

• Filtration: Use suction through a tared Gooch crucible.

• Washing: Wash filtrate with warm ammonium acetate, then with warm ammonium hydroxide.

• Drying: Dry crucible + residue at 70°C to constant mass, cool in desiccator.

• Calculation:
  [ % \text{Impurities Insoluble} = \frac{(m_2 - m_1) - m_a}{m_s} \times 100 ]

  Where:

  • (m_2) = mass of crucible + residue after drying
  • (m_1) = mass of empty crucible
  • (m_a) = mass of filter aid (if used)
  • (m_s) = mass of dried sample (4 g)

Summary Table

flowchart TD
    A[Sample Grinding] --> B[Weigh 4 g Sample]
    B --> C[Add 350 ml Ammonium

IS 8272: Method for Determination of Chloride Content in Plaster

Key Steps (Appendix B, Clause 2.3 & 3.1):

1. Sample Preparation:

   • Weigh 1 to 6 g of plaster sample.
   • Add 5 to 20 ml of 0.05 N silver nitrate (AgNO3) solution (2-3 ml excess beyond stoichiometric requirement).
   • Add strong nitric acid (25:100) carefully.
   • Heat gently and stir until plaster dissolves.
   • Add 100 ml hot water, digest 5 minutes, stir occasionally.
   • Filter through Buchner funnel.

2. Calculation:

   • 1 ml of 0.05 N AgNO3 ≡ 0.002923 g NaCl.
   • Chloride content (%) =
     [ \frac{\text{Average ml of AgNO}_3 \times 0.002923 \times 100}{\text{Weight of sample (g)}} ]

3. Reporting:

   • Average of 3 tests reported.
   • Chloride content must not exceed 0.2% (Clause 2.3).

Summary Table:

flowchart TD
    A[Weigh Sample (1-6g)] --> B[Add 0.05 N AgNO3 (5-20 ml)]
    B --> C[Add Strong Nitric Acid]
    C --> D[Heat & Stir until dissolved]
    D --> E[Add 100 ml Hot Water]
    E --> F[Digest 5 mins & Stir]
    F --> G[Filter (Buchner Funnel)]
    G --> H[Calculate Chloride Content]

This method ensures precise chloride quantification critical for plaster quality control.

IS 8272 Sampling Procedures Summary

1. Sample Size Selection (Clause 4.2 & Table 1)

• Packages must be randomly selected (Clause 4.2.1).
• Use IS 4905-1968 for random sampling methods.

2. Composite Sample Preparation (Clause 4.3.2)

• Mix equal quantities of gypsum plaster from each selected package.
• Conduct tests on this composite sample.

3. Sample Grinding & Testing (Clause 2.1)

• Grind sample to pass through 250 µm IS Sieve.
• Take 4 g dried sample + 350 ml ammonium acetate solution.
• Heat at ~70°C for 30 min with stirring.
• Add 2 g diatomaceous silica if needed for filtration.
• Keep solution alkaline (phenolphthalein indicator).
• Filter through Gooch crucible, wash, dry at 70°C, cool, weigh.
• Subtract filter aid mass if used.

This ensures statistically valid, representative sampling and accurate test results per IS 8272.

IS 8272: Compressive Strength Test Method - Key Points

Test Specimen Preparation (Clause D-1, 2.1)

• Cube specimens dried, then cooled at room temperature for 15 minutes before testing.
• Loading rate: specimen failure between 20 to 80 seconds.

Compressive Strength Calculation (Clause 3.1)

• Test 5 cubes; average compressive strength = reported strength.
• Discard 1 or 2 cubes if their strength differs by more than ±15% from the average.
• Report average of remaining cubes.

Statistical Evaluation (Clause 4.4.1)

Calculate:

• Average, ( X )
• Range, ( R )

Ensure: [ X - 0.4R \geq \text{minimum specified strength} ] [ X + 0.4R \leq \text{maximum specified strength} ]

Summary Table for Compressive Strength Test

flowchart TD
    A[Prepare 5 Cube Specimens] --> B[Dry & Cool 15 min]
    B --> C[Apply Compression Load]
    C --> D{Load Time 20-80 sec?}
    D -- Yes --> E[Record Strength of Each Cube]
    D -- No --> F[Adjust Loading Rate]
    E --> G[Calculate Average (X) & Range (R)]
    G --> H{Any Cube > ±15% from X?}
    H -- Yes --> I[Discard Outliers]
    H -- No --> J[Calculate \(X \pm 0.4R\)]
    J --> K{Within Limits?}
    K -- Yes --> L[Report Compressive Strength]
    K -- No --> M[Retest or Reject Sample]

This ensures reliable, standardized compressive strength measurement per IS 8272.

IS 8272: Method for Determination of Setting Time (Appendix E)

Key Steps (Clause E-2.1):

• Prepare plaster-water mix at standard consistency (per Appendix F).
• Transfer to setting dish, level to 10 mm depth.
• Make incisions 10 mm deep, 50 mm long at intervals until stiffening begins.
• Continue at 1-minute intervals until incisions remain open fully (indicating stiffening).

Setting Time Limits (Clause 3.3.1):

• Initial Setting Time: 20 to 35 minutes (unless otherwise agreed).

Statistical Evaluation (Clause 4.4.1):

• Calculate average (X) and range (R) of test results.
• Calculate:
  [ X \pm 0.4R ]
• Check:
  [ X - 0.4R \geq \text{Minimum limit} ] [ X + 0.4R \leq \text{Maximum limit} ]

Summary Table:

flowchart TD
    A[Prepare mix at standard consistency] --> B[Transfer to setting dish (10 mm depth)]
    B --> C[Make incisions (10 mm deep, 50 mm long)]
    C --> D{Incisions remain open fully?}
    D -- No --> C
    D -- Yes --> E[Record setting time]

This method ensures consistent and reproducible setting time measurement for gypsum plaster.

IS 8272: Method for Determination of Standard Testing Consistency

Key Specifications:

• Ring Mould Dimensions (Appendix F-1.1):
  • Internal diameter = 35 mm
  • Height (length) = 50 mm
  • Material: Non-absorbent, corrosion-resistant

Standard Testing Consistency (Clause 3.1):

• The plaster-water mixture is considered at standard testing consistency if the average of the max and min diameters of the spread (measured as per F-2) is within 100 ± 3 mm.
• Expressed as the volume of water (in ml) added to 100 g of plaster to achieve this spread.

Testing Procedure Summary:

1. Mix plaster with water by method F-2.2.
2. Place in ring mould.
3. Measure spread diameters after lifting mould.
4. Calculate average diameter: [ D_{avg} = \frac{D_{max} + D_{min}}{2} ]
5. Adjust water content until ( D_{avg} = 100 \pm 3 \text{ mm} ).

Table: Standard Consistency Limits

flowchart TD
    A[Prepare plaster-water mix] --> B[Place mix in ring mould (35 mm dia, 50 mm height)]
    B --> C[Lift mould and measure spread diameters]
    C --> D[Calculate average diameter]
    D --> E{Is average within 97-103 mm?}
    E -- No --> F[Adjust water content and remix]
    F --> A
    E -- Yes --> G[Record water quantity as standard consistency]

This method ensures reproducible plaster mix consistency for further testing like setting time.