What is the minimum purity requirement for by-product gypsum?

The minimum Calcium Sulphate (CaSO₄·2H₂O) content must be 85.0 percent by mass (Table 1).

What is the required initial setting time for this type of gypsum?

The initial setting time must be a minimum of 20 minutes as per testing (Table 2).

Is there a limit on fineness?

Yes, the residue retained on a 150-micron IS Sieve must not exceed 5.0 percent by mass (Table 2).

What are the main types of by-product gypsum covered?

The standard primarily covers phosphogypsum (from phosphoric acid production) and fluoro-gypsum (from hydrofluoric acid production).

IS 12679

: 1989

By-product gypsum for use in plaster, blocks and boards

CurrentSpecializedSpecificationBIMMaterials Science · Building Limes and Gypsum Products

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This standard lays down the requirements for by-product gypsum, such as phosphogypsum and fluoro-gypsum, intended for use in the manufacture of building materials like plasters, blocks, and boards. It specifies the necessary chemical composition and physical properties to ensure the quality and performance of the final products.

By-product gypsum for use in plaster, blocks and boards

Quick Reference Values

Minimum Calcium Sulphate (CaSO₄·2H₂O) content85.0 % by mass

Maximum Chloride (as Cl) content0.1 % by mass

Maximum Fluoride (as F) content1.0 % by mass

Fineness (residue on 150-micron sieve)5.0 % by mass max

Initial Setting Time20 minutes min

Final Setting Time30 minutes max

Practical Notes

By-product gypsum originates from industrial processes (e.g., fertilizer plants, power plants), so its impurity profile can vary. Testing against Table 1 for contaminants like chlorides and fluorides is critical.

The setting time requirements (20 min initial, 30 min final) are for the raw gypsum material itself, not the final plaster product, which will have retarders added to extend working time.

This gypsum is primarily used for non-structural interior applications like partition walls and false ceilings.