What defines 'low-grade' gypsum in this standard?

Gypsum mineral (CaSO4.2H2O) content not less than 70 percent by mass.

What is the minimum compressive strength required for this type of plaster?

A minimum of 6.0 N/mm² after 7 days of curing (as per Table 1).

What are the acceptable setting times?

Initial setting time must be a minimum of 20 minutes, and the final setting time must be a maximum of 180 minutes (3 hours).

Can plaster made from low-grade gypsum be used for structural purposes?

No, this code covers its use for non-structural applications like internal plastering, non-load bearing partition blocks, and ceiling boards.

IS 12654

: 1989

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

CurrentSpecializedCode of PracticeMaterials Science · Building Limes and Gypsum Products

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This standard outlines the code of practice for utilizing low-grade gypsum in the building industry. It specifies the requirements, testing, and application methods for gypsum plaster, partition blocks, and other building components derived from gypsum with a purity of 70% or more.

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

Quick Reference Values

Minimum Gypsum (CaSO4.2H2O) Content70% by mass

Minimum Initial Setting Time20 minutes

Maximum Final Setting Time180 minutes

Minimum Compressive Strength (7 days)6.0 N/mm²

Residue on 150-micron IS SieveMax 1.0% by mass

Practical Notes

The performance of plaster from low-grade gypsum is sensitive to impurities; batch testing for setting time and strength is highly recommended.

Not suitable for external plastering or areas with continuous dampness or high humidity without appropriate waterproofing treatment.

Ensure proper surface preparation (cleaning, roughening, and wetting) before application to achieve good adhesion and prevent delamination.