What is the maximum particle size allowed in aggregate for gypsum plaster?

Effectively 2.36 mm. No particles should be retained on the 2.36 mm IS Sieve (Table 1).

What is the permissible limit for clay and silt content?

The total content of clay, fine silt, and fine dust shall not exceed 5 percent by mass (Clause 5.1).

How do you test for organic impurities?

As per the test described in IS 2386 (Part 2). The aggregate fails the test if it produces a colour darker than the standard reference solution (Clause 5.2).

What is the required particle size distribution (grading)?

The grading must conform to the limits specified in Table 1, which provides percentage passing ranges for various IS Sieves from 2.36 mm down to 150 micron.

IS 9498

: 1980

inorganic aggregates for use in gypsum plaster

CurrentSpecializedSpecificationBIMMaterials Science · Building Limes and Gypsum Products

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This standard specifies the requirements for inorganic aggregates, such as sand or crushed stone sand, intended for use in gypsum plaster. It covers material properties, grading limits, and maximum permissible amounts of deleterious substances to ensure the quality and performance of the final plaster finish.

inorganic aggregates for use in gypsum plaster

Quick Reference Values

Max particle size0% retained on 2.36 mm IS Sieve

Min percentage passing 150 micron IS Sieve5%

Max percentage passing 150 micron IS Sieve20%

Max content of clay, fine silt, fine dust5% by mass

Practical Notes

The grading of the aggregate is critical for the workability and final texture of the plaster; using an aggregate that is too coarse will result in a rough, unworkable finish.

Ensure aggregates are free from organic impurities and excessive clay/silt, as these can negatively affect the setting time, strength, and may lead to surface defects.

This standard is only for aggregates used with gypsum-based plasters (e.g., IS 2547), not for traditional cement-sand plaster which uses aggregates specified in IS 383.