What are the four types of gypsum plaster specified?

Type A (Plaster of Paris), Type B (Retarded hemihydrate), Type C (Anhydrous), and Type D (Keene's plaster).

What is the acceptable setting time for Plaster of Paris?

5 to 20 minutes as specified in Table 1.

Which code is used to conduct tests on these plasters?

IS 2542 (Part 1) outlines the methods of test for gypsum plasters.

IS 2547

: 2000

gypsum building plaster, Part 1: Excluding premixed lightweight plaster

CurrentFrequently UsedSpecificationMaterials Science · Building Limes and Gypsum Products

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This standard specifies the requirements for gypsum building plasters used for internal wall and ceiling finishes, excluding premixed lightweight varieties. It classifies plasters into four main types (Plaster of Paris, Retarded hemihydrate, Anhydrous, and Keene's) and sets criteria for setting time, soundness, compressive strength, and transverse strength.

gypsum building plaster, Part 1: Excluding premixed lightweight plaster

Quick Reference Values

Residue on 1.18mm IS Sieve0%

Setting time for Plaster of Paris (Type A)5 to 20 minutes

Minimum SO3 content35 percent by mass

Practical Notes

Gypsum plasters are strictly for internal use and should never be used in continuously damp or exposed external environments.

Type B (Retarded hemihydrate) is the most commonly used classification for standard interior wall leveling and finishing.

Improper storage exposes gypsum to moisture, leading to premature hydration, lumps, and drastically altered setting times.