Gypsum (CaSO4•2H2O) is a naturally hydrated Calcium Sulphate and is only slightly soluble in water. Gypsum is used as the source of calcium in clear-water drilling and in other inhibitive mud systems.
Gypsum is hygroscopic; therefore it should be stored in a dry environment to avoid lumping and hardening. It is advisable to use a dust mask and eye protection while mixing all powdered products. A dust hazard is present while gypsum is being mixed.