södra

Sádra refers to gypsum plaster, a white powder used in construction, sculpture, and medicine. It is produced by calcining gypsum rock (calcium sulfate dihydrate) to form calcium sulfate hemihydrate. When mixed with water, the hemihydrate rehydrates and hardens into calcium sulfate dihydrate, forming a solid mass.

In English-language contexts the material is often called plaster of Paris, a name that traces to historical gypsum deposits in Paris. The chemical process involves CaSO4·2H2O converting to CaSO4·0.5H2O during heating, and then reforming to CaSO4·2H2O as it sets when water is added. The setting reaction is slightly exothermic and produces a hard, brittle but workable mass.

Sádra has several notable properties: it is relatively inexpensive, easy to mix with water, and sets quickly to a smooth, moldable surface. It is noncombustible and offers good fire resistance and dimensional stability when cured. However, it is sensitive to moisture and has limited tensile strength, so it is typically protected from damp conditions in building applications.

Applications include interior plastering for walls and ceilings, decorative plasterwork and stucco, and mold making for sculptures and architectural elements. Medical uses include orthopedic casts and dental models, where accurate detail is important. Gypsum plaster can be mixed with fibers, lime, or cement for altered properties and durability, and surplus material can be recycled in some contexts.

Safety considerations involve avoiding inhalation of gypsum dust, using dust control measures during handling, and storing plaster in a dry environment to prevent premature setting. Environmentally, gypsum is relatively inert and widely recyclable through appropriate facilities.