GYPSUM BUILDING PLASTER

GYPSUM BUILDING PLASTER

Gypsum building plaster is the white or grayish subsieve powder obtained from gypsum stone (rock gypsum) by baking at a temperature of of 140-190 °C; quick-setting and quick-hardening binding agent.

Quick setting (hardening) of gypsum building mortars is not always convenient. When working with gypsum mortars it should be remembered that hardening gypsum paste rejuvenates during mixing and ceases to set. Such mortar applied to surface has no strength – there occur cracks in setting and coating damages. Gypsum mortars shall be prepared a little at a time (so called plaster formations) to be applied within several minutes.

Lime mortar or clay mud or special retarding agent of of 0.5-2% of sodium borate solution (all solutions shall be prepared with water) shall be added to retard the setting. Hardened gypsum is characterized by high strength and relatively low density (1200-1500 kg/m3); it is lighter than hardened cement more than in 2 times, consequently, it is less thermally conductive.

Gypsum is made of natural gypsum stone by its crushing, steaming in autoclaves, drying and grinding in ball mills with the subsequent separation in a separator. Natural anhydrite (CaS04) and chemical production residuals –   phosphogypsum and borogypsum can be used except rock gypsum. Gypsum has unique property – when heating up to 120-140 °C chemically combined water is exuded from crystal lattice forming semi-burned gypsum or alabaster, but gypsum building plaster (burned) is obtained at higher temperatures.

Gypsum building plaster is used for manufacturing of artificial marble and some of paints and chalks, as well as fixation of glassware during their polishing, e.g., in the manufacture of mirror and optical glass. Gypsum, in mixture with asbestos and other materials, is a part of thermal insulating compositions.

By means of this it was possible to develop the methods of gypsum binding material G-4 and G-5 production with representative characteristics of setting time and ultimate compressing/bending strength.

Gypsum Building Plaster Physiochemical Parameters: