Special Materials Used In Plastering

Lesson 26 : Plastering And Pointing

Special Materials Used In Plastering

Plaster of Paris: It is also known calcium sulphate plaster and is obtained by heating Gypsum. Gypsum occurs in the form of natural rock which is usually composed of one part of calcium sulphate and two parts of chemically combined water of crystallization. When the water of crystallization is driven off from gypsum stone through calcinations or heat treatment, it forms a plastic mass, which sets rapidly. Plaster of paris adheres well to gypsum, wood, metal lath, masonry or other plastering surfaces. The setting time of the plaster of paris can be controlled by the addition of certain salts. It is mostly used in combination with ordinary lime, for making good, small defects in plastered surfaces. Since gypsum is slightly soluble in water, plaster of paris is not used for external works.

Keene’s Cement: This is hardest and densest form of gypsum plaster. It is obtained by calcining selected form of gypsum. It is pure white in color and takes a high glass like polish. It is used for highly decorative plastering work and ornamental work. It is used alone for extra – hard finish or it is mixed with lime putty for medium hard finish.

Barium plaster: This is essentially made from barium sulphate and is applied in the form of final coat to serve as a protection around X-ray rooms.

Acoustical plaster: It is gypsum mixture, which is employed as a final coat to serve the purpose of a sound – repellent finish. The minute passages in the form of tiny openings in the plaster coat, absorb sound. The plaster is usually applied in two coats, each 6 mm. in thickness. The surface must be finished uniformly in a manner that promotes porocity. Wooden float is preferred to a steel trowel in finishing.

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Last modified: Friday, 20 April 2012, 5:37 AM