plaster

Plaster

Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting, and can be easily manipulated with metal tools or even sandpaper. These characteristics make plaster suitable for a finishing, rather than a load-bearing material. The term plaster can refer to gypsum plaster (also known as //plaster of Paris//), lime plaster, or cement plaster.

Plaster is also used in architecture and art. When used in architecture, plaster can be used to create designs and complex detailing for enhancement in a room. The details can be anything from geometric to naturalistic. Also many of the greatest European artists such as Michelangelo, used plaster while creating famous arts. Plaster can take a whole different approach within art. Plaster can enhance certain paintings, or even change a perspective on the art. Plaster has also been used in medicine. For example such casts are made out of plaster. Plaster is used to support the broken bones and help them rebuild and grow back.

Types

Gypsum plaster/Plaster of Paris Gypsum plaster, or Plaster of Paris, is produced by heating gypsum to about 300°F (150 °C): CaSO4·2H2O + //Heat// → CaSO4·½H2O + 1½ H2O (released as steam). When the dry plaster powder is mixed with water, it re-forms into gypsum. If plaster or gypsum is heated above 200°C, anhydrite is formed, which will also re-form as gypsum if mixed with water. A large gypsum deposit at Montmartre in Paris led gypsum plaster to be commonly known as "plaster of Paris". Plasterers often use gypsum to simulate the appearance of surfaces of wood, stone, or metal, on in movie and theatrical sets for example. Nowadays, theatrical plasterers often use expanded polystyrene, although the job title remains unchanged.

Lime plaster Lime plaster is a mixture of calcium hydroxide and sand (or other inert fillers). Carbon dioxide in the atmosphere causes the plaster to set by transforming the calcium hydroxide into calcium carbonate (limestone). Whitewash is based on the same chemistry. To make lime plaster, limestone (calcium carbonate) is heated to produce quicklime (calcium oxide). Water is then added to produce slaked lime (calcium hydroxide), which is sold as a wet putty or a white powder. Additional water is added to form a paste prior to use. The paste may be stored in air-tight containers. Once exposed to the atmosphere, the calcium hydroxide turns back into calcium carbonate, causing the plaster to set. Lime plaster was a common building material for wall surfaces in a process known as lath and plaster, whereby a series of wooden strips on a studwork frame was covered with a semi-dry plaster that hardened into a surface. The plaster used in most lath and plaster construction was mainly lime plaster, with a cure time of about a month. To stabilize the lime plaster during curing, small amounts of plaster of Paris were incorporated into the mix. Because plaster of Paris sets quickly, "retardants" were used to slow setting time enough to allow workers to mix large working quantities of lime putty plaster. A modern form of this method uses expanded metal mesh over wood or metal structures, which allows a great freedom of design as it is adaptable to both simple and compound curves. Today this building method has been partly replaced with drywall, also composed mostly of gypsum plaster. In both these methods a primary advantage of the material is that it is resistant to a fire within a room and so can assist in reducing or eliminating structural damage or destruction provided the fire is promptly extinguished. Lime plaster is used for true frescoes. Pigments, diluted in water, are applied to the still wet plaster.

Cement plaster is a mixture of suitable plaster, sand, portland cement and water which is normally applied to masonry interiors and exteriors to achieve a smooth surface. Interior surfaces sometimes receive a final layer of gypsum plaster. Walls constructed with stock bricks are normally plastered while face brick walls are not plastered. Various cement-based plasters are also used as proprietary spray fireproofing products. These usually use vermiculite as lightweight aggregate. Heavy versions of such plasters are also in use for exterior fireproofing, to protect LPG vessels, pipe bridges and vessel skirts. Plaster is vital in the medical field. One of it's uses is for orthopedic casts because it can dry to mold to an injured area of the body really well. plaster is also used for immobilizing people with severe injuries and in dentistry, it is commonly used to mold teeth in order to provide models of teeth for fitting appliances like braces or dentures. Plaster is widely used as a support for broken bones; a bandage impregnated with plaster is moistened and then wrapped around the damaged limb, setting into a close-fitting yet easily removed tube, however, this is slowly being replaced by a fibreglass variety.Plaster is also used within radiotherapy when making [|immobilization casts] for patients. Plaster bandages are used when constructing an impression of the patients head and neck, and liquid plaster is used to fill the impression and produce a plaster bust. Perspex is then vacuum formed over this bust creating an immobilization shell.
 * Cement plaster **
 * Use of Plaster in Medicine**

The term **plaster** can refer to [|gypsum] plaster (also known as //**plaster of Paris**//), [|lime plaster], or [|cement plaster].
 * Plaster** is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to [|mortar] or [|cement] and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting, and can be easily manipulated with metal tools or even [|sandpaper] . These characteristics make plaster suitable for a finishing, rather than a load-bearing material.