Plaster of Paris, or simply plaster, is a type of building material based on calcium sulfate hemihydrate, nominally CaSO4·0. Calcium sulfate is a common laboratory and industrial chemical 5H2O. It is created by heating gypsum to about 150 °C. Gypsum is a very soft Mineral composed of Calcium sulfate dihydrate with the Chemical formula Ca[[sulfur S]] O 4·2
- 2 CaSO4·4H2O → 2 CaSO4·H2O + 3 H2O (released as steam).
A large gypsum deposit at Montmartre in Paris is the source of the name. Montmartre is a hill (the butte Montmartre) which is 130 metres high giving its name to the surrounding district in the north of Paris in the 18th Paris (ˈpærɨs in English; in French) is the Capital of France and the country's largest city [1] When the dry plaster powder is mixed with water, it re-forms into gypsum. Plaster is used as a building material similar to mortar or cement. Mortar is a workable paste formed by mixture of Cement, Water and fine aggregate Masonry to bind construction blocks together and fill the gaps between In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together Like those materials plaster starts as a dry powder that is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after drying, and can be easily manipulated with metal tools or even sandpaper. Mortar is a workable paste formed by mixture of Cement, Water and fine aggregate Masonry to bind construction blocks together and fill the gaps between In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together Abrasive Paper is a form of Paper where an Abrasive material has been fixed to its surface These characteristics make plaster suitable for a finishing, rather than a load-bearing material.
Plaster was a common building material for wall surfaces in a process known as lath and plaster, whereby a series of wooden strips are covered with a semi-dry plaster and then hardened into surface. The plaster used in most lath-and-plaster construction was mainly lime plaster. In the fields of Architecture and Civil engineering, construction is a process that consists of the Building or assembling of Infrastructure Lime plaster cure time is about a month. To stabilize the lime plaster during curing, small amounts of Plaster of Paris were mixed into the putty. 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.
One of the skills used in movie and theatrical sets is that of "plasterer", and the material is often used to simulate the appearance of surfaces of wood, stone, or metal. Nowadays, plasterers are just as likely to use expanded polystyrene, although the job title remains unchanged.
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Use in architecture
Plaster may also be used to create complex detailing for use in room interiors. These may be geometric (simulating wood or stone) or naturalistic (simulating leaves, vines, and flowers) These are also often used to simulate wood or stone detailing found in more substantial buildings.
Use in the arts
- See also: Plaster cast
Many of the greatest paintings in Europe, like Michelangelo's Sistine Chapel ceiling are executed in Fresco, meaning they are painted on a thin layer of wet plaster, called intonaco (in fact the general term for plaster in Italian); the pigments sink into this layer so that the plaster itself becomes the medium holding them, which accounts for the excellent durability of fresco. This article is on plaster copies made of sculptures and other objects The Sistine Chapel ceiling, painted by Michelangelo between 1508 and 1512 is one of the most renowned artworks of the High Renaissance. Fresco (plural either frescos or frescoes) is any of several related Painting types done on Plaster on walls or Intonaco is an Italian term for the final very thin layer of Plaster on which a Fresco wall painting is painted Additional work may be added a secco on top of the dry plaster, though this is generally less durable.
Plaster may be cast directly into a damp clay mold. In creating this moldmolds (molds designed for making multiple copies) or waste molds (for single use) would be made of plaster. This "negative" image, if properly designed, may be used to produce clay productions, which when fired in a kiln become terra cotta building decorations, or these may be used to create cast concrete sculptures. Terra cotta ( Italian: "baked earth" is a Ceramic. Its uses include vessels water & waste water pipes and surface embellishment in Building construction Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag If a plaster positive was desired this would be constructed or cast to form a durable image artwork. As a model for stonecutters this would be sufficient. If intended for producing a bronze casting the plaster positive could be further worked to produce smooth surfaces. An advantage of this plaster image is that it is relatively cheap; should a patron approve of the durable image and be willing to bear further expense, subsequent molds could be made for the creation of a wax image to be used in lost wax casting, a far more expensive process. Lost-wax casting, sometimes called by the French name of cire perdue, is the process by which a bronze is cast from an artist's sculpture in industrial uses the modern process In lieu of producing a bronze image suitable for outdoor use the plaster image may be painted to resemble a metal image; such sculptures are suitable only for presentation in a weather-protected environment.
Plaster expands while hardening, then contracts slightly just before hardening completely. This makes plaster excellent for use in molds, and it is often used as an artistic material for casting. Plaster is also commonly spread over an armature (form), usually made of wire, mesh or other materials.
Plaster is often used in Faux Finishing to create textures for wall and furniture surfaces, as in Venetian Plaster and also in stenciling for raised details. Faux painting or Faux finishing are terms used to describe a wide range of decorative painting techniques Venetian plaster (or Stucco Veneziano) is a Faux painting or faux finishing technique using thin layers of Plaster applied with a spatula or For these processes, artists use limestone based plasters or new user friendly acrylic based plaster.
Use in medicine
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, known as a Cast (orthopedic) cast; however, this is slowly being replaced by a fibreglass variety.
Plaster is also used within radiotherapy when making immobilisation 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 immobilisation shell.
In dentistry, plaster is used for mounting casts or models of oral tissues. These diagnostic and working models are usually made from dental stone, a stronger, harder and denser derivative of plaster which is manufactured from gypsum under pressure. Plaster is also used to invest or flask wax dentures, the wax being subsequently removed and replaced with the final denture base material which is cured in the plaster mold.
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). Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Whitewash is based on the same chemistry. Whitewash, or calcimine, kalsomine, or calsomine is a very low cost type of Paint made from Slaked lime (calcium hydroxide and
To make lime plaster, Limestone (calcium carbonate) is heated to produce quicklime (calcium oxide). Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Calcium oxide ( CaO) commonly known as burnt lime, lime or quicklime, is a widely used Chemical compound. Water is then added to produce slaked lime (calcium hydroxide), which is sold as a white powder. Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a Chemical compound with the chemical formula 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 limestone, causing the plaster to set.
Lime plaster is used for true frescoes. Fresco (plural either frescos or frescoes) is any of several related Painting types done on Plaster on walls or Pigments, diluted in water, are applied to the still wet plaster. For the drug referred to as "pigment" see Black tar heroin.
Cement 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. Portland cement is the most common type of Cement in general usage in many parts of the world as it is a basic ingredient of Concrete, mortar, Stucco 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. London stock brick is the most commonly used type of building Brick in London. Brickwork Masonry is produced when a Bricklayer uses Bricks and mortar to build up structures such as Walls Bridges and Various cement-based plasters are also used as proprietary spray fireproofing products, the world over. "Fireproof" redirects here For the album see Fireproof (album. These usually use vermiculite as lightweight aggregate. Vermiculite is a natural Mineral that expands with the application of Heat. Heavy versions of such plasters are also in use for exterior fireproofing, to protect LPG vessels, pipe bridges and vessel skirts.
Passive fire protection
Plasters have been in use in passive fire protection, as fireproofing products, for many decades. Passive fire protection (PFP is an integral component of the three components of structural Fire protection and fire safety in a Building. "Fireproof" redirects here For the album see Fireproof (album.
The plaster provides a layer of insulation to retard heat flow into structural steel elements, that would otherwise lose their strength and collapse in a fire. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Structural steel is Steel construction Material, a profile, formed with a specific Shape or cross section and certain standards of Early versions of these plasters have used asbestos fibres, which have by now been outlawed in industrialised nations and have caused significant removal and re-coating work. Asbestos is a group of Minerals with long thin fibrous Crystals The word "asbestos" (῾ἀσβεστος is derived from a Greek adjective Many buildings contain Asbestos, which was used in spray-applied Flame retardant, thermal system insulation and in a variety of other materials More modern plasters fall into the following categories:
- fibrous (including mineral wool)
- cement mixtures either with mineral wool or with vermiculite
- gypsum plasters, leavened with polystyrene beads, as well as chemical expansion agents to decrease the density of the finished product
One differentiates between interior and exterior fireproofing. Mineral wool, also known as mineral fibers or man-made mineral fibers are Fibers made from natural or synthetic Minerals or Metal Vermiculite is a natural Mineral that expands with the application of Heat. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Interior products are typically less substantial, with lower densities and lower cost. Exterior products have to withstand more extreme fire and other environmental conditions. Exterior products are also more likely to be attractively tooled, whereas their interior cousins are usually merely sprayed in place. A rough surface is typically forgiven inside of buildings as dropped ceilings often hide them. Exterior fireproofing plasters are losing ground to more costly intumescent and endothermic products, simply on technical merit. An intumescent is a substance which swells as a result of Heat exposure thus increasing in Volume, and decreasing in Density. In Thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs Energy in the form of Heat. Trade jurisdiction on unionised construction sites in North America remains with the plasterers, regardless of whether the plaster is decorative in nature or is used in passive fire protection. Cementitious and gypsum based plasters tend to be endothermic. In Thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs Energy in the form of Heat. Fireproofing plasters are closely related to firestop mortars. A firestop is a Passive fire protection System of various components used to seal openings and joints in fire-resistance rated wall In fact, most firestop mortars can be sprayed and tooled very well, due to the fine detail work that is required of firestopping, which leads their mix designers to utilise concrete addmixtures, that enable easier tooling than common mortars. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag
Trade jurisdiction
In unionized construction sites in North America, plaster is installed by contractors signatory to the Operative Plasterers’ and Cement Masons’ International Association (OPCMIA), which represents unionized plasterers. Template talkInfobox Union for usage -->The Operative Plasterers' and Cement Masons' International Association (OPCMIA of A Plasterer is a Tradesman who works with Plaster, such as forming a layer of plaster on an interior wall or plaster decorative moldings on ceilings or
Safety issues
The chemical reaction that occurs when plaster is mixed with water is exothermic in nature. In Thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases Energy usually in the form of Heat, but The danger of this was illustrated in January 2007, when a sixteen-year-old girl suffered third-degree burns after encasing her hands in plaster as part of a school art project in Lincolnshire, England. A school (from Greek σχολεῖον - scholeion) is an Institution designed to allow and encourage Students (or "pupils" Art refers to a diverse range of Human activities creations and expressions that are appealing to the Senses or Emotions of a human individual Lincolnshire (abbreviated Lincs) is a county in the east of England. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland She subsequently had her thumbs and most of her fingers amputated. [2] In place of plaster, alginate should be used for casting body parts. Alginic acid ( algin, alginate) is a viscous gum that is abundant in the cell walls of Brown algae.
Some variations of plaster that contain powdered silica or asbestos may present health hazards if inhaled. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Asbestos is a group of Minerals with long thin fibrous Crystals The word "asbestos" (῾ἀσβεστος is derived from a Greek adjective Asbestos is a known carcinogen when inhaled in powder form, especially in people who smoke, and inhalation can also cause asbestosis. The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation Asbestosis is a chronic inflammatory medical condition affecting the Parenchymal tissue of the Lungs It occurs after long-term heavy exposure Inhaled silica can cause silicosis and (in very rare cases) can encourage the development of cancer. Silicosis (also known as Grinder's disease and Potter's rot) is a form of Occupational lung disease caused by inhalation of crystalline Silica Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Persons working regularly with plaster containing these additives should take precautions to avoid inhaling powdered plaster, cured or uncured. (Note that asbestos is rarely used in modern plaster formulations because of its carcinogenic effects. )
Illegal Uses
Plaster of Paris has been used illegally by some professional boxers in the past, such as Luis Resto. Luis Resto (born September 21, 1960 in Juncos Puerto Rico) is a former Welterweight professional boxer from Bronx New York It makes a boxer's taped hands harder.
See also
- Cast Courts (Victoria and Albert Museum)
- Endothermic
- Fireproofing
- Firestop
- International Union of Bricklayers and Allied Craftworkers
- Intumescent
- Intonaco
- Joint compound
- Limestone
- Passive fire protection
- Pargeting
- Plasterwork
- Polished plaster
- Ready-mix lightweight joint compound
- Stucco
- Venetian Plaster
- Wattle and daub
References
- ^ plaster of Paris. The American Heritage® Dictionary of the English Language: Fourth Edition. 2000
- ^ BBC NEWS | Education | Amputation after art class burns
External links
- International Union of Bricklayers and Allied Craftworkers
- Plasterers Union
- on lime plastering techniques, Somerset UK
Dictionary
plaster
-noun
- (uncountable) A paste applied to the skin for healing or cosmetic purposes.
- (countable) (New Zealand, UK) A small adhesive bandage to cover a minor wound; a sticking plaster.
- (uncountable) A mixture of lime or gypsum, sand, and water, sometimes with the addition of fibres, that hardens to a smooth solid and is used for coating walls and ceilings.
- (countable) A cast made of plaster of Paris and gauze; plaster cast.
-verb
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