• Danish: pudse, kalke, gipse
• Finnish: rapata

• Danish: klistre, overklistre
• Finnish: peittää, tapetoida, teipata

• French: plâtre

Danish

Noun

plaster

1. band-aid

Swedish

Noun

plaster

1. Indefinite plural of plast

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. 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). 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 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 limestone, causing the plaster to set.

Lime plaster is used for true frescoes. Pigments, diluted in water, are applied to the still wet plaster.

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. 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, the world over. 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.

Passive fire protection

Plasters have been in use in passive fire protection, as fireproofing products, for many decades.

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. 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. 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. 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. 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. Fireproofing plasters are closely related to firestop mortars. 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.

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.

Safety issues

The chemical reaction that occurs when plaster is mixed with water is exothermic in nature. 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. She subsequently had her thumbs and most of her fingers amputated. In place of plaster, alginate should be used for casting body parts.

Some variations of plaster that contain powdered silica or asbestos may present health hazards if inhaled. Asbestos is a known carcinogen when inhaled in powder form, especially in people who smoke, and inhalation can also cause asbestosis. Inhaled silica can cause silicosis and (in very rare cases) can encourage the development of cancer. 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. 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
• Italian plaster
• Intonaco
• Joint compound
• Limestone
• Passive fire protection
• Pargeting
• Plasterwork
• Polished plaster
• Ready-mix lightweight joint compound
• Stucco
• Venetian Plaster
• Wattle and daub

References

External links

• International Union of Bricklayers and Allied Craftworkers
• Plasterers Union
• on lime plastering techniques, Somerset UK

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