Editing Plaster (section)

{{Short description|Broad range of building and sculpture materials}}
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{{about-distinguish|the type of building material and "plaster of Paris"|Concrete}}
{{other uses}}
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{{Use dmy dates|date=October 2022}}
[[File:Fontainebleau escalier roi5.jpg|thumb|[[Stucco]] plaster [[relief]]s, such as this work at the [[Château de Fontainebleau]], were hugely influential in [[Northern Mannerism]]. A plaster low-relief decorative [[frieze]] is above it.]]

'''Plaster''' is a [[building material]] used for the protective or decorative coating of walls and ceilings and for [[Molding (decorative)|moulding]] and casting decorative elements.<ref>''Plaster.'' In: {{cite book |date=2015 |editor1-last= Weyer |editor1-first=Angela |editor2-last=Roig Picazo |editor2-first=Pilar |editor3-last=Pop |editor3-first=Daniel |editor4-last=Cassar |editor4-first=JoAnn |editor5-last=Özköse |editor5-first= Aysun |editor6-last=Vallet |editor6-first=Jean-Marc |editor7-last=Srša |editor7-first= Ivan |title=EwaGlos. European Illustrated Glossary Of Conservation Terms For Wall Paintings And Architectural Surfaces. English Definitions with translations into Bulgarian, Croatian, French, German, Hungarian, Italian, Polish, Romanian, Spanish and Turkish. |url= http://elearn.hawk-hhg.de/projekte/ewaglos/pages/download.php |location=Petersberg |publisher=Michael Imhof |page=50 }}</ref> In English, "plaster" usually means a material used for the interiors of buildings, while "render" commonly refers to external applications.<ref>{{cite book |date=2011 |editor1-last=Henry |editor1-first=Alison |editor2-last=Stewart |editor2-first=John |title=English Heritage. Practical Building Conservation. Mortars, Renders & Plasters |location=Farnham / Burlington |publisher=Ashgate |page=87 }}</ref> The term [[stucco]] refers to [[plasterwork]] that is worked in some way to produce [[relief]] decoration, rather than flat surfaces.

The most common types of plaster mainly contain either [[gypsum]], [[lime plaster|lime]], or [[cement plaster|cement]],<ref name=Ullmanns>Franz Wirsching "Calcium Sulfate" in Ullmann's Encyclopedia of Industrial Chemistry, 2012 Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a04_555}}</ref> but all work in a similar way. The plaster is manufactured as a dry powder and is mixed with water to form a stiff but workable paste immediately before it is applied to the surface. The reaction with water liberates heat through [[crystallization]] and the hydrated plaster then hardens.

Plaster can be relatively easily worked with metal tools and [[sandpaper]] and can be moulded, either on site or in advance, and worked pieces can be put in place with [[adhesive]]. Plaster is suitable for finishing rather than load-bearing, and when thickly applied for decoration may require a hidden supporting framework.

Forms of plaster have several other uses. In medicine, plaster [[orthopedic cast]]s are still often used for supporting set broken bones. In dentistry, plaster is used to make dental models by pouring the material into [[dental impression]]s. Various types of models and moulds are made with plaster. In art, lime plaster is the traditional matrix for [[fresco]] painting; the pigments are applied to a thin wet top layer of plaster and fuse with it so that the painting is actually in coloured plaster. In the ancient world, as well as the sort of ornamental designs in plaster relief that are still used, plaster was also widely used to create large figurative reliefs for walls, though few of these have survived.