Editing Plaster (section)

==Types==
===Clay plaster===
{{further|Earthen plaster}}
[[File:Mud plaster over straw bales wall.jpg|thumb|Applying mud plaster to an outside wall]]
Clay plaster is a mixture of [[clay]], sand and water often with the addition of plant fibers for tensile strength over wood [[lath]].

Clay plaster has been used around the world at least since antiquity. Settlers in the American colonies used clay plaster on the interiors of their houses: "Interior plastering in the form of clay antedated even the building of houses of frame, and must have been visible in the inside of [[Wattle (construction)|wattle]] filling in those earliest frame houses in which … [[wainscot]] had not been indulged. Clay continued in use long after the adoption of laths and brick filling for the frame."<ref name="McKee">{{Cite book |title=An Introduction to Early American Masonry, Stone, Brick, Mortar and Plaster |last=McKee |first=Harvey J. |publisher=[[Association for Preservation Technology International]] |year=2017 |isbn=978-0-9986347-0-8 |location=Springfield, IL |pages=81}}</ref> Where lime was not easily accessible it was rationed and usually substituted with clay as a binder. In [[Martin E. Weaver]]'s seminal work he says, "Mud plaster consists of clay or earth which is mixed with water to give a 'plastic' or workable consistency. If the clay mixture is too plastic it will shrink, crack and distort on drying. Sand, fine gravels and fibres were added to reduce the concentrations of fine clay particles which were the cause of the excessive shrinkage."<ref name=conserving>{{Cite book|title=Conserving Buildings, A Manual of Techniques and Materials, Revised Edition|last=Weaver|first=Martin E. |publisher=Preservation Press|year=1997|isbn=978-0-471-50944-8|location=New York|pages=149}}</ref> Manure was often added for its fibre content. In some building techniques straw or grass was used as reinforcement.

In the Earliest European settlers' plasterwork, a mud plaster was used<!-- or more usually a mud-lime mixture << Questionable. Clay plaster was often covered with a finer layer of lime plaster. Mixing it with the clay usually does not improves the quality of the clay plaster enough to justify the expense for the lime.--><ref name=conserving /> McKee <ref name="McKee" /> wrote, of a circa 1675 Massachusetts contract that specified the plasterer, "Is to lath and siele<ref>{{Cite web |url={{Google books |N9I4AQAAMAAJ |plainurl=yes}} |title=A New Dictionary of the English Language |last=Richardson |first=Charles |date=1846 |access-date=4 December 2017}}</ref> the four rooms of the house betwixt the joists overhead with a coat of lime and haire upon the clay; also to fill the gable ends of the house with ricks and plaister them with clay. 5. To lath and plaster partitions of the house with clay and lime, and to fill, lath, and plaister them with lime and haire besides; and to siele and lath them overhead with lime; also to fill, lath, and plaster the kitchen up to the wall plate on every side. 6. The said Daniel Andrews is to find lime, bricks, clay, stone, haire, together with laborers and workmen."<ref>{{Cite book|title=The Colonial Architecture of Salem|url=https://archive.org/details/colonialarchite00unkngoog|last1=Cousins|first1=Frank|last2=Riley|first2=Phil M. |publisher=Little Brown and Company|year=1919|location=Boston |pages=39–40}}</ref> Records of the New Haven colony in 1641 mention clay and hay as well as lime and hair also. In German houses of Pennsylvania the use of clay persisted.<ref>{{Cite book|title=Domestic Architecture of American Colonies and the Early Republic|last=Kimbal|first=Sidney Fiske|publisher=Scribner's Sons|year=1922 |location=New York|pages=30}}</ref>

[[File:Clay plaster ceiling.jpg|thumb|Clay plaster base coat on split oak lath held in place with straw and manure, covered with a lime plaster top coat, [[Old Economy Village]], Pennsylvania (1827)]]

[[Old Economy Village]] is one such German settlement. The early Nineteenth-Century utopian village in present-day [[Ambridge, Pennsylvania|Ambridge]], Pennsylvania, used clay plaster substrate exclusively in the brick and wood frame high architecture of the Feast Hall, Great House and other large and commercial structures as well as in the brick, frame and log dwellings of the society members. The use of clay in plaster and in laying brickwork appears to have been a common practice at that time not just in the construction of Economy village when the settlement was founded in 1824. Specifications for the construction of, "Lock keepers houses on the [[Chesapeake and Ohio Canal National Historical Park|Chesapeake]] and Ohio Canal, written about 1828, require stone walls to be laid with clay mortar, excepting 3 inches on the outside of the walls … which (are) to be good lime mortar and well pointed."<ref>{{Cite book |title=An Introduction to Early American Masonry, Stone, Brick, Mortar and Plaster |last=McKee |first=Harley |publisher=Association of Preservation Technology |year=2017 |location=Springfield, IL |pages=61}}</ref> The choice of clay was because of its low cost, but also the availability. At Economy, [[root cellar]]s dug under the houses yielded clay and sand (stone), or the nearby Ohio river yielded washed sand from the [[Shoal|sand]] bars; and lime outcroppings and oyster shell for the [[lime kiln]].

The surrounding forests of the new village of Economy provided straight grain, old-[[Old-growth forest|growth]] oak trees for lath.<ref>Dendrochronology study, Geology Department, Wooster College, Wooster, Ohio. Study commissioned by Dennis Lapic, 2009. The study showed straight grained logs with first year of growth from 1662 to 1748, characteristic of trees of a virgin forest.</ref> Hand split lath starts with a log of straight grained wood of the required length. The log is split into quarters and then smaller and smaller bolts with wedges and a sledge. When small enough, a froe and mallet were used to split away narrow strips of lath<!-- - unattainable with field trees and their many limbs -->. Farm animals provided hair and manure for the float coat of plaster. Fields of wheat and grains provided straw and hay to reinforce the clay plaster. But there was no uniformity in clay plaster recipes.

[[Manure]] provides fiber for tensile strength as well as protein adhesive. Unlike [[casein]] used with lime plaster, hydrogen bonds of manure proteins are weakened by moisture.<ref>{{Cite report |title=Value-Added Chemicals from Animal Manure |last=Chen |first=Shulin |date=19 December 2003 |doi=10.2172/15009485 |citeseerx = 10.1.1.463.4548}}</ref> With braced timber-framed structures clay plaster was used on interior walls and ceilings as well as exterior walls as the wall cavity and exterior cladding isolated the clay plaster from moisture penetration. Application of clay plaster in brick structures risked water penetration from failed mortar joints on the exterior brick walls. In Economy Village, the rear and middle wythes of brick dwelling walls are laid in a clay and sand mortar with the front wythe bedded in a lime and sand mortar to provide a weather proof seal to protect from water penetration. This allowed a rendering of clay plaster and setting coat of thin lime and fine sand on exterior-walled rooms.

[[File:Clay, straw lime on wall lath closeup.jpg|thumb|Lime setting-coat on clay plaster with straw binder. Applied to hand-split lath over a timber framed wall of a brick family house at Old Economy Village, Pennsylvania]]

Split lath was nailed with square cut lath nails, one into each framing member. With hand split lath the plasterer had the luxury of making lath to fit the cavity being plastered. Lengths of lath two to six foot are not uncommon at Economy Village. Hand split lath is not uniform like sawn lath. The straightness or waviness of the grain affected the thickness or width of each lath, and thus the spacing of the lath. The clay plaster rough coat varied to cover the irregular lath. Window and door trim as well as the mudboard (baseboard) acted as screeds. With the variation of the lath thickness and use of coarse straw and manure, the clay coat of plaster was thick in comparison to later lime-only and gypsum plasters. In Economy Village, the lime top coats are thin veneers often an eighth inch or less attesting to the scarcity of limestone supplies there.

Clay plasters with their lack of tensile and compressive strength fell out of favor as industrial mining and technology advances in kiln production led to the exclusive use of lime and then gypsum in plaster applications. However, clay plasters still exist after hundreds of years clinging to split lath on rusty square nails. The wall variations and roughness reveal a hand-made and pleasing textured alternative to machine-made modern substrate finishes. But clay plaster finishes are rare and fleeting. According to Martin Weaver, "Many of North America's historic building interiors … are all too often … one of the first things to disappear in the frenzy of demolition of interiors which has unfortunately come to be a common companion to 'heritage preservation' in the guise of building rehabilitation."<ref name=conserving />

===Gypsum plaster (plaster of Paris){{anchor|Gypsum_plaster}}===
[[Gypsum]] plaster,<ref>{{Cite web |title=Gypsum plaster {{!}} building material |url=https://www.britannica.com/technology/gypsum-plaster |access-date=9 October 2020 |website=[[Encyclopedia Britannica]] |language=en}}</ref> also known as '''plaster of Paris''',<ref name="Britannica">{{Cite web |title=plaster of paris {{!}} Definition, Uses, & History |url=https://www.britannica.com/technology/plaster-of-paris |access-date=9 October 2020 |website=[[Encyclopedia Britannica]] |language=en}}</ref> is a white powder consisting of [[Calcium sulfate#Hydration and dehydration reactions|calcium sulfate hemihydrate]]. The natural form of the compound is the mineral [[bassanite]].<ref>{{Cite web|url=https://www.mindat.org/min-557.html|title = Bassanite}}</ref><ref>{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}</ref>

====Etymology====
The name "plaster of Paris" was given because it was originally made by heating gypsum from a large deposit at [[Montmartre]], a hill in the north end of [[Paris]].<ref name="Britannica" /><ref>{{Cite journal|last1=Szostakowski|first1=B.|last2=Smitham|first2=P.|last3=Khan|first3=W.S.|date=17 April 2017|title=Plaster of Paris–Short History of Casting and Injured Limb Immobilzation|journal=The Open Orthopaedics Journal|volume=11|pages=291–296|doi= 10.2174/1874325001711010291 |doi-access=free|issn=1874-3250|pmc=5420179|pmid=28567158}}</ref><ref>[http://www.yourdictionary.com/plaster-of-paris plaster of Paris definition. Webster's New World College Dictionary at YourDictionary.com.]</ref>

====Chemistry====
{{see also|Calcium sulfate#Hydration and dehydration reactions}}
Gypsum plaster, gypsum powder, or plaster of Paris, is produced by heating gypsum to about {{convert|120|–|180|C|F}} in a kiln:<ref name=lafarge>{{cite web|url=http://www.lafargeprestia.com/caso4___h2o.html |title=CaSO4, ½ H2O |last=Staff |publisher=[[Lafarge (company)|LaFargePrestia]] |access-date=27 November 2008 |url-status=dead |archive-url=https://web.archive.org/web/20081120163316/http://www.lafargeprestia.com/caso4___h2o.html |archive-date=20 November 2008 }}</ref><ref name="Britannica" />
<chem display="block">CaSO4.2H2O \overset{heat}{{}->{}} {CaSO4.1/2H2O} + 1\!1/2 H2O ^</chem>
(released as steam).

Plaster of Paris has a remarkable property of setting into a hard mass on wetting with water.

<chem display="block">CaSO4.1/2H2O + 1 1/2H2O -> CaSO4.2H2O</chem>

Plaster of Paris is stored in [[moisture]]-proof containers, because the presence of moisture can cause slow setting of plaster of Paris by bringing about its hydration, which will make it useless after some time.<ref name="Singh-2019" />

When the dry plaster powder is mixed with water, it rehydrates over time into gypsum. The setting of plaster slurry starts about 10 minutes after mixing and is complete in about 45 minutes. The setting of plaster of Paris is accompanied by a slight expansion of volume. It is used in making casts for statues, [[toy]]s, and more.<ref name="Singh-2019">{{Cite book|last1=Singh|first1=Lakhmir|title=Science for Class 10 Part-2 Chemistry|last2=Kaur|first2=Manjit|publisher=S. Chand|year=2019|isbn=978-9352837892}}</ref> The initial matrix consists mostly of orthorhombic crystals: the kinetic product. Over the next 72 hours, the rhombic crystals give way to an interlocking mass of monoclinic crystal needles, and the plaster increases in hardness and strength.<ref name="Schmidt">{{cite journal |quote=Hardening stage of plaster of paris is basically a crystalline change in which orthorhombic form of gypsum converts into the monoclinic form of gypsum.
|first1=V. E.
|last1=Schmidt
|first2=J. H.
|last2=Somerset
|first3=R. E.
|last3=Porter
|journal=Journal of Biomechanics
|publisher=Elsevier
|title=Mechanical Properties of Orthopeadic Plaster Bandages
|volume=6
|issue=2
|pages=173–185
|year=1973
|doi=10.1016/0021-9290(73)90086-9
|pmid=4693147
}}</ref> If plaster or gypsum is heated to between {{convert|130|and|180|°C|°F|abbr=on}}, [[hemihydrate]] is formed, which will also re-form as gypsum if mixed with water.<ref>Deer, Howie, & Zussman. ''An Introduction to the Rock Forming Minerals''. Pearson Education Limited, England, 2nd Edition, 1992, Page 614. {{ISBN|0-582-30094-0}}</ref><ref name="Posnjak">{{Citation
| last = Posnjak
| first = E.
| title = The System CaSO<sub>4</sub>–H<sub>2</sub>O
| year = 1938
| pages = 247–
| url = http://earth.geology.yale.edu/~ajs/1938-A/247.pdf
| quote = The long experience in the manufacture of plaster of Paris presents a consistent record that whenever gypsum is heated at not too high a temperature–usually about 130°–the product formed is invariably the hemihydrate; and further, that if the temperature is permitted to go considerably higher, the product becomes 'dead burned', it has then been converted into anhydrite.
}}</ref>

On heating to {{convert|180|°C|°F|abbr=on}}, the nearly water-free form, called γ-anhydrite (CaSO<sub>4</sub>·''n''H<sub>2</sub>O where ''n'' = 0 to 0.05) is produced. γ-anhydrite reacts slowly with water to return to the dihydrate state, a property exploited in some commercial [[desiccant]]s. On heating above {{convert|250|°C|°F|abbr=on}}, the completely anhydrous form called β-anhydrite or dead burned plaster is formed.<ref name="Singh-2019" /><ref name="Posnjak" />

====Uses of gypsum plaster====
{{Further information|Plaster#Applications}}
[[File:Cast extended.jpg|thumb|An [[orthopedic cast]] for the hand made out of plaster.]]
*for making surfaces like the walls of a house smooth before painting them and for making ornamental designs on the ceilings of houses and other buildings.<ref name="Singh-2019" /> ''(see [[#In decorative architecture|Plaster In decorative architecture]])''
*for making [[toy]]s, decorative materials, cheap ornaments, [[cosmetics]], and [[Blackboard|black-board]] [[chalk]].<ref name="Singh-2019" />
*a [[Fireproofing|fire-proofing]] material.<ref name="Singh-2019" /> ''(see [[#Fire protection|Plaster in Fire protection]])''
*an orthopedic cast is used in hospitals for setting [[Bone fracture|fractured bones]] in the right position to ensure correct healing and avoid [[nonunion]]. It keeps the fractured bone straight. It is used in this way, because when plaster of Paris is mixed with a proper quantity of water and applied around the fractured limb, it sets into a hard mass, thereby keeping the bones in a fixed position. It is also used for making casts in [[dentistry]].<ref name="Singh-2019" /> ''(see [[#Medicine|Plaster in Medicine]])''
*[[Laboratory|chemistry laboratory]] for sealing air-gaps in apparatus when air-tight arrangement is required.<ref name="Singh-2019" />

===Lime plaster===
{{Main|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 above approximately {{convert|850|°C|°F|abbr=on}} 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 airtight containers. When exposed to the atmosphere, the calcium hydroxide very slowly turns back into calcium carbonate through reaction with atmospheric carbon dioxide, causing the plaster to increase in strength.

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 [[Wall stud|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 [[fresco]]es, where [[pigment]]s, diluted in water, are applied to the still wet plaster.

USA and Iran are the main plaster producers in the world. {{citation needed|date=April 2015}}

===Cement plaster===
{{See also|Cement render}}
[[File:Plasterer at work on a wall arp.jpg|thumb|Plastering an internal wall]]
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 [[London stock brick|stock bricks]] are normally plastered while [[Brickwork|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.

Cement plaster was first introduced in America around 1909 and was often called by the generic name ''adamant plaster'' after a prominent manufacturer of the time. The advantages of cement plaster noted at that time were its strength, hardness, quick setting time and durability.<ref>Roberts, Isaac Phillips. ''The farmstead; the making of the rural home and the lay-out of the farm'',. 7th ed. New York: Macmillan Co., 1914. Print. 188.</ref>

===Heat-resistant plaster===
Heat-resistant plaster is a building material used for coating walls and chimney breasts and for use as a fire barrier in ceilings. Its purpose is to replace conventional gypsum plasters in cases where the temperature can get too high for gypsum plaster to stay on the wall or ceiling.

An example of a heat-resistant plaster composition is a mixture of [[Portland cement]], gypsum, lime, exfoliated insulating aggregate ([[perlite]] and [[vermiculite]] or [[mica]]), [[Phosphorite|phosphate shale]], and small amounts of adhesive binder (such as [[Gum karaya]]), and a detergent agent (such as [[Alkylbenzene sulfonates|sodium dodecylbenzene sulfonate]]).<ref name=heat>{{cite web|url=https://patents.google.com/patent/US3502490A/en |title=Heat and fire-resistant plaster compositions |publisher=Google Patents |access-date=9 November 2022 }}</ref>