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1、7PlasteringstrawbalesTheterm‘plaster’inthischapterisusedtorefertoallmixesofaggregatesandbinderstoformarelativelyhardtoveryhardcoatingonstrawbalewalls.‘Aggregates’maybefinetocoarsesandandothermaterials,andusuallyshouldbe‘sharp’,meaningroughandjaggedratherthansmoothrounde
2、dgrains.Binders,includingclay,limeandPortlandcement,bindtheaggregatestogether.Plasteror‘hardplaster’refersalsotosimilarmaterialthathasbeenusedsinceancienttimestomakemouldingsandotherdecorativefeaturesonbuildings.Modernplasteringthatinvolvesthefittingofplastersheetingand
3、pre-mademouldingsinmodernbuildingsisnotincludedinthecurrentdiscussion.‘Stucco’generallyreferstoaPortlandcement-basedplasterusedonexteriorwalls,especiallyinNorthAmerica,and‘render’isoftenusedinterchangeablywiththeterm‘plaster’.PlastertypesEarthenplastersandlimeplastersar
4、eincreasinglydisplacingcement-basedplasterforstrawbalewalls.Thishasbeenoccurringforvariousenvironmental,aestheticandperformancereasons,butsomebuilderswillstillprefertousecement,atleastforsomeenvironments.Theirreasonsforchoosingcement-basedplastersometimesarisefrominvali
5、dpreconceptions.Forexample,onemightchoosecement-basedplastertoachieveadurable,waterproofexternalfinish,but,forexample,despiteitsgenerallylowerstrength,limeplasterhasenduredformillenniaonsomeexternalwalls.1Therearealsovariousmeasuresthatcanbetakeninthedesignandchoiceofma
6、terialsthatwillachievethenecessarydurabilityandwaterproofingpropertiesformostapplications.1See:BMarchese(1980).Non-crystallineCa(OH)inancientnon-hydrauliclimemortars,Cement2andConcreteResearch,10:861–64.42PracticalstrawbalebuildingWallsthatbreatheItisgenerallyagreedthat
7、theplastershouldbeableto‘breathe’—i.e.itshouldbepermeabletowatervapourandair.Watervapourcanpermeatefairlyreadilythroughmostlimeandearthenplasters,butcement-basedplasterswithahighcementcontenttendtohavesubstantiallylowerbreathability.Excessivebuildupofmoistureinotherwall
8、types,suchastimberstudwallssheetedwithrelativelyimpermeablecladding,alsocanbeasubstantialproblemthatcanleadtos
