Traditional Architectural Renders on Earthen Surfaces

Abstract

White or putty coat -(or sand finish) In addition to providing a flat, smooth and clean finished surface, the plaster is capable of being shaped either in place or in molds, in order to create an almost infmite variety of architectural decoration.Most traditional plasters contain clay, limealone or in combinationor gypsum as the principal binder always mixed with an aggregate such as sand or crushed stone; while traditional additives might vary depending on the products available in the area.Additives such as straw, animal hair or wood ashes have been commonly used in the past. Clay PlasterA soil is comprised of particles of diverse shapes and sizes.In order to determine its properties, granulometric definitions have been established according to various standards.These granulometric distinctions are based on equivalent particle diameters and are divided into gravel, sand, silt and clays.For this study the USA (ASTM Standards) ' will be followed:Clay -Particles with diameter < 5 um Silt -Particles with diameter 5 um -75 um Sand -Particles with diameter 75 um -4.75 mm Gravel -Particles with diameter 4.75 mm -76.2 mm Clays, the binding materials of soils, are chemically classified as hydrated aluminosilicates, containing as major components: sodium, potassium and calcium, varying amounts of iron oxide and smaller amounts of lime, manganese, alkalies and sulphur^.In their natural dry state they are found as fiber-like coagulated masses of molecules.When water is added to the mass, the layered molecules are arranged in parallel strata with water molecules held between the clay layers, causing the material to become plastic.This plasticity allows clays to be molded into almost any shape, which they retain when dry.If water is again added the molecules will disperse.The more active a clay is, the greater its capacity to swell and contract in the presence or absence of water.In terms of unbumt earthen building materials, the more stable the clay is, the less chance of cracking due to expansion and contraction.' ASTM 1139-83 :