Restoration of plasterwork
Introduction
Plaster, as an industrial product and construction material, is calcium sulfate hemihydrate (CaSO·½HO),[1] also known as baked plaster or plaster of Paris.[2] It is sold ground, in powder form, which once kneaded with water, can be used directly. Other chemical substances can be added to modify its setting characteristics, resistance, adhesion, water retention and density. The purest and finest grained form of industrial plaster is called plaster. Calcium sulfate hemihydrate also exists naturally: a rare and unstable mineral called bassanite.
It is made from a natural mineral also called gypsum or aljez "Plaster (mineral)") (calcium sulfate dihydrate: CaSO·2HO), by dehydration.
History
Plaster is one of the oldest materials used in construction. In the Neolithic period, with sedentarization, plaster began to be made by calcining aljez and using it to join the pieces of masonry, seal the joints of the walls and to cover the walls of the houses, replacing the clay mortar. In Çatal Hüyük, during the 9th millennium BC. C., we find plaster and lime trim, with remains of fresco paintings. In ancient Jericho, in the 6th millennium BC. C., molded plaster was used.
In Ancient Egypt, during the third millennium BC. C., plaster was used to seal the joints of the blocks of the Great Pyramid of Giza, and in many tombs as a covering and support for painted bas-reliefs. The palace of Knossos contains coverings and floors made of plaster.
The Greek writer Theophrastus, in his treatise on stone, describes gypsum (γύψος /gypsos/), its sites and ways of using it as plastering and for ornamentation. They also wrote about the applications of plaster by Cato and Columella. Pliny the Elder described its use in great detail. Vitruvius, Roman architect and writer, in his Ten Books on Architecture, describes gypsum (plaster), although the Romans normally used lime mortars and natural cements.
The Sassanids used plaster extensively in masonry. The Umayyads left signs of its use in their Syrian fortresses, as cladding and even in prefabricated arches.
Muslim culture spread the use of plaster in Spain, widely adopted in the Ebro valley and southern Aragon, leaving beautiful examples of its decorative use in the art of the areas of Aragon, Toledo, Granada and Seville.