A typology of lime-based plasters from Iron age II until the Byzantine period in Jerusalem and its vicinity

Ancient lime-based plaster is a fine grain material, composed of lime as a binder and one or more types of aggregates or fillers. The lime consists mainly of the mineral calcite, but several other minerals are formed during its production: quick lime (calcium oxide) is produced while burning limestone, and once it absorbs humidity it turns into lime (calcium hydroxide), which then reacts chemically with atmospheric carbon dioxide to form calcite (calcium carbonate)-the main component of lime plaster. As only in rare cases were materials imported, the aggregate reflects the local availability of resources, and therefore, it is important to study the aggregate. Some aggregates are inert and do not interact with the lime; they act as fillers to improve mechanical properties. In the Jerusalem area, the local materials used are clay/soil, limestone chips, river gravel, flint and chalk; most of these materials do not react chemically with lime. Interestingly, manmade aggregates, such as crushed ceramics and charred ash do react chemically with lime in a hydraulic reaction, improving some mechanical and chemical properties.