Limewash is one of the simplest, but also one of the most effective, external “paint” treatments. It consists of a milk-like mixture of water and lime used to coat the exterior or interior surfaces of a structure. It has no added binding medium. Calcium oxide (quicklime) is made up as a slurry in water, and brushed directly onto the wall. As the water evaporates, the calcium oxide takes up carbon dioxide from the air and forms insoluble calcium carbonate. Slaked lime mixed with water will rub off rather easily. Traditionally, additional ingredients included glue, or size water, to bind and improve adhesion. Sometimes, common salt or calcium chloride would be added to tallow washes (Lime-tallow limewash) to assist the tallow to emulsify, and being hygroscopic would assist the carbonation of the lime on exposure. It is possible to tint limewash, using chemically inert pigments such as ochres and umbers, but limewashes are usually white. Synonyms: whitewash, whiting. Ashurst (1983); Trench (2000); RS Means Building Glossary (undated). [J. Cassar, R. de Angelis]