ABSTRACT
Until the 1950s most plasterwork was based on lime. Lime is made from chalk or limestone (calcium carbonate), which was (and still is) heated in kilns to drive off the carbon dioxide. The resultant material, quicklime, was then added to water (slaking) to produce calcium hydroxide. When the slaking was complete, the mix was run through sieves to screen out any unslaked lime. It was then stored in large pits where it was usually kept at least two or three months before being used to ensure the slaking was complete. The lime preferred for plastering was known as pure lime or ‘fat’ lime. It contained no impurities (which might speed up the set). The best limes are from Crich, Buxton and Dorking. The lime was mixed with sands, ash and other fine aggregates and then applied to the background in two or three coats. The plaster hardened by drying and by absorbing carbon dioxide from the atmosphere. This was a very slow process — it could take several months before the plaster was hard enough to paper or decorate.
