Lime Plaster
Lime plaster is a mixture of calcium hydroxide and sand (or other inert fillers).
Carbon dioxide in the atmosphere causes the plaster to set by transforming the calcium hydroxide into calcium carbonate (limestone).
Whitewash is based on the same chemistry.
To make lime plaster, Limestone (calcium carbonate) is heated to produce quicklime (calcium oxide). Water is then added to produce slaked lime (calcium hydroxide), which is sold as a white powder. Additional water is added to form a paste prior to use.
The paste may be stored in air tight containers.
Once exposed to the atmosphere, the calcium hydroxide turns back into
limestone, causing the plaster to set.
Lime plaster is used for true frescoes.
Pigments, diluted in water, are applied to the still wet plaster