The alchemy of the lime cycle Lime (calcium oxide or calcium hydroxide) is a crucial ingredient in many traditional construction materials, for example when mixed with sand and water to form a flexible and breathable mortar. Lime mortar is essential to use in the repair and repointing of traditional stone buildings whereas cement-based mortar is inappropriate and should not be used. In this video, quicklime is being 'slaked' in a process that will produce lime plaster with its putty-like consist