Lime plaster Lime plaster Lime plaster is a type of plaster composed of sand, water, and lime, usually non-hydraulic hydrated lime (also known as slaked lime, high calcium lime or air lime). Ancient lime plaster often contained horse hair for reinforcement and pozzolan additives to reduce the working time. Traditional non-hydraulic hydrated lime only sets through carbonatation when the plaster is kept moist and access of CO from the air is possible. It will not set when submersed in water. When a very thick layer or several layers are applied, the lime can remain soft for weeks. The curing time of lime
Lime mortar contain dicalcium silicate but unlike Portland cement not tricalcium silicate. It is slaked enough to convert the calcium oxide to calcium hydroxide but not with sufficient water to react with the dicalcium silicate. It is this "dicalcium silicate" which in combination with water provides the setting properties of hydraulic lime. Aluminium and magnesium also produce a hydraulic set, and some pozzolans contain these elements. There are three strength grades for natural hydraulic lime, laid down in the European Norm EN459; NHL2, NHL3.5 and NHL5. The numbers stand for the minimum compressive strength at 28 days in newtons per square millimeter