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Building lime (Calcium Hydroxide or air lime) has been used in construction for thousands of years as a binder. The Romans were using air lime in combination with natural and artificial pozzolans in their buildings. Mortar formulations have developed over time and it was common practise in the last century to combine air lime and cement. In this way, lime has been used extensively as a component of masonry mortars and renders in order to provide the mason or bricklayer better mortar workability in the fresh state. These benefits essentially relate to the development of better water retention and air entrainment. In addition, as a result of the reaction with carbon dioxide from the air, the lime hardens and contributes to the overall strength of the mortar.
Although widely used, there is only a limited scientific or technical literature base that supports the beneficial attributes either in the fresh or hardened state. This paper reviews what literature is available and the types of benefits that lime brings to the performance of cement based mortars, not only in the fresh state, but also in the hardened state. This paper explores what evidence is in the literature and highlights the benefits of the use of lime in mortars.