Lime cures by a carbonation process involving carbon dioxide from the air. It is much slower than the cement hydration reaction. Complete curing can take many months and the final strength is far less than that achieved by cement. Lime mortars also have a higher degree of porosity than cement mortars. The carbonation of lime, a very slow process under optimum conditions, is, like the hydration of cement, retarded by winter temperatures.
Water serves a dual purpose in masonry mortars.
It is required for the hydration of the cement and it provides the degree of workability necessary for the mortar to flow into all the cracks and crevices of the unit and form the maximum bond. More water is required for the latter purpose than for the hydration reaction. Thus, following placement in a wall, masonry mortars are low in strength and high in water content. This vulnerable period is prolonged in winter by slower curing at lower temperatures. Natural stone, clay brick and tile, concrete brick and block are all porous, and when they come into contact with mortar they immediately start to extract water by capillary suction.