Various advantages of lime-based mortars over Portland cement mortars are reported. The production of building lime consumes less energy, thus reducing greenhouse emissions compared to the equivalent manu facture of Portland cement. The subsequent car -bonation process removes CO2 from the atmosphere. Lime-based mortars remain sufficiently flexible to allow thermal and moisture movement, but, in addition, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. The recycling of bricks and blocks is easier due to the lower adherence of the mortar. Lime mortar construction is more breathable than Portland cement masonry and lime mortars are more resistant to sulphate attack than standard Portland cement mixes due to their lower tricalcium aluminate content.

Typical lime mortars are within the range 1 : 2 and 1 : 3, lime : aggregate ratio. A 1 : 2 lime : sand mix made with NHL3.5 lime equates approximately to the NA to BS EN 1996–1-1: 2005 designation (iii) class M4 mortar, and a 1 : 3 mix equates approximately to a designation (iv) class M2 Portland cement mortar. A well-graded sharp sand should be used. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints. Little hardening occurs at temperatures below 5°C.