Durability of air lime mortar

This contribution deals with the physical and chemical reasons why pure air lime mortars used in masonry of burned bricks exposed to outdoor climate have shown to be durable from the Middle Ages to our days. This sounds strange in modern times where pure air lime mortars are regarded as weak materials, which are omitted from standards for new masonry buildings, where use of hydraulic binders is prescribed.

The reasons for the durability seam to be two: 1. The old mortars have high lime contents. 2. The carbonation process creates a pore structure with a fine pored outer layer and coarser pores inside. This difference in pore size will delay the capillary suction of rain from outside, while excess water inside can be sucked to the front and evaporate.