Lime mortar is a type of building material made from a mixture of lime, water, and an aggregate like sand. It has been used for centuries in construction due to its flexibility and breathability, allowing buildings to adapt to changes in temperature and moisture. Lime mortar hardens over time through a process called carbonation, where it absorbs carbon dioxide from the air. Unlike modern cement, lime mortar is more environmentally friendly and can be easier to repair. It is commonly used in the restoration of historic buildings, as it helps preserve the original materials and techniques used in construction, ensuring the longevity of structures like cathedrals and castles.