How lime works

How lime works

Lime stone or calcium carbonate is burnt in a kiln to 900°, losing all of its water and carbon dioxide and becoming calcium oxide or quick lime.

Slaked with water, this thirsty material becomes calcium hydroxide, otherwise known as air lime or lime putty.

Once exposed to the air, calcium hydroxide takes back the carbon dioxide lost in the kiln and turns itself back into calcium carbonate.

This elegant cycle, known as carbonation, gives us the most permeable, flexible and workable of the building limes and is the key to its versatility.


Once slaked, lime putty is mixed with a range of aggregates to make a breathable mortar for bedding in stone, rendering, pointing and plastering buildings.

Remarkably, and unlike cement or gypsum which tend to trap or retain moisture, these mortars behave like a poultice, actively drawing moisture and harmful salts away from the fabric of the building and leaving it sound, dry and pleasant to Iive in.

When time eventually takes its toll this soft poultice can be replaced or repaired, leaving the brick or stone substrate dry and intact.


Diagram showing the lime cycle