Lime mortar is comprised of lime (hydraulic, or non hydraulic), water and an aggregate such as sand. Nowadays, it is generally used in conservation work or the construction of new buildings using traditional methods - generally for aesthetic reasons or as a planning requirement. 


There are 2 stages used to create lime mortar - carbonation and slaking:

Carbonation: Lime mortar is created by burning limestone or chalk with coal in process called carbonation. This forms calcium oxide - more commonly known as quicklime. During this process calcium dioxide is 'burnt-off', releasing itself as a gas whilst the end product (quicklime) clumps together to form lump lime.

Slaking: The quicklime is added to water, forming slaked lime (calcium hydroxide). It is then mixed with fine aggregates, such as sand or local aggrate to form mortars, render or plasters.


When lime mortar sets it slowly combines with carbon dioxide in the atmosphere to transform back into its original state - calcium carbonate. Traditionally, this could take months to set and meant a long delay before decorations could be applied. 

Hydraulic limes became more common by the end of the Victorian era. The introduction of hydraulic lime mortars considerably reduced the time needed to set, and also formed a much stronger bond. Hydraulic lime is created by the addition of silica - whether by addition of pozzolans (a range of siliceous or siliceous and aluminous materials) or by the use of clay that has a high silica content. A typical mix is 1 part hydraulic lime to 3 parts fine aggregate.


If you own a historic building, are looking to purchase historic building, or need any information on building conservation and restoration please contact us on 01342 833448.