skip to main page content :: Town & Regional Planning Home > Glossary Home > L >


- Any reference to lime usually means lime mortar. Lime is calcium carbonate, the main source of which is limestone. Lime mortar is produced in a process which basically involves, burning the limestone, then adding water to produce a base material to which various aggregates or additives are introduced depending on the end use of the material which can be anything from painting to building. The principal of lime mortar is that by a process of carbonization, the material reverts to calcium carbonate, which is stable, and depending on what has been added, solid.

Carbonation - the chemical reaction which takes place when slaked lime (calcium hydroxide) combines with the carbon dioxide present in the atmosphere and hardens to form calcium carbonate.
Coarse stuff - lime putty, well mixed with an aggregate to form a basic lime mortar, usually in the ratio 1:3.
Hydrated Lime- is produced when just enough water is added to quicklime to slake it, most lime is supplied bagged and powdered, in this form.
Hydraulic/non-hydraulic lime - a hydraulic lime produces a mortar with setting properties assisted by the presence of water; hence, hydraulic limes are sometimes referred to as "water limes". This set is caused by clay substances present within the original lime source, in effect a naturally occurring additive. Non-hydraulic limes are a purer substances which can only achieve a set through carbonation, and are therefor sometimes referred to as "air limes".
Knocking up - re-working lime mortar to a stage when it is suitable for use. It is seldom necessary to add water, and when it is added, it does not affect the quality of the mix, unlike remixing most modern mortars and plasters which have started to dry, where adding water is necessary and is generally perceived as bad practice.
Lime cycle - calcium carbonate (CaCO3) burnt in kiln at 880c+ = calcium oxide (CaO) add water = calcium hydroxide (Ca(OH)2) exposed to air, carbonation occurs = Calcium carbonate (CaCO3). (Illustration)
Lime putty - Ca(OH)2 calcium hydroxide, made from quick lime slaked in water, to form the soft buttery mixture which is lime putty.
Lime wash - in effect a very thin lime putty, used as a paint or protective coating, can contain a binder such as linseed oil or tallow. It is usually white, hence white wash, pigments were added to form a colour wash.
Quicklime - CaO, calcium oxide, a caustic material made from limestone which has been burned to drive off the carbon dioxide, remains very unstable until slaked.
Slaked lime - Ca (OH)2 calcium hydroxide made from quicklime, mixed or slaked with water. May be in form of putty or dry powder if slaked with a minimum of water.