What is Lime Used For in Construction?

February 22, 2024

Lime has been used to create hygienic surfaces and improve comfort conditions within buildings for thousands of years. It is caustic and has the ability to disinfect water. It is a very reactive material that reacts with carbon dioxide from the air to form calcium carbonate which gives it cementing properties. It is also a very effective binder for stone and brick masonry structures.

Lime is made by heating limestone (a sedimentary rock composed mainly of calcium carbonate) in a kiln to produce quicklime and then slaking it with water to form hydrated lime or ‘putty’ lime. The hydrated lime is reacted with aggregates and water to form mortar or plaster.

Its low embodied energy means that it has less impact on the environment than cement. Moreover, its porosity and permeable nature allows it to stabilise moisture levels within buildings by absorbing and releasing moisture which reduces surface condensation and mould growth.

There are 3 main types of lime used in construction: pure, hydraulic and slaked. Hydraulic lime is a powder like Portland cement and can be mixed with aggregates to make mortar or plaster. Slaked lime is a thicker paste which can be mixed with water to make putty or mixed with crushed rock and other materials to create concrete.

The different types of lime vary in their chemical and physical properties. Poor lime is not recommended for historical renovations. It is very slow to set, has weak bonding and a grey appearance. NHL 2 is a softer and slower setting lime for general building where conservation is the primary concern or with soft or deteriorating stones and bricks. It can be strengthened by adding pozzolanic materials which are minerals with high reactive silica. NHL 5 is a stronger and faster setting lime for use with hard materials that need to be more durable.

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