MasterBuild Africa

The use of lime in construction

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Lime is a major constituent in exterior and interior stucco and plasters, enhancing the strength, durability, and work-ability of these finishes. It has been used as a primary ingredient in masonry mortars for centuries. This has continued to the present day in both historic and contemporary applications. Mortars made with lime and cement exhibit appropriate compressible strength, low water permeability and superior bond strength.

Most masonry produced before the 20th century used lime-sand mortar. The elasticity of high cement-lime mortars allows for expansion and contraction of historic masonry walls without causing damage. However, these walls which have low compressible strengths can be damaged by modern masonry products with higher strengths.

Studies have compared the performance of cement-lime mortars to that of masonry-cement mortars (which use limestone and other additives instead of hydrated lime) and mortar cements.  Cement-lime mortars have shown higher bond and shear strength, and lower water leakage.

Uses of Lime in Building Construction

Lime wash: Lime wash is a versatile, accommodating and robust surface  covering; compatible with a variety of building surfaces. It is easy to maintain and durable.

Site Preparation: Lime can be used to dry wet sites. It reacts with clay to provide a more stable base for building construction.

Hempcrete is a mixture of hemp hurds (shives) and lime(possibly inclusive of natural hydraulic lime sand or pozzolans) used as a material for construction

Autoclaved Aerated Concrete (AAC): Lime is also employed in the manufacture of innovative lightweight cellular concrete products, such as autoclaved aerated concrete (also called aircrete). This can be formed into blocks as well as large masonry units or insulation slabs.

Addition to concrete products: Hydrated lime can be added to concrete mix used to make blocks to produce a dense and water-resistant product with more precise edges and corners. This improves reflectivity and reduces loss through breakage.

Calcium Silicate Brick: Calcium silicate(sand-lime) brick is employed in standard masonry construction in the same manner as common clay brick.  Sand is mixed with high calcium lime (quick or hydrated) in a wet state, and then molded into bricks and autoclaved.  The lime reacts with silica to form complex hydro dicalcium silicates that bind the brick and provide high dimensional stability. Lime is also used to make hollow sand-lime building block, tile, slabs, and pipes.

Insulation Materials: Some insulating materials, molded as units, contain lime and diatomaceous earth or lime and silica. Here, lime serves as a binding agent, reacting chemically with the silica present in the mix to form calcium silicates.

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