Lime has been used as a primary ingredient in masonry mortars for centuries, and this important use continues to the present day in both historic and contemporary applications. Mortars made with lime and cement exhibit superior workability balanced with appropriate compressive strength, as well as low water permeability and superior bond strength. Lime is a major constituent in exterior and interior stuccos and plasters, enhancing the strength, durability, and workability of these finishes. All of these lime applications are supported by ASTM specifications and standards. Papers and articles on a variety of building lime applications are available at www.buildinglime.org.
Type S (Special) hydrated lime is a fine, white, high purity product specially hydrated for convenient, trouble-free use in mortar applications. It is a uniquely American product, with much more stringent requirements for masonry performance than those imposed by any other country. Type SA (Special Air-Entrained) hydrated lime is similar, except that it includes an air entraining agent which produces minute voids in the mixed mortar. Either type will provide a superior quality mortar. Both are subject to the ASTM C207 Standard Specification for Hydrated Lime for Masonry Purposes.
Studies have compared the performance of cement-lime mortars to that of masonry cement mortars (which use limestone and other additives in lieu of hydrated lime) and mortar cements. Cement-lime mortars have shown higher bond and shear strength, and lower water leakage. For a more information on the use of hydrated lime for masonry purposes, click here. For a fact sheet on the use of lime-based mortars to create watertight walls, click here.
Most masonry produced before the turn of the 20th century used lime-sand mortar. The elasticity of high lime content mortars allows for expansion and contraction of such historic masonry walls without damaging the masonry units. These units can have low compressive strengths and can be damaged by modern masonry products with higher strengths.
Type S (Special) hydrated lime shows its versatility and beauty when used for interior and exterior plaster or render. ASTM C206 Standard Specification for Finishing Hydrated Lime requires that finishing lime be free of any chemical or physical characteristics that would cause flaws in the plaster.
Limewash is a versatile, accommodating, and robust surface covering compatible with a variety of building surfaces. It is maintainable, beautiful, stable, and long lasting. A copy of a paper on limewash presented at the 2005 International Building Lime Symposium is available here.
Lime can be used to dry wet sites. Lime can also react with clays in soil to provide a more stabile base for building construction. For more information on these uses, click here.
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”), which can be formed into block as well as large masonry units or insulation slabs. The 2005 International Building Lime Symposium included a paper on AAC.
Other Concrete Products
Hydrated lime can be added to concrete mix used to make block and other concrete products in order to produce a denser, more water-resistant product. By adding greater plasticity to the mix, lime also produces concrete products with more precise edges and corners, 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(di)calcium 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.
Some insulating materials, molded as units, contain lime and diatomaceous earth or lime and silica. In these products, lime serves as a binding agent, reacting chemically with the available silica present in the mix to form calcium silicates. The lime-silica reaction is also employed in making microporite insulation.