Lime Plaster

What Is Lime Plaster, When Used, Is It Still Used If So How Much

The exact definition of lime plaster has been clouded with misconceptions for some time now. People tend to misunderstand lime plaster for other types of plaster. So, before we move further let's get introduced to the real lime plaster!

Introduction to Lime Plaster

It's often thought that any mortar with lime as the main ingredient is lime plaster. However, that's incorrect. Such a mixture is usually referred to as ‘stucco,' ‘lime based stucco' among other things. And a mixture of calcium hydroxide (lime) and sand or any other inert filler as aggregate is known as lime plaster. When the lime in the lime plaster reacts with carbon dioxide present in the atmosphere, the resulting calcium carbonate, also known as lime stone, is formed leading to solidification of the wet mix. Furthermore, if aggregates such as sand are added to ‘hydrated' lime or ‘air lime,' a perfect lime plaster is formed!

However, if cement is added to lime, the change is not limited to just the physical appearance. It alters the chemical as well as mechanical properties such as durability, elasticity, porosity, and colour. Many-a-time, contractors add lime to cement in an attempt to lessen the effect of these properties.

Lime plaster has many uses. The most common is for frescoes that are created using colour pigments diluted with water and applied on a wet plastered surface.

Portland cement is not lime plaster, as is commonly misunderstood.

Advantages of Lime Plaster

Lime mortar has several important advantages over other types of mortars. In the current context, where in we are living in a world that's facing significant threat due to rapid industrialization, use of lime plaster can really prove to be beneficial. Some of the main advantages of lime mortar are elaborated below:

 

The lime plaster used in historic buildings (and many modern structures) had compressive strength of approximately 400psi. However, natural hydraulic lime with a compressive strength of between 800 to 1600 psi was lower than Portland cement's 3600 psi. Higher compressive strength leads to lesser flexibility. Since lime plaster has lower psi, it offers enhanced flexibility that is necessary a long life. Perhaps it is this quality that has ensured that many lime mortar structures have lasted for almost 10-20 decades!

However, because of the slow setting characteristic of lime plaster, it tends to remain soft for a long period of time (read months). Besides this lime is a very caustic material when mixed with water and calls for use of safety measures such as protective gear at all times.

Uses of Lime Plaster

Since lime putty is highly plastic, other mitigating materials have to be added to it to improve its plasticity and workability. Today gypsum plaster has replaced lime plaster as the preferred choice for interior base coat. Lime mortar is almost always used to give a finishing coat to interior surfaces.



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