What are natural finishing plasters?
Natural plasters and finishes are eco-friendly. They are made mostly of materials directly available in nature and which require little or no energy for their processing. They are therefore more healthy. They can be categorised into two families: lime based finishes and clay based finishes. Lime and clay are both binders; and can be considered as the flesh of plasters; holding the rest of the materials together. Sand, stone dust, recycled building materials or natural fibres are mixed with them in different proportions to give a structure or a skeleton to the plaster.
The Components of a Natural Plaster
Clay is the smallest particle in the composition of soil which, when in contact with water, becomes malleable and can be mixed with other materials such as sand or fibres. It has an extremely high binding capacity. Clay based plasters naturally regulate humidity and temperature, they are very malleable and can be easily refinished if damaged. They will withstand splashes of water but cannot be exposed to running rainwater. They are very well suited for interior spaces.
Lime is obtained by firing limestone. It is a traditional material produced all around rural India and can be used as a replacement of cement to obtain waterproof plasters. Lime based finishes are also suitable for external walls as well as internal spaces that are humid, such as kitchens and bathrooms.
Stone dust is the replacement to river sand in traditional plasters. Unlike river sand that is mined from ecologically sensitive areas, stone/quarry dust is crushed and powdered granite chips, a byproduct of the stone mining industry. It is an aggregate within the plaster mix and provides it’s skeletal structure. The particle size of the stone dust can be graded and allows us to control the thickness and texture of the plasters.
Additives are numerous and can be added to the plasters to improve some of their properties such as making them more workable, more water resistant, making them stronger or changing their colour, etc. We use natural ochres and oxide pigments for colour. Natural soaps are used to improve workability and water resistance of the surface. Fibres are added to improve tensile strength and add a beautiful texture, The bio-polymers that result from the fibres also improve the workability and the water resistance of the plaster. Natural oils are applied as a surface coat to make the plasters water and stain resistant.