Types of Indian Plaster part 01
Speaking Natural Finishes series
If we draw insights from the composition of a human body and Natural Buildings, Plasters are the outermost skin of a building. They help to protect our buildings from various external entities like temperature and moisture (like the skin do). They impart an aesthetic language and dictates identity into a space as it is the outermost layer visible. The use of mud plasters maintains the breathing quality of the wall made of natural materials, enhancing the thermal comfort by keeping habitable temperatures inside. During summers, they remain cooler and during winters, warmth of mud can be experience.
The beauty of Indian plasters is that it utilises different natural derivatives from trees and herbs to increase the molecular strength, termite resistance and water repelling quality. Kitchen ingredients like Methi (fenugreek), Gur (jaggery), Kadukkai (Haritaki), Gooseberry, herbs like Aloe Vera, Cactus, Gums from Acacia (Arabic gum) and starch from rice, tapioca, wheat etc. are used. Animal derivatives like egg whites, animal hair, tallow, cow urine and cow dung are also crucial admixtures in plaster. Different types of mud and natural pigments like vegetable and mineral dyes helps in colouring walls through plasters. With the right recipe and simple preparation techniques, plasters can beautify the walls of any common man. The finishing layer can be of various textures depending on the technique used. Few exceptions like Thappi, Araish and Chettinad plasters requires skill and practice to execute and takes time to attain the elegant finish they offer.
Indian Plasters can be categorised into three for simple understanding.
- Mud Plaster
- Mud and Lime Plaster
- Herbal Lime Plaster
- Thappi and Araish Plaster
- Chettinad Plaster
Mud plaster constitutes of Mud and Admixtures. The particles within mud are Clay (finest), Silt and Sand (coarse). In pure mud plaster, constituents of mud itself act as binder (clay in mud) and aggregate (sand in mud). In-case of clayey soil or sandy soil, clay content of mud is preferably kept between 12%-30%, by mixing mud types in required proportion. Fibres like rice husk is added to reduce cracks. Cow dung is also added for better binding, anti-septic and water repelling quality. Admixtures of starch from tapioca, tamarind seed helps in better bonding of particles, bark and leaves of Neem and Teak, Turmeric keeps termites away, Gums derived from Kulamavu tree (Persea macrantha), Acacia tree (Arabic Gum) can reduce the dusting in plasters. Various colours can be attained with mixing different types of soil and natural pigments. At last, multiple coats of linseed oil, coconut oil or neem oil is applied to water-proof the surface.
Links to plaster methods:
Mud and Lime Plaster
Mud and Lime plaster constitutes of Lime, Mud and Admixtures. Lime is the binder here along with clay (in mud). Sand (in mud) in the primary aggregate. Fibres like rice husk is also added to balance the bonding within different components. Organic admixture like cow urine helps to boost bonding. Although lime keeps termites away, herbal termite repelling solutions will provide an extra protection in moist climatic conditions. Natural polymers and starch can also be added as per requirement to increase the stability of plaster after testing with different mud samples. Lime with time sets due to carbonation and makes a plaster layer as tough and solid as lime stone.
Herbal Lime Plaster
It consists of Lime, Surkhi and Admixtures. Lime is the binder here, Surkhi is the aggregate. Surkhi is burnt mud, derived from broken terracotta tiles or bricks or just burning mud lumps. Surkhi bonds well with Lime as moisture absorbed by the burnt mud facilitate settling of Lime. This is a major benefit of using Surkhi over river sand, which is facing shortage in availability due to heavy demand. Herbal mixes like Kadukkai-Jaggery mix initiates molasses reaction within and increase the bonding between particles. Natural Polymers derived from Cactus, Aloe Vera can enhance sticking of particles to each other.
This plaster shows resistance to erode with water splashing on it after settling of lime. Excellent water-proofing qualities makes it perfect for Water tanks and bathrooms.
Thappi and Araish Plaster
Thappi is the tool used for tapping or beating the lime after application to facilitate setting of lime. Thappi plaster technique is native to Rajasthan and other parts of India. The key ingredients are Lime (binder) and Surkhi (aggregate). Base layer of Surkhi and Lime is applied and Thappi is used to tap on the surface. This is repeating until you hear a ringing sound on tapping, after 3-4 days of Thappi in regular intervals. Cracks formed during drying get repaired in this Thappi process.
Above the first layer, wide range of finishes are possible.
- Lohi is the simple and quick finish, involving fine sieved Surkhi and Lime.
- Araish is the detailed and intricate finish, done in layer by layer. It uses marble dust, lime (slaked for long periods) and various natural pigments. It is applied with care and precision and is an art work mastered through practice.
Natural Gums and Polymers derived from Methi (fenugreek), Gur (jaggery) and Gguggul (Commiphora wightii) are used in various stages of plastering. This helps in attaining water-proof surfaces like Tadelakt plaster. This method gets rid of any fear of mud walls getting in contact with water. The procedure of applying plaster must be carried out with precise judgement maintaining work quality. Thannal has attempted to revive this technique through master mason Dawood ji’s work of Thappi Plaster on exposed walls and water tanks and initiated a workshop to help more people learn this and spread it.