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Last edited 09 Apr 2023

Chettinad egg plaster

Chettinad plaster is a traditional technique of lime plastering that originates from Chettinad, Tamil Nadu in Southern India. It can be found on many of the mansions in the area built around the 1700's by the wealthy trading community known as Nattukottai Chettiars, and is notable for its particularly smooth light finish. It is created by using a specific local traditional plastering technique known as Chettinad egg plaster, a gradual process of applying 6 different thin layers of plaster with the first with sand and the last with the addition of egg white.

Base coat; the first layer or base coat of this plastering technique contains limestone, which is a hydraulic lime crushed and powdered, this is then simply mixed with sand and water to create a binding layer which is then applied to the existing wall to bond the new plaster.

Subsequent layers; four further layers are applied which are made of a mixture of shell lime (which is made traditionally), mixed with local Kalmavu white stone which is ground to a fine powder. The shell lime is made according to traditional hand methods, the limestone or sea shells (conches) are burned at high temperature, then water is added, which is known as slaking the lime. The sea shells are effectively calcium carbonate, which when heated up expels the carbon dioxide and becomes calcium oxide, when water is added the hot mixture steams and cools releasing the heat to create a crumbling mixture, which when dry is a white powder, this is which calcium hydroxide, lime plaster. The plaster is gradually applied thinner and thinner with each coat at this stage until ready for the final coat.

Final coat in the final layer the same mixture is created as before, but at this stage egg white is added to the mixture. First the egg white is agitated to create a soapy foam, and is then added to the lime plaster mixture, the egg white helps lighten the mix making it soft and helping to reduce shrinkage and potential future cracking. At this stage milk whey is also added, this is the liquid remaining once the more solid milk curd squeezed. As with any activated lime plaster the inactive original material is converted to a chemically active material during application and once applied, over time returns back to being an inactive material. As the mixed and applied lime plaster on the wall stays in contact with the air around, it re-absorbs the Carbon Dioxide in the space, in doing so, and over a longer period gradually returns to being a relatively hard calcium carbonate as it was in the form of the original stone and shells. During the final mixing stage pigments may also be added to the mixture and in some cases also vajjram (tallow) may be added.

The final stage might also involve rubbing the surface with stone to help in creating the fine smooth finish, closing or sealing the final surface thus requiring no further treatment.

A similar mixing method called Argamasa can also be found in the Phillipines from the period of the Spanish occupation, where egg whites were used as emulsifiers for lime renders. So much so that a culinary historian from the Phillipines Pia Lim-Castillo, noted that some time after the Spanish had arrived local cookies called San Nicolas cookies were made, most probably because of the remaining egg yolks left from the construction of the churches. “The extensive use of egg white and eggshells brought about the ingenuity of the Filipino women who saw all these egg yolks being thrown in the river,” writes Lim-Castillo. “Recipes were created to make use of the egg yolks, like pan de San Nicolas, yema, tocino del cielo, leche flan, pastries, and tortas.”.. “the number of eggs used ran into the millions.” (Eggs in Cookery, proceedings of the Oxford symposium on food and cookery edited by Richard Hoskin Prospect Books 2007)