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White washing and colour washing of surfaces of building is necessary on both hygienic and aesthetic reasons. In order to obtain a clean, neat and uniform finish, it is necessary to adopt proper method for both preparation of surface to receive white wash or colour wash and for application of white wash or colour wash.
Preparation of White Wash
White wash is prepared from fat lime. The lime is slaked at the site and mixed and stirred with about five liters of water for 1 kg of unslaked lime to make a thin cream. This should be allowed to stand for a period of 24 hours, and then should be screened through a clean coarse cloth. One kg of gum is dissolved in hot water may also be added for every 10 kg of lime. Sometimes, rice is used in the place of gum. The application of sodium chloride (common salt) to lime-wash helps in quick carbonation of calcium hydroxide making the coating hard and rub-resistant. Small quantity of ultra-marine blue (up to 3 gm per kg of lime) may be added to the last two coats of white wash solution.
Preparation of Surface
The new surface should be thoroughly cleaned off all dirt, dust mortar drops and other foreign matter before white wash is to be applied. Old surfaces already white-washed or colour-washed should be broomed to remove all dust and dirt. All loose scales of lime wash and other foreign matter should be removed. Where heavy scaling has taken place, the entire surface should be scraped clean, any growth of moulds moss should be removed by scrapping with steel scraper and ammonical copper solution consisting of 15 gm of copper carbonate dissolved in 60 ml of liquor ammonia in 500 ml of water, should be applied to the surface and allowed to dry thoroughly before applying white or colour wash.
Application of White Wash
White wash is applied with moonj or other brush, to the specified number of coats (generally three). The operation in each coat should consist of a stroke of the brush given from top down-wards, another from the bottom upwards over the first before it dries. Each coat should be allowed to dry before the next coat is applied. The white washing on ceiling should be down prior to that on walls.
Colour Washing
Colour washing is prepared by adding colouring pigment to the screened white wash. Generally used pigments are yellow earth red ocher and blue vitriol. These are crushed to powder, before mixing. The colour wash is applied in the same fashion as the white wash. For colour washing on new surface, the first primary coat should be of white wash and the subsequent coats should be of colour wash.
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