The complete process of white washing can be carried out under the following operations.
Preparation of white wash
Preparation of surface
Application of white wash
Step-1 [Preparation of White Wash]
The white wash is prepared from fresh burnt shell lime or pure stone lime mixed with water. Shell lime is preferred to pure lime as it is whiter and slakes more perfectly to a smoother paste.
To prepare white wash, fresh lime is slaked at site of work and is dissolved in a tub with sufficient quantity of water.
After slaking, it is allowed to remain in the tub of water for two days and then stirred up with a pole until it attains the consistency of thin cream.
The mixture is then strained or screened through a clean coarse cloth.
Clean gum dissolved in hot water is then added at the rate of 2 kg/m3 of lime (or 4 kg/m3 of thin cream or white wash water) to the white wash water. The solution so formed is called as white wash.
To prevent the glare effect due to white wash, sometimes, the copper sulphate at the rate of 4 kg/m3 of thin cream is added. In order to have better adhesive properties, alum or common salt may be added in the same proportion as gum.
Step-2 [Preparation of Surface]
Before applying white wash to new wall surface, it is essential that surface should be cleaned, brushed and made free from loose materials and any other foreign matter.
If the surface to be coated is extra smooth or over smooth, then coats will not stick to it. In such a case, the surface should be rubbed with sand paper to ensure proper adhesion of white was.
In case of re white washing, all loose material and scales should be scrapped off. The old loose white wash is removed by rubbing with sand paper. All holes in wall, irregularities of surface, minor repairs, etc. are corrected in advance by filling with lime putty.
All greasy spots should be given a coat of a mixture of rice water and sand so that the finishing wash may stick to the surface. If old white wash is discoloured by smoke or other reasons as in kitchens, factories, restaurants, etc. then in such cases, the surfaces should be given a wash of a mixture of wood ashes and water or yellow earth, before the application of white wash.
Cement plastered walls should be washed with a weak solution of soap and dried before applying white wash.
Step-3 [Application of White Wash]
The white wash is applied to a specified number of coats with a jute brush. Usually, three coats are required for new works and for scrapped surfaces, while one or two coats are considered sufficient for old work.
For each coat, one stroke is given from the top downwards and the other from the bottom upwards over the first stroke, and similarly one stoke from the right and another from the left over the first brush before it dries. Each coat should be allowed to dry before applying the next coat.
The finished dry wash surface should not show any signs of cracking or peeling and should also not come off readily on finger when rubber.