Mix lime in water to get a sufficient consistency, watery just like paint so it can be easily applied using a brush. For old walls you need to make a thicker mix, for new walls make it more diluted because fresh walls will absorb more water, 3-4 coats should be good to go. Limewash makes a lot of difference in the water-resistive properties of the wall. It is a surakshakavach (safety shield) for the plaster. There is no measurement in preparation of mixes with lime, only intuition.
Salt is added to the whitewash, this greatly reduces the dusting of the whitewash. A little neel, that is used for washing clothes (in powder form) is tied in a cloth and stirred with a stick in the mix. This makes the colour bright, and the wall will look as good as new, even after 2-3 years. Before any function in the house, the boys of the house get some lime and neel and paint the home. These whitewashed walls are safed sada bahar, our lime is very seedhi sadhi (simple), just like our villagers.