The ratio of paint to water for a mist coat on new plaster varies depending on the paint you are using. Here are some ratios suggested by different sources:

• 7 parts paint and 3 parts water
• 3 parts paint to 1 part water
• 70% water and 30% emulsion
• 50/50
• 10% water
• 2 litres water to 10 litres paint

Its important to note that the mist coat is effectively a watered-down emulsion, and the purpose of it is to seal the new plaster and help the top coat adhere better. The ratios above are just guidelines, and you should always check the instructions on your paint tin or consult with a professional if youre unsure. Its also recommended to use a non-vinyl water-based paint for the mist coat, and to stir the solution until you have an even consistency with no water sitting on top of the paint.