Exterior painting can be more complicated than interior painting, as external factors often contribute to exterior painting. For example, rain is a significant factor in determining the success of exterior wall painting and can be detrimental to the job if not factored in. Hence, a professional home exterior painting contractor considers rain forecasts in his schedule and ensures the paint is dry before it the next rain. Regarding how long paint needs before it rains, it is best to let the paint dry at least twelve (12) hours before it rains. This gives the paint enough time to dry, preventing it from wiping off when it rains.