The best tips for this section will come from your paint, so check the directions on the tin for the final word on paint performance and drying times under different conditions. In general, if it's wet and cold outside the paint inside will dry more slowly, while painting when it's excessively hot or dry can make the paint tricky to apply and may cause excessive brush marks and blistering.
If the air is warm and dry, paint will dry quicker and more consistently, so when painting indoors it's a good idea to turn up the heat in order to warm the air in the room you plan to paint. Push the warmer air in and cooler air out by running a fan from the air vent into the centre of the room.
Humidity also plays a crucial part in paint drying well, so it's also a good idea to keep humidity in the room low by continuing to run fans once you've finished painting, and even bringing in a dehumidifier if the paint is taking longer than three or four hours to dry.
Exterior walls will be colder to the touch than interior walls, so expect those to take the most time to dry. As long as the temperature of the room is maintained throughout the drying process, the paint should dry to the same standard quality on inside and outside walls.
In terms of outside air temperature, ideally the temperature should be in the suggested range for 48 hours after application otherwise the paint film may not form properly. This could result in problems including shorter paint life expectancy, mildew growth and adhesion troubles.
Extremely high temperatures may cause the paint to dry before it has had a chance to properly adhere to the surface, causing it to peel in the future.
It's also best to avoid painting in direct sunlight, especially during hot summer months as the heat from the sun's rays may cause the paint to dry too quickly. This can cause a number of problems including brush marks and inadequate adhesion.
After it's rained, you need to wait until the surface is dry before painting. Drying time is going to be different for different surfaces, as masonry and wood will absorb more moisture than a metal surface.