In addition to priming bare wood, be sure to feather-in repairs so that surface differences don’t show through. Apply two coats to the entire area to lessen color variation.
Treat mildew on any type of siding with a solution of one part bleach to three parts water before you start painting. (Note: Always add water to the bucket first, then carefully pour in the bleach. And wear eye and skin protection and cover nearby plantings.) Leave the bleach-and-water solution on the siding for 20 minutes, then rinse thoroughly. Next, wash off mildew and any remaining dirt with a detergent solution. Let siding dry thoroughly; this can take a week or more if you power-washed it.
Though you can sand rough spots and fill gaps, cracked or split boards should be replaced, not repaired. Otherwise water can get in. Then the paint may crack as the damaged board expands and contracts or blister as water vapor tries to get out.
Deciding between shades? Considering changing colors? Paint a sample board with each color. That way you can see how each one looks before you paint, and you won’t regret your color choice.
Days with temperatures between 60 and 85 degrees and little or no wind are best. Try not to paint in direct sunlight, and never paint in the rain.
Transfer extra paint or stain into a glass jar, label it, and seal it tightly to prevent evaporation, which can affect quality, color, and consistency. Keep low-VOC paints out of the cold. Many areas will allow you dispose of latex paint with your trash if the paint has dried. Add a bit of cat litter to help dry the paint.