The paint manufacturer will usually provide a technical guide for surface prep and application of the coating. Make sure you and your chang understand what is required and he follows through. 100% Acrylic usually provides the longest lasting water based coating, particularly where there are large surface temperature swings such as from direct sunlight. Surface prep, filling , and priming are key so that you get a good film that sticks to the existing surface coating. The technical guide will cover the details. If you know what the previous paint is, you may want to stay within that manufacturer’s formulations and type of coating.
Gloss or semigloss will usually provide the longest coating life and resistance to dirt sticking. Mildew can be an issue for latex paint. Many come with a mildicide already in the paint. If not, the manufacturer will have guidance for specific formulations to use. If you are spraying the paint rather than brushing or rolling, the manufacturer will specify if thinning is necessary and how much is allowed.
If the paint store employees are more sales oriented than technical, ask for the local manufacturer technical support rep contact information and discuss your application specifics.
