It's possible to paint over oil-based wood stain with latex paint if the painter prepares the surface properly. Painters need to remove as much stain as possible by sanding or scraping. Then, they need to clean the surface thoroughly, apply a primer and use high-quality latex paint.
Applying latex paint over an oil-based stain was once impossible. However, modern technology has allowed paint manufacturers to develop acrylic latex that adheres to virtually any surface, including plastic and oil-based finishes. However, it's best to sand the surface and use a primer to ensure optimal adhesion, especially if the surface is outdoors and exposed to the elements.
Before beginning the project, painters need to put on eye protection and rubber gloves. They should remove old, loose stain and wood fibers using coarse sandpaper for indoor projects and a hand scraper or a wire brush for outdoor locations. Painters also need to work with the grain to prevent unsightly scratches or scrapes. Next, they treat any mold or mildew with a 3-1 ratio of water and household bleach. They should leave the solution on for 20 minutes, applying more if it dries too quickly. After rinsing completely, the painters then clean all dust, dirt, wood chips, stain, and residual mold or mildew using household detergent and a sponge. They then apply a high-quality primer and paint the surface with an acrylic latex paint in a flat, semi-gloss or high-gloss sheen.