In many cases, you’ll want to invest the time it takes to prime your surface before painting it with exterior paint. This is true in the following scenarios: Painting bare wood Using exterior paint on a slick surface, such as metal Applying paint of a different shade, or when covering stains When painting concrete or stucco You typically don’t need to use a primer before exterior paint if you are applying the same color over a previously painted surface or if there are no bare surfaces or stains you’re trying to cover.