Taken from American Painting Contractor, July 2010. “Prime Investment” by Debbie Zimmer
If you purchase a top-quality 100 percent acrylic latex interior paint, you probably won’t need to spend time applying a primer to the wall surface. That’s because many of these paints act as both primer and paint.
However, in some circumstances, it may still be advisable to invest in a specialty primer as a first coat.
Specially formulated stain-blocking primers are made to protect the new coat of paint from “bleed through” of staining matter such as embedded dirt, grease, ink or crayon marks, rust, or smoke residue. If the walls are messy or marred even after cleaning them, you might want to consider applying this type of primer as a failsafe before you paint.
Another specialty primer that is useful in special circumstances is a “vapor barrier” primer. These undercoats are often applied in kitchens, bathrooms, laundry rooms and other areas that tend to be damp and humid. Their purpose is to minimize the passage of moisture of exterior paint. Vapor barrier primers also help maintain a comfortable level of indoor humidity in colder months.
Remember that all latex coatings – primers or paints – are much lower in odor than oil-based finishes, making them far more pleasant to work with and to live with indoors. Plus they are much kinder to the environment.