Stains and odors. If you are faced with stains that show through the surface regardless of the amount of primer or the number of coats you apply or need to fight the cigarette smoke that stays locked in the substrate, you need a stain-blocking primer. You can purchase either an oil-based or water-based primer. Choose oil-based primer if you need to get rid of rust, smoke, wood tannins and water. Get water-based product to make cleaning easy and avoid unpleasant odor. They are perfect for solvent-based stains such as grease, ink and crayons. Stain-blocking primers are white and will need to be tinted if you are planning to use dark paint.
High-moisture areas. If you are looking for the best products for the areas that are high in moisture and prone to mildew such as bathrooms, kitchens and laundry rooms, you need a vapor barrier sealer. Humidity is one of the worst paint enemies since it causes peeling, flaking and blistering. Vapor barrier seal will seal the surface and will not allow most of the moisture to go through. If you are also faced with mildew, you'll need a stain-blocking primer followed by a special mildew-reducing topcoat (it will be marked as such). All existing mildew must be removed before painting.
Previously painted wood. If you are faced with previously painted interior wood such as doors and the paint is chipping or flaking, you will need to purchase an oil-based undercoat. It will do a perfect job attaching to the previously painted wooden surfaces and staying smooth in the process. Fast drying primers and sealers will soon become brittle. Oil-based primers will take about 2 days to dry but will produce a good result. If you still wish to opt for a water-based primer, look for acrylic-latex undercoat that can be sanded.
Color switch. If you need to follow through with a drastic color change (from very light to very dark or the other way around), you will need too many paint coats to do it. Choose a primer that can be tinted with lighter and darker colors in order to reduce the number of coats that will need to be applied. Tinting a primer gray helps the color become richer and help hide surface imperfections.
Exterior surfaces. Exterior surfaces always need special care since they are exposed to different weather conditions, including extreme temperatures and precipitation. The paint on the exterior surfaces will last longer if a good primer is used. The best choice will be the highest quality acrylic-latex primer for exterior surfaces. The label should read “100% acrylic.” If the primer is well-chosen you can extend the life of paint by several years.
Drywall (new or patched). The products that are used for the drywall seams react differently to the paint than the rest of the surface does. The difference between the surfaces can lead to flashing and improper sheen. In order to paint the drywall, you can use a drywall sealer. Standard drywall sealer is good for perfectly smooth surfaces. If there are some imperfections, you should go for a high-build drywall sealer which can be more expensive. However, it will do a better job making the surfaces leveled-out.