Primers are not always necessary in every painting project. To know when you should use a primer you first have to understand what types of primers are available and what they're intended to be used for. The best way to understand their intended uses is to first look at them by primer categories.
New/bare drywall is extremely porous and soaks up paint like a sponge and causes it to cover better in some areas than others; especially when you’re comparing drywall mud joints to the surrounding areas. Porous surfaces like drywall mud will cause visible differences in the final sheen of your paint called “flashing”.
To help achieve a consistent appearance with your final coat, when painting new drywall or over drywall patches it is always a good idea to first use a primer – and besides, using a quality drywall primer is typically much less expensive per gallon than using multiple coats of a quality interior latex paint.
Bare wood is among the more difficult substrates for a paint topcoat to adhere to. In the past, there was no substitute for a good slow-drying oil-based primer on bare wood. It takes a long time to dry, allowing plenty of time for it to soak into the wood, and it sticks better than any other type of primer to wood.
Even though old-fashioned oil primer is still the best for this use, nobody likes to wait 24 hours for a primer to dry before they can topcoat it. So the paint manufacturers have developed new, faster-drying technology in both oil and latex-based products that dry quickly yet still aid in the proper adhesion of your paint topcoat.
If you don’t mind waiting for the slow dry time and don’t mind the hassle of working with solvent clean-up products, we would always recommend oil based wood primer. If you don’t want those hassles but have to paint bare wood, it is still worth the time to use a quality latex wood primer before applying your finish coats.
There are several reasons why it is a good idea to apply a masonry primer before paint.
Some masonry surfaces can have a high pH level which will cause adhesion problems if you apply paint directly to the surface. A quality masonry primer will allow you to safely paint over a wider range of pH levels without risk of adhesion loss.
Another problem is called efflorescence; which are unsightly white, crystalline deposits that can form on any masonry surface. Many masonry primers are efflorescent-resistant and do a great job of keeping it from becoming a problem.
There are different types of stain-blocking primers for specific uses, but some of the more common situations where their use is necessary are: keeping water and smoke stains/damage from bleeding through the finish coat; painting over top of crayon, marker, or grease; and making a dramatic color change – especially when painting a lighter color over a much darker color.
Some surfaces are especially “slick” and pose a unique challenge for even the best primers when trying to get a coating to stick to them. Some examples would be factory coated metal sidings, ceramic tile, glazed block, plastic and vinyl shutters, and surfaces with a high gloss finish.
If you choose the correct bonding primer for your application you will be far more likely to get great adhesion of your finish coat to the surface.
There are a couple of exceptions to these categories:
- Multi-Purpose Primers have become very popular because of their universal application for a wide-variety of uses. A word of caution – some manufacturers have a tendency to oversell these products for situations that they are not necessarily a good fit for.
Before you grab a multi-purpose primer off of the shelf make sure that it specifically states on the label that it can be used for your intended purpose. When buying a multi-purpose primer go with a proven name brand such as Zinsser, Sherwin-Williams, PPG, or Glidden products.
- Paint & Primer In One products are one of the newest and most-popular trends in the industry. What a great idea! Who wouldn’t want to make their painting project easier by using a product that primes while it paints?
While this concept is wonderful in theory, it has limited applications when it comes to actually holding up well to the test of time. Again, a good rule of thumb is to stick to the highest-quality manufacturers if you decide to use one of these products, and make sure you check the label to ensure it can be used for your intended application.
For exterior new wood applications, one of our favorites is Duration® by Sherwin-Williams.
As a general rule for interior wall painting - especially over new drywall or drywall patches - we consider these “primer-in-the-paint” products to be a total marketing gimmick. We would advise people to not think of these products as something that will save you a coat of primer, but instead think of them as an opportunity to use an additional coat of the same material instead of switching products between the base coat and the finish coats. On new drywall, you will use 3 coats of the finish material instead of a primer coat plus 2 coats of finish.
Most projects where you’re going over a previously-painted surface do not require the use of a primer. In many cases all you’ll need to do is spot-prime any bare areas that need to be addressed before applying your finish.
If you’re coating over any surfaces that have never been painted before, just follow the guide above to find the proper category of primer for your project and you can’t go wrong.
If you're in the Greater Pittsburgh or Tampa Bay Areas and you need help with your priming and painting project, please contact us for a free consultation and quote!