When do I need to use a primer?
Often when I’m estimating projects, studious homeowners will ask me “Are you going to prime the walls?” Most of the time the response is “No, we don’t need to use one.”
Sometimes a feeling of doubt will be noticeable form their expression. I can almost hear them thinking to themselves. Does this guy know what he’s talking about? I thought you always prime before painting?
I’m not sure where all the misunderstandings about primers came from, but let’s dive in a bit into what different primers are supposed to do and when to use them.
Primers are chemically different from paint finishes. This is because they serve different purposes. I like to think of paint finish as a really nice tv with high resolution and fancy settings, but that can only accept one kind of cable, maybe an HDMI to connect to the television. Maybe you’re connecting to a computer, smartphone, or some other device that requires special connections and converters. Those converters and connectors are the primers in this analogy.
Most the research and development for paint finishes goes into the “front-end” of the product. Things like durability, shine, color ubiquity, ease of application, and leveling. Paint finishes are designed on the “back-end” to hold really well to a painted dry-wall surface (most likley the walls that are in your home). For insurance, it’s always a good idea to sand the walls a bit, giving them a “bite” for the paint to grab onto. Any situation that is more complicated than painted drywall will require a primer. Specific primers are made for specific conditions and substrates. We’ll look into a few examples here that should help you intuitively know what you’ll need, or at least give you the right place to start when researching what you’ll need.
One word we’ll be using in this article is “substrate.” The substrate is the construction material that the paint or primer is going onto. If we’re applying a primer to bare wood and then painting, we are applying a primer to a substrate (bare wood) and then painting over the primer. If we’re painting a wall in a house that is already painted, we are really just painting a wall, and the substrate is drywall. Sometimes we will apply directly to a substrate, sometimes we won’t. In painting, the substrate determines what kind of primer you’ll need to use, but conditions of those substrates can determine a different kind of primer. We’ll go over the 3 main families of primers below.
Oil-Primer – The exterior blocker
If you’re a homeowner with any part of your home made of wood, you should keep a gallon (or at least a quart) of oil primer in a climate controlled part of the house. If it freezes, it’s trash, and a pain to get rid of, so don’t buy it if you don’t have a place to keep it. Oil primer’s biggest utility at Sabatini Pro Painting comes from it’s relationship with wood. Unlike latex (water-based) primers, oil primer is absorbed into wood fibers and blocks tannins from coming to the surface. This creates a much stronger bond to the wood surface leading to longevity of paint finishes. Using the wrong primer, or no primer will cause the paint to flake pretty quickly, exposing the wood underneath. I see this everywhere and it’s a lot of work to clean up. Not using oil primer when you should is a very expensive mistake, and it’s usually evidence that whoever painted the substrate was either unaware of the need for oil primer or unwilling to use it. Oil primer is also used over interior walls that have had wallpaper removed. The primer will block any hidden residue remaining from the wallpaper glue and give you a safe surface to move forward with. You may be fine using a latex primer if oil primer is not a possibility, but you are exposing the project to some risk that residue will come through and make its way to the surface weeks or months down the road. Be aware – Oil primer has a very strong odor and will make you and those around you light headed without proper ventilation AND ventilators. As of the time of this writing, the proper ventilation masks sold by paint stores are very difficult to get a hold of. If you can’t obtain them, it’s better to ask a professional to handle this part of your job if oil primer is needed. Oil primer also dries pretty slow, meaning that it will continue to give off a strong odor for quite a while (4-8 hours). If you can, take it outside; and if you can’t, get everyone else (especially kids and pregnant women) outside. Oil primer cleans up with paint thinner.
Latex (water-based) Primer – The Interior swiss-army knife
We use latex primers mostly for new unpainted drywall, wall repairs, interior wood, and dark, deep colors like black, red, and dark blue. Our biggest use comes from wall repair. When we fix nicks and holes in the wall, remove auxiliary outlets and patch the hole, or do anything else that requires 1-5 coats of joint compound on the wall, we always prime over the repaired work before repainting the entire wall. It really makes a huge difference in “hiding” the repair work. By bringing the old wall and the new repair to the same level, it blends them together very nicely and very professionally.
You’ll also want to use a latex primer if you’re painting a wall to a very dark color, or painting RED. Red tints will require 5-6 coats to look right unless you prime the wall with a grey primer. If you’re concerned that the color you want to use may require a dark primer beneath it, call your local paint store and tell them your intended color. They will let you know if you need a primer or not.
For interior wood painting, an oil primer isn’t necessary because the paint finish isn’t battling the elements every second of every day. Because of that, a latex primer should be fine if the door is raw wood. If the door is stained, you’ll want to take it outside, sand it down, and use an oil primer on it. If that isn’t possible, you can test your luck with the latex primer and hope for the best. If you’re in this situation, the more sanding you can do the better. I would still recommend taking the door outside. If the door has a dark stain on it and it’s an old cherry or cedar, chances are low that latex will do the job and you’ll need to get yourself a stronger primer anyway.
Latex primer doesn’t smell like oil primer, and behaves similarly to regular paint finish.
For these reasons, I’d also recommend keeping a gallon of latex primer in the house as well, just in case you end up doing any wall repair in the future. Latex paint cleans up with water.
SHELLAC PRIMER – The big guns
Use of shellac is pretty rare, even for our professional painting company. On certain projects, like cabinet refinishing, it is a crucial part of our process. Other than that, we only use it to block certain stains that oil primer won’t cover. For substrates that have severe water or smoke damage, oil may not cover 100% of the problem area. In these situations, we’ll use shellac primer and move on with our project. Shellac is highly adhesive and will dry extremely quickly. Shellac also sands to a powder, making it the best primer to be used for cabinet refinishing projects. However, shellac is by far the stinkiest of all primers. Shellac is alcohol-based, and will make you feel SICK if you aren’t wearing a proper ventilator. Even with a ventilator, you’ll smell it immediately if your mask moves out of position even slightly. No one without a mask should be in the house while shellac is being used. Thankfully, shellac dry time is very fast, and as long as there isn’t an open container or paint tray of shellac lying around, the smell will dissipate quickly. Put it away as soon as you’re done with it and open all the windows nearby. I wouldn’t recommend keeping one of these in the house. It’s unlikely that you’ll run into a situation where you’ll need it. Shellac primer cleans up with denatured alcohol.
So those are your main primer families. There are several varieties of latex and oil based primers. Which one you’ll need depends on your specific project. A quick google search will tell you if your substrate requires a primer and which one you’ll need depending on the conditions. As long as you are using the correct family of primer, your project will go smoothly. Using the exact right product within that family will help you save additional dollars and time. For instance, there is a latex primer called PVA that is really only suitable for sealing new drywall. It’s inexpensive because it isn’t good for sealing wood or deep color changes. Well, if you’re priming an entire house of new drywall, there’s no reason to waste the money on a more advanced primer when all you need to do is seal drywall. You’ll be ok if you use that advanced primer, but you’ll be less efficient with your material budget. A few minutes of research could keep some extra dollars in your pocket. Of course, your local painting contractor should be aware of all these differences. Feel free to ask them questions about how they’ll approach the project and what materials they plan to use and why. Any competent painting contractor should be aware of these differences.
Best of luck on your exciting journey through the world of paint primers. May your finishes last forever.
Sabatini Pro Painting
There is also a synthetic shellac, but I find it to be pretty useless. If you need shellac, get the real thing.