What Does Paint Primer Do, and When Is It Necessary?

What does paint primer do? Do you always need it? These are the questions that many DIYers run into when starting a new painting project, and they’re great ones to ask because primer can make a huge difference in how your project looks once you’re done. 

Giving a room a design makeover by freshening up the walls is a DIY that most people can tackle. Even so, that doesn’t mean you should dive straight into slapping on a few coats of paint. Proper paint prep work is the key to achieving a long-lasting, smooth finish. The pros often start a painting project by protecting and sealing the surface with a primer, which leads us back to our initial question: What does paint primer do? Well, long story short, it does a lot. 

What Is Primer?

Primer is an adhesive undercoat you apply to the walls before the paint of your choice. Without getting too scientific, wall paint has a high volume of durable, color-creating pigments, while primer has more resins. These resins create a strong chemical bond between the wall’s surface and the primer. Basically, primer sticks to your wall like glue and smooths the surface so that your wall looks flawless when you’re done painting.

Here are some of the top reasons you should always consider primer as the first step toward your room’s makeover: 

• Primer creates a smoother, more even surface.

• Primer seals the existing surface to stop it from absorbing your pricey paint during application.

• Stain inhibitors in primer prevent blotches and odors from seeping through to the surface.

• Primer prevents peeling paint by providing a stable surface for the paint to stick to.

When to Use Primer

Knowing what paint primer does can help you figure out when to use it. However, if you’re on a tight budget or are short on time, you might wonder how necessary a coat of primer really is. It pays not to skip this step in the following situations.

When Painting Over a Dark Shade

Trying to paint over navy blue walls with a neutral shade? Use a coat of primer to stop the darker shade from making an unwanted appearance. That way, you won’t have to apply so many coats of more costly paint.

In a Greasy Kitchen or Humid Bathroom

A hard-working kitchen will inevitably be subject to grease splatters, and mold stains or water spots can gather on the walls of steamy bathrooms. Even after you clean your walls for painting, these blotches can bleed through newly applied paint. Using a sealing, stain-inhibiting primer covers these contaminants for good.

On Certain Surface Types

Primer is especially important on surfaces that absorb paint or where the paint struggles to stick. These surfaces include:

• Porous surfaces: Things like newly installed drywall, brick, or bare wood trim typically need primer.

• Glossy surfaces: If you’re swapping from a semi-gloss to a satin, eggshell, or flat paint finish, applying a primer means the paint has a better surface to grab onto.

• Wallpaper: Primer stops wallpaper paste stains from peeking through and creates a surface that’s easier for paint to stick to.

• Metal or plastic surfaces: Adding a coat of primer to a rusty radiator or PVC trim prevents patchy, peeling paint. Sanding the surface first creates a rougher base for better bonding.

How Many Coats of Primer Should I Use?

You’ll be relieved to hear that one coat of primer should do the trick on most surfaces. But if you’re working with a surface that’s exceptionally porous, very dark in color, or has lots of stains, adding two coats of primer might be worth the effort for that flawless finish we keep mentioning. 

It’s never a bad idea to use more primer than you need, but not using enough can be detrimental to the final look of your space. If you’re not sure about using one or two coats for your specific project, err on the side of caution and use two. 

Which Type of Primer to Use

Just like when you’re picking out the best type of paint for your walls, there are different types of primer to consider based on the unique needs of your project. Primers are usually white, but tinted options are available, too. Explore the main types of primer below and which one to use to get the results you’ve been envisioning. 

Oil-Based

Good all-rounders, you can apply both latex and oil-based paints on top of oil-based primers. They bond well with most surfaces (perfect if you’re painting trim with a glossy finish) and are a favorite for sealing porous wood and stopping stains from seeping through on kitchen and bathroom walls.

Unfortunately, oil-based primers aren’t the most environmentally friendly option. They release harmful volatile organic compounds (VOCs) and require paint thinner for cleanup. Plus, you’ll have to be really patient if you use an oil-based primer, as they take longer to dry.

Water-Based

Water-based primers (also called latex primers) are available in no- or low-VOC formulas, making them a step up from oil-based primers in terms of eco-friendliness. Additionally, water primers are easy to clean up and apply, and the result is a lovely smooth surface on things like rough drywall. 

These quick-drying, flexible formulas work well on wood, which expands and contracts as temperatures change. However, they’re not the first choice for surfaces that are subject to stubborn stains (we’re looking at you, kitchen walls).

Shellac-Based

If you want to cover up stubborn stains from severe smoke or water damage, durable and quick-drying shellac-based primers are the ones to grab from the shelves. This type of primer contains a denatured alcohol solvent, which basically means that the primer quickly and easily seals in odors and stains. 

Shellac-based primers can soften when exposed to higher temperatures, so they do their best work spot-priming small patches of tough stains rather than covering an entire room.

When Can You Skip Using a Paint Primer?

If you pass on primer, you can still paint a room like a pro. Here are some times when you may be able to safely paint your space without that extra first step:

• When you’re painting on top of previously painted walls that are in good shape (i.e.,  smooth and stain-free)

• When the new paint shade is similar to the old one (or darker)

• When you’re using a high-quality self-priming paint

DIY vs. Hire a Pro 

With a bit of time and attention to detail, paint jobs around the home (including adding primer) are within reach of most DIYers. But if you're short on time or aren’t physically able to do the task, you might want to call in some local interior painters. The average cost to paint the interior of a house is roughly $2,000, but the final price will vary greatly depending on the type of paint you want and how big your project is. Budget for between $2.75 and $4.70 per square foot (including priming).

If you’re just worried your brush strokes won’t cut the mustard, you can always do the prep work (like tarping, taping off, and cleaning) yourself and hire a painter for the priming and painting, which could save you a little extra money. Regardless, professionals almost always use primer for their jobs to ensure you, the customer, have the best outcome possible.