What Is Primer Paint?

It’s often said a paint project is 90% prep and 10% painting. Consider applying primer an important part of the prep, because it can be critical to the overall results.

I once opted to skip primer when painting a desk, hoping to save time and money. This hasty decision turned my DIY project into a time-consuming mess, because the once-fresh coat of paint soon began to chip and peel.

Don’t make the same mistake. Learn, as I did, from industry pros Jeff Thorman of Home RenoVision DIY and Rachel Otto of Fleury Lumber. They told me all about primer paint, when to use it, and what can happen if you don’t.

About the Experts

Jeff Thorman,the host of Home RenoVision DIY, has 25 years experience as a contractor. Painting is his favorite home renovation task. With his tutorials on YouTube, he aims to teach and empower homeowners to renovate and remodel their homes.

Rachel Otto is the paint department manager at Fleury Lumber in Easthampton, Massachusetts, specializing in Benjamin Moore products. She has 10 years of industry experience.

What Is Primer Paint?

Primer paint is a coating applied to a surface before the actual paint. It’s formulated to stick to surfaces, seal porous materials or block stains. Some primers do all three, while others do one task better than another.

“A primer essentially [prepares] the wall to receive the paint,” Otto says. “There are acrylic [water-based], alkyd [oil-based] and shellac-based primers.”

While technically a paint, primer and paint are not interchangeable. “Primer is not as durable or attractive as paint, and paint does not have the adhesion and stain-blocking properties of primer,” Otto says. This comes down to each product’s chemistry.

Primer contains resins that penetrate and adhere to a surface to grip, seal and/or block stains. Paint also contains resins, but includes pigments for color and additives for durability as well. Pigments and additives also create paint’s thicker consistency and higher cost.

“Primer is cheaper to manufacture, because there are no pigments added,” Otto says.

What Is Primer Paint Used For?

Primer paint does three things:

• Seals porous surfaces: Primer resins seal new drywall, plaster or unpainted masonry (brick, concrete, stucco) to create a nonporous surface for paint. “Primer seals and primes the [surface] so it doesn’t suck up all your paint,” Thorman says.
• Adheres to the surface: Primer resins penetrate and interlock with the existing surface to create a solid bond.
• Blocks stains or existing paint colors: A stain-blocking primer under paint prevents stains from smoke, water damage or life in general. It also allows drastic color changes. “When changing from a dark or bright color to a neutral color, primer will help hide the older paint color,” Thorman says.

Do You Need To Prime Before Painting?

It depends. Always use primer when painting bare or previously unpainted surfaces. This includes new drywall or plaster, as well as bare metal, wood or masonry.

If painting cedar, redwood or knotty pine, prime first as well. Each contains tannins or sap that will seep through the paint surface if it’s not sealed first.

Before painting, prime any bare spots left from scraping and sanding during surface prep. Also, make sure to prime over any surface stains to prevent bleed-through, especially water and smoke stains.

It’s a good idea to prime before an extreme paint color change, too. However, previously painted surfaces may not require a primer coat before repainting. This is true if you’re repainting with the same or similar color, and if the existing coating is sound without peeling or chipping.

What Happens if You Don’t Prime Before Painting?

Three things, all of them bad.

Paint failure

Failing to prime bare or new surfaces can lead to chipping or peeling paint. It may last awhile, but will fail sooner than paint applied over primer.

Uneven paint color

Skipping primer before a drastic paint color change can result in splotchy coverage that will require more coats. “If you’re going from a red room to a white room, use a stain blocking primer so the red doesn’t show through,” Otto says.

Stain bleed-through

Paint is not formulated to block stains. If you don’t prime, no matter how many coats you apply, most stains will still be visible. “Even if you fix your leaky roof, the water stains on your ceiling will continue to show through paint unless sealed with a primer,” Otto says.

Unprimed wood that contains tannins will also bleed through paint.

Benefits of Priming Before Painting

Primer can lead to longer-lasting, better-looking results. It also can save money and time. “You use less paint overall, especially on porous surfaces,” Otto says, “and it helps your color stay true longer.”

How To Use Primer Paint

Primer paint is best used as a preparatory coating before paint to smooth the surface, create great adhesion and block stains. It is not meant as a finish topcoat.

How To Apply Primer Paint

Primer paint can be applied with a brush, roller or sprayer. “It goes on pretty much the same way as paint, but it’s thinner, so you’ll want less of it on your brush or roller to avoid drips,” Otto says.

She also recommends applying an even coat, because uneven coverage can show through the paint.

Priming Over Old Paint

Priming first can save money and time. “Primer is a lot cheaper than finish paint,” Thorman says. “In situations where you are going from a dark or bright color, a transition primer will save you money instead of extra coats of paint for coverage.”

If the old coating features some chipping or peeling paint, scrape these areas, then prime any bare spots. Once the primer dries, paint the entire surface.

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