A Primer on Primer: Why the Best "Primers" May Not Be Labeled as Such

If a paint creates better adhesion than a primer, which product is doing the priming?

For decades, the coatings industry has prioritized products labeled “primer,” often without fully addressing what priming is intended to accomplish. This misalignment between terminology and function has led to widespread confusion about product roles and performance. This article reevaluates the concept of priming—not as a product category, but as a surface function critical to system integrity.

Priming is not defined by a label. It is defined by what occurs at the interface between the substrate and the finish coat. Effective priming ensures surface sealing, uniform porosity, consistent absorption, and adhesion. When this foundation is compromised, all subsequent layers are vulnerable, regardless of their formulation or cost.

Traditionally, products like PPG Break-Through and Sherwin-Williams Emerald Urethane have demonstrated that superior bonding and surface control can be achieved with topcoats not marketed as primers. These coatings challenge the conventional paradigm, raising the fundamental question: If a paint provides better surface unification than a dedicated primer, which product is doing the priming?

Adhesion occurs through three mechanisms:

• Adsorption - (molecular surface attraction)

• Chemical bonding - (polymer-substrate interaction)

• Mechanical interlocking - (grip through surface texture)

The word “primer” on the label has no direct bearing on these interactions. Performance, rather than naming conventions, should be the standard by which substrate preparation products are evaluated. This requires independent, empirical testing.

The breakthrough came with nanotechnology. When Behr Ultra entered the market, it leveraged particles smaller than 100 nanometers. The physics are simple: smaller molecules penetrate deeper and bond more effectively. This translates to adhesion and superior sealing that traditional primers couldn't match.

One such test—the now well-known B Test—evaluated 32 drywall primers and revealed a consistent performance gap. In every instance, four coats of traditional primer failed to seal the drywall surface to the level achieved by a single coat of paint-and-primer-in-one. The difference was not in adhesion or coverage, but in film formation: specifically, as stated by the Vice President of Quality & Process Engineering at Behr Paint:

“The primary difference between the dried surface of the ‘B’ vs. the primers tested is film tightness—the optimized spacing between 100% acrylic polymer and pigments such as titanium dioxide.”

Figure 1. Surface view after application of four coats of drywall primer and one topcoat of eggshell paint. The “B,” originally brushed on with a self-priming acrylic paint, remains visibly distinct—highlighting the surrounding primer’s inability to seal the drywall and joint compound substrate. Despite multiple coats, the primer failed to unify surface porosity, resulting in sheen and absorption contrast.

This result underscores a broader reality: the most effective priming solution may not come from a can labeled “primer.” Performance defines priming, not packaging or marketing. The best-performing substrate interface product might be sitting on the paint shelf, not the primer aisle.

A recent case shared in a professional finishing forum highlights this disconnect between product labeling and real-world performance. A user applied primer to a door, followed by Sherwin-Williams Emerald Urethane Trim Enamel (EU)—a top-tier product known for its excellent adhesion. Despite priming and light sanding, the coating scratched off easily. The problem wasn’t the paint; it was the primer. In this case, the primer created a weaker link between the substrate and the enamel, effectively undermining Emerald’s performance.

This underscores the central point: the act of priming only improves a coating system when the primer itself contributes superior interface performance. If the primer provides less adhesion or weaker film formation than the paint it precedes, it becomes a liability, not a benefit. Evaluating products by label rather than function is a persistent flaw in both industry standards and retail guidance.

The “B” Test was initially published in June 2014. A downloadable version of the original article is available here. Also, an updated version here on this site.

The key takeaway here is not to prime unless your primer is doing something specific that your topcoat won’t achieve on its own.

Operational Leverage

The articles found here don’t just explain problems—they prevent them. These aren’t opinion pieces. They are field-validated protocols developed from real-world testing, experience, and industry field data. Every insight published translates directly to fewer callbacks, more accurate bids, stronger finishes, and less material waste.

That makes them loss prevention systems with profit gains, not just something to read. They carry real monetary value for painters, business owners, and even manufacturers who want to substantiate their claims that their products can back up.

FUN FACT: One of the popular primers on store shelves today is actually a paint with a primer label.