Paint and primer: What’s the difference and why does it matter?

paint rollers making green, red, orange, and blue stripes down a white wall
Photo by David Pisnoy on Unsplash

Oh, jeez, here we go again. The difference between primer and paint.

There’s so much misinformation circulating, it’s hard to determine who’s right and who’s wrong. Some say priming isn’t necessary. Some say there’s no difference, that primer is a kind of paint. (WRONG!) Some say you can use old paint as a primer. (Also WRONG!)

There absolutely is a difference between primer and paint. The ancient Egyptians knew it, the Italian Renaissance painters knew it, and now you’ll know it.

Paint and primer have different ingredients

Paint and primer were made for two different purposes. Of course they would contain different ingredients. You wouldn’t use silly putty in a Play-Doh Barber Shop, would you?

Silly Putty is far less pliable and would clog up the holes in your Barber Shop. Play-Doh is designed to be soft enough to push through those holes so you can cut it with plastic scissors into the worst mullet you can imagine.

Primer and paint are like silly putty and Play-Doh. They have different physical properties because they’re designed to accomplish different tasks.

What primer and paint are made of

There are a few differences in formulation, but some ingredients are the same.

Primer contains:

  • Resin. The “binder” that binds pigment particles to the dried film. In latex paint, the binder is usually vinyl acrylic, polyvinyl acrylic, or styrene acrylic. For our purposes, a binder is just a material that the pigment particles can “hang out” in until they get close together enough to crosslink.
  • Limestone. It’s not just an extender — it’s really a color-neutral way to add body and texture to the primer.
  • Titanium dioxide. An opaque, lightfast, and bright white pigment.
  • Additives. To handle things like frothing, clumping, and separating.
  • Vehicle. The fluid part of paint — solvent combined with resin. In latex paint, this would be water and vinyl acrylic.

Paint contains:

  • Pigment. The ingredient that gives paint its color. Pigments are mined or manufactured, processed, and ground to extremely fine particles before being added to paint.
  • May or may not contain titanium dioxide. TiO2 is a white pigment and an opacifier, meaning it’s very opaque and mixes with other pigments in a way that increases their opacity.
  • Vehicle

Paints don’t contain limestone. They don’t need to because they aren’t meant to provide body or texture on their own.

Whether or not they contain titanium dioxide (PW 6) depends on how light or opaque they are, or what pigments are necessary to mix the color.

Paint and primer are made for different purposes

Paint was invented thousands of years before primer. Paint used in caves definitely predates 11th century Egyptians and 14th century Italian Renaissance artists.

So, if people have been painting surfaces for thousands of years, why was gesso invented in the first place? Weren’t painters getting along just fine without it?

Gesso was — and still is — the primer used by oil painters to prime their canvases, wood panels, and other substrates before painting.

The primers you use to prepare your walls before you paint serves the same purpose. To seal the surface you’re painting to prevent over-absorption of the more expensive pigmented paint you’re painting with.

Do I really need to prime before I paint?

I don’t know.

Do you want to:

  • Spend too much time and money on paint because it soaks into the wall and requires two or three additional coats?
  • Over-spend on paint because it takes several coats to cover stains?
  • Throw your cash away to repaint because the color you applied never formed a stain-resistant finish?

Then painting without priming first is for you.

But if you have better things to do and spend your hard-earned scratch on, here’s why you should prime first.

Yes, you need to prime before you paint!

Sometimes the easiest of what you hear is wrong.

If you paint without priming first, woe befalls you:

  • You’ll throw away good money after bad by repeating this step too many times. Primer is made to seal an overly-absorbant ground (like drywall) so that you don’t waste paint on it.
  • Your paint job will be compromised long before you’re ready to paint again. You don’t want to spend all that time taping and painting, and now you have to do it again a few years later because the paint is peeling.
  • Forget about covering stains. They’ll show up again. Especially if anyone in your household has an affinity for Sharpies or spaghetti sauce.

Priming first guarantees you the best coverage and the ideal ground to accept paint layers. The paint you apply will adhere well to a primer. It has plenty of texture to adhere to.

That’s a no-brainer, isn’t it?

Important: If you’re using latex paint, apply a latex primer first. Applying latex over an oil-based primer will cause the paint to peel.

What about paint and primer in one?

Paint and primer in one is fine if you’re painting over a similar paint color. Usually.

Not useful for first-time paint applications. If you’re looking at raw drywall or wood, forget it.

Remember that any porous surface will absorb too much water from the paint and ask yourself if an opacifier will stop this. It won’t. That’s not the function of an opacifier.

Painting and priming serve different purposes and are formulated accordingly.

Takeaways

  1. Prime before you paint.
  2. Use a latex primer under latex paint.
  3. That’s it.
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