What Is Paint Primer? (& When To Use It?)

There are three layers of the painting process: a base coat (primer), paint, and a top coat (sealant). These three types of paints give a surface a colorful and durable finish. So, what is paint primer (base coat)? 

Paint primer (or base coat) seals cracks, holes, and imperfections in the surface. It also provides a smooth layer that the paint can stick to. Some types come with extra additives that block stains and moisture from bleeding through the paint. 

In comparison to paint, the primer has extra additives that help the coating stick better. That’s why it sticks on any surface, while paint doesn’t. 

What Does Paint Primer Do?

Primers help to improve adhesion, seal, block stains, prevent moisture, and guarantee a smooth result. However, some types come with extra additives and some don’t. For instance, a shellac-based primer will seal and block stains and moisture, while a normal primer doesn’t. 

Concrete primers are designed to soak into the concrete material and cover holes and cracks. While, self-etching primers corrode into the metal to increase the adhesion of the paint. So, the functions (or features) depend on the type. 

Here are a few features that all types have:

  1. Improved Adhesion – They help to improve the adhesion between the material and paint. They have extra additives that increase their adhesive qualities, so they will stick to surfaces that paint doesn’t. For slick surfaces, such as plastic or metal, you must apply 2 coats of primer so the paint has a smooth undercoat to stick to. This increases the adhesion between the paint and the slick surface. 
  2. Sealing – They will seal (or cover) holes, cracks, and dents in the surface. This prevents paint wastage because the holes are sealed (or filled), so paint is only applied over the primer coating. 
  3. Durability – Since paints stick better over a primer coating, this means the paint will last longer. That’s because the paint has penetrated the primer coating properly, so it’s harder for the paint to peel off. This means it increases the durability of the paint by providing a better surface to stick to. 
  4. Finish – The paint coating will be even and smooth if applied over a primer coating. That’s because the coating will provide a smooth and even coating for the paint to stick to. This leads to a high-quality paint finish. 
  5. Protection – Some types protect the paint underneath from moisture, water, and stains. 
  6. Switching Colors – They prevent bleed-through. When switching from a dark color shade to a light color shade (or vice versa), the primer will cover the old paint (dark or light) and prevent it from bleeding through the new paint. This allows you do add fewer paint coats to change the color of the finish. 

Is it Necessary?

In most cases, paint primer is necessary. You can still apply paint without it, but the adhesion of the paint will be weaker and the paint can peel off. However, if the surface to be painted is clean, smooth, and has no imperfections, then applying it isn’t necessary.

If the surface to be painted is cracked, wet, damaged, or not smooth and even, applying a primer before painting is necessary. That’s because it will cover (or seal) these imperfections from the surface, providing the paint with a smooth and even layer to stick to. 

Also, for non-porous surfaces priming is necessary before painting. That’s because non-porous surfaces don’t allow the paint to penetrate their surface and stick. But, the paint primer has extra additives that allow it to stick over a non-porous surface. So, you must apply 1-2 coats of it to a non-porous surface, allow it to dry, and then apply paint. This means the paint will stick over the primer coating, and not over the non-porous surface. 

However, if the surface is smooth, has no imperfections or bumps, and is clean, you can paint without a primer. 

Use Primer If:

Here are scenarios when you need to use paint primer before applying the paint:

  1. Switching Color Shades – Use it if you are switching color shades from a dark shade to a light shade (or vice versa). That’s because it will prevent the dark shade from bleeding through the light shade and affecting the finish. By using it, you can change the color shade of the finish with fewer coats. Use a grey-colored primer when switching the color shade of the paint. 
  2. Switching Paint Sheen – Use it between sheens if you are switching from paint sheens (from high-gloss to semi-gloss or matte), use a primer coating between the sheens.
  3. Fresh Material – Use it if you are painting a fresh material such as wood, concrete, plaster, or drywall. That’s because fresh materials are riddled with imperfections, patches, and moisture. So, two coats will prevent the moisture and patches from affecting the finish (or paint). 
  4. Stained Surfaces – If the material is stained, filthy, or greasy, apply a stain-blocking primer first. 
  5. Painting Wood Trim – Wood trims need a coat of primer for the paint to last longer. 
  6. Painting Slick Surfaces – Use it if you are painting slick surfaces. That’s because the paint won’t stick to a slick (or non-porous) surface without a primer.
  7. Porous Surface – If you are painting porous surfaces, such as wood, plaster, or drywall, you must apply a primer first. That’s because porous surfaces suck too much paint, so to prevent paint wastage, apply primer first. 
  8. Uneven Surfaces – When painting uneven or rough surfaces, apply a primer. If you don’t, the finish will have a rough or uneven coating.

Don’t Use It If:

Priming before painting is a good way to ensure a smooth and fine result regardless of the surface or texture of the material to be painted. However, here are a few scenarios when you don’t need a primer:

  1. The Surface is Perfect – If the surface is smooth, dry, clean, and even, you don’t need to apply it. This is because if the surface is perfect, there’s nothing to prevent the paint from sticking. 
  2. Using The Same Color Shade – If you are painting over old paint with the same color shade, you don’t need a basecoat. In such cases, light sanding with fine-grit sandpaper is all you need before applying paint. 
  3. Old Material – If you are painting over an old material that doesn’t need to have a smooth finish, you don’t need to apply a basecoat. However, the paint won’t last long. 

If You Paint Without a Primer:

In most cases, when you paint without a basecoat, the finish will not come out fine and smooth. Here are the other things that happen if you don’t use one:

1. Paint Adhesion Will Be Weak

Primer improves the adhesion between the paint and the material (surface). When you apply it, the paint sticks over it and not the surface. This improves the adhesion of the paint. 

But, if you don’t apply a base coat, the adhesion between the paint and the surface will be weak. If you apply paint over a non-porous surface without one, the paint won’t stick at all. 

2. The Finish Will Be Rough

If you paint without a primer, the finish will be uneven and rough. That’s because the imperfections on the surface aren’t sealed or hidden so they will show once the paint dries. However, if you apply a primer, it will cover or seal these imperfections and provide a smooth surface for the paint to stick to. 

3. Moisture Will Bleed-Through

If you don’t apply a primer before painting, the moisture on the material will bleed through and prevent the paint to stick or cause the finish to look stained. However, if you apply a stain-blocking primer, the moisture won’t affect the paint finish. 

Paint primer acts as a good stain-blocker and moisture-resistant film on the material. If you don’t prime a stained or wet surface before painting, the moisture and stains can easily bleed through the paint causing the finish to appear stained and blotted.

4. Cleaning Will Be Difficult

Without a primer, the paint won’t adhere properly to a surface. If you clean a paint coating that isn’t bonded perfectly to the surface, the paint can peel off while cleaning due to weak adhesion. 

5. Old Paint Can Bleed-through 

If you paint over old paint without applying a base coat, the old coating color shade can bleed through the new coating. For instance, if you apply light-colored paint over dark-colored paint, the old dark-colored paint can affect the light-colored paint. This is called bleed-through. 

However, a primer coating will prevent the old paint from bleeding-through. 

Priming Before Painting Wood

You must prime before painting wood because wood is a porous material that can suck too much paint. This can lead to paint wastage. However, a paint primer will cover the wood surface and prevent paint wastage. 

Also, wood is usually riddled with imperfections that can affect the finish qualities. So, before painting wood, apply a stain-blocking primer to allow the paint to stick properly. 

However, a primer coating will cover (hide) the wood grain color. So, if you want to apply a clear coat for the wood grain to show, don’t apply it. Also, you shouldn’t apply it to wood if you want to apply wood oil or sealant. 

Final Words

Priming before painting is necessary for most surfaces. Priming will cover imperfections, prevent paint wastage, and provide a smooth and even surface for the paint to stick to. Without a primer, the paint won’t stick to the surface properly and can peel off. 

However, you can paint without a primer if the surface is in a perfection condition. 

Tony Adams
Tony Adams

Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,

Leave a Comment