white paint being poured into a tray

Paint Primer, Sealer & Undercoat | A Complete Guide For Beginners

This complete guide will give you a better understanding of what paint primer, sealer, and undercoat are and when to use them in your next painting project.

When it comes to painting any surface in your home, the most important part is preparation. Before applying the final coat of paint, you will have to figure out if you will need to use an undercoat, primer, or sealer. Using the right product during a project will determine how the final painted surface will look after it dries. It also affects the longevity of the paint job.

To help clear up any confusion between each product, we have broken things down for beginners or people looking for a refresher on this topic.

What is a Paint Primer?

Paint primer is the first coat applied directly to any bare surface before the final coat of paint. Primers are in the painting process because they adhere, seal, and bond to any surface. This bond creates the perfect foundation for your final painting. Primers also serve as a protective layer that protects the surface from moisture. When used on steel primers prevents it from rusting.

What are the Types of Paint Primer?

Latex Primer

Latex primers are water-based, so they are low on VOC (Volatile Organic Compounds), which means they don’t have a strong smell. They are very flexible so, they help prevent wall cracks. Finally, they are fast-drying and easy to clean.

Oil Primer

Next, you have Oil Primers. They dry slower and can be a hassle to clean up. But they are great in blocking stains and tannins from bleeding through the topcoat. Oil paint primers are not as flexible. It can cause cracking when used on wood.

fresh start oil primer

Shellac-Based Primer

Finally, there are shellac-based primers or alcohol-based primers. Shellac-based primers are unique because they block both stains and smells. Like oil-based primers, Shellac-based primers also block tannins from bleeding through. Finally, shellac primers are fast drying and can be used with both water-based and oil products.

bin paint primer

What is a Sealer?

Before painting a surface, you should apply sealers. They provide fantastic adhesion and can be a substitute for paint primers. What makes sealers different is that they make porous surfaces non-porous. It also can be used before primers to create another protective barrier. Another advantage to using a sealer is that it can be used between opposing finishing coats. Ex: using latex paint over oil paint.

When to use a Sealer

If you are working on a surface that has already been painted you can use a sealer. The sealer seals in the existing layer of paint and creates a surface that is adhesive and will bind with the new layer of paint.


What is a Undercoat?

An undercoat is applied between the primer/sealer and the finishing coat of paint. It serves to create a stronger bond between the two layers. Its function includes providing a tough barrier to prevent water penetration and evening out rough surfaces. In most cases, after the undercoat is dry, you should lightly sand it till it’s even.

When to use a Undercoat

We will recommend using an undercoat if you will be working with enamel finishes or if you will be working on a surface that has already been primed or painted. After make sure you lightly sand the surface before the final coat.

undercoat paint

Common Questions About Paint Primers