Epoxy Primer Vs. Urethane Primer (Compared)

We all know that primer plays a critical role in promoting paint adhesion. It does so by creating a binding layer to which the paint will adhere.

Epoxy and urethane primers are two of the most popular types of primers. Even though both serve the same purpose, they are used in different situations.

A good example is that epoxy primer works best on bare metal, whereas urethane primer should be used as a surface primer on top of fillers.

If you are confused about which type of primer you should use, below, we will compare these two and help you make an informed decision.

epoxy primer vs urethane primer

What is Epoxy Primer?

Epoxy primer is what should go first over bare metal. This is a sealer that has a non-porous finish. Besides bare metal, epoxy primer can be used over fiberglass, wood, and plastic.

Epoxy primer is an excellent choice in auto paint applications since it is quite durable, offers exceptional adhesion, and can withstand high humidity levels.

Its non-porous finish and thickness allow the epoxy primer to prevent rust and corrosion on bare metal.

If you are painting your car, the above are all reasons why you should use an epoxy primer. It leaves a decent surface finish.

Therefore, you can use it on dents and cracks. That aside, you can use an epoxy primer to create the ideal undercoat for paint.

Car owners who are living in rust-prone areas should use epoxy primers. A two-part epoxy primer will prevent moisture from coming into contact with metal. As a result, rust won’t occur since critical ingredients will be missing.

Epoxy primers are cured with the help of a catalyst. Besides the auto industry, due to all the above features of epoxy primer, it is a popular choice in other sectors such as construction.

What is a Urethane Primer?

Urethane primers shouldn’t be used directly on bare metal unless you use specialized ones. These primers are well known for their hard finish. Unlike epoxy, they do not have robust rust prevention capabilities.

Therefore, before applying it, you need to rule out the presence of rust on the surface. To protect the metal from rust, you can use epoxy then urethane primer over it.

Urethane is a surface primer that should be applied after a sealer. This is what we were talking about in the paragraph above. Urethane primer can also be substituted as a filler primer. It will fill any dings and scratches, making it easier for you to sand over it.

With urethane primer, there is no limit to how much you can use it. Therefore, feel free to spray as many coats as you want, as long as you sand in between each coat.

Because it can be sanded repeatedly, the finish created by urethane primer is way smoother than that of epoxy primer.

How Are They Different?

  • Not Used on the Same Thing

Epoxy and urethane primers are not used on the same thing. One can be misled to think that they can be used interchangeably just because both are primers.

The epoxy primer should be used on sandblasted metal. As a result, it prevents rust and promotes maximum adhesion.

Urethane primer acts as a filler primer. It should be used once you are done with the bodywork. Epoxy is the basic primer between these two, and urethane is the surface primer.

Once you learn this key difference, it should be easy to know when and where you should use either product.

  • Epoxy Comes First, then Urethane Second

We all have varying paint techniques. However, if you have both epoxy and urethane primer, you should use the epoxy first. Epoxy will prevent rust while promoting better paint adhesion by acting as a sealer.

On the other hand, the urethane will fill in the dings and dents and create a harder finish on the surface. If you use both, you can adequately prepare the car surface for topcoats.

  • Epoxy Doesn’t Require Metal Preparation

Remember when we said that epoxy could be sprayed directly on bare metal? Well, it’s because it can work just fine without metal being prepared.

The same can’t be said for urethane paint. Without adequate metal preparation, such as a sealer, urethane primer won’t stick to the metal.

Even though epoxy sealer doesn’t need preparation, the metal should be cleaned before application. Don’t just spray directly.

  • Urethane Requires Thorough Sanding

Since after epoxy primer has been applied, fillers follow, there is usually no need to sand it. Since urethane primer goes to the surface, you must sand it before spraying a topcoat.

Failure to do that results in imperfections in the final finish. Therefore, do not forget to sand the urethane primer once you spray it.

  • Epoxy Leans Towards Rust Protection, and Urethane Primer Focuses More on Improving the Final Finish

Epoxy is a primer that goes underneath everything else. Its primary role is to protect the metal from rust. It also improves the adhesion of topcoats.

Urethane can’t be used for the same uses. It mostly leans towards improving the final finish of the vehicle and not protecting it from rust.

How Are They Similar?

  • They are Both Primers (Promote Paint Adhesion)

Even though they should be used in different situations, both epoxy and urethane are primers. Urethane and epoxy primer promote paint adhesion. They make it easier for topcoats to stick to the metal surface.

  • Can Be Used Together for a More Appealing Finish

When you use epoxy and urethane paint together, the results can be quite pleasant. The epoxy will act as the sealer and prevent rust.

Then the urethane will improve the finish by filling dents and scratches. When you apply a top coat, you will be pleased with the final finish.

It’s not a must to use both of them, but if they are available for use, don’t hesitate to spray the epoxy first and then urethane second.

  • Both Keep Impurities Away from Metal

Some might argue that only epoxy primer keeps impurities away from the metal. But do not underestimate the role played by urethane. Urethane primers create an additional layer of protection.

This layer makes it hard for oxygen and moisture to pass through until it reaches metal. When you combine both products, you are guaranteed maximum prevention against rust and corrosion.

  • They are Both Undercoats

Epoxy goes first, then urethane second. But at the end of it all, both are undercoats. As primers, these undercoats will keep the metal beneath safe from corrosion.

What’s Better about Epoxy Primer and Why?

By now, you should have understood the differences between these two. Before we wrap up, let’s look at what makes epoxy primer a better choice than urethane primer.

Epoxy guarantees rust protection. One of the things that make epoxy primer stand out is that it seals off the metal from moisture which causes rust.

Urethane primer has no capabilities. This, however, doesn’t mean it’s useless. Find out what makes it better in the sub-topic below.

What’s Better about Urethane Primer and Why?

Urethane primer is unique in its ways. It can be used as a filler primer. Do you have dents and scratches that require filling? Grab some urethane primer and spread it gently on the scratches.

Sand it afterward so that it leaves behind a smoother finish. With epoxy, you can’t use it as a filler. It only works as a sealer.

With the above in mind, it’s safe to say that they can’t be used interchangeably even though they are primers. Because with one, you will be risking corrosion, and with the other, you can compromise on the finish.

Who Should Use Epoxy Primer and Why?

Epoxy primer is ideal for car owners who have already sandblasted their vehicles and are only left with bare metal.

When you apply some epoxy primer, it should seal the metal from impurities such as water and air, which can lead to corrosion.

Other than protecting against corrosion, epoxy primer makes paint adhere easily to bare metal. That’s not the only situation where you can use an epoxy primer. You can use this primer on a mixed surface.

Also, you can use epoxy primer on other coatings or even as a final sealer because of its strong adhesive properties. The list of surfaces on which you can use epoxy primer is endless.

Who Should Use Urethane Primer and Why?

If you are only interested in improving the final finish or filling in dents and scratches, urethane primer is a great choice. Urethane primer works wonders when used on a sealer such as epoxy primer.

It fills in the dents that cause imperfections in the final finish. At the same time, when sanded down, it creates an excellent surface for paint adhesion.

Urethane primer is more common among detailers who are heavily invested in aesthetics. Unlike epoxy primer, which is a must-use in most painting jobs, it’s not a must for you to use urethane primer.

As an undercoat, urethane accentuates the colors of topcoats, thus ensuring your vehicle’s finish looks impressive.

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