Can I Apply Polyurethane Over Enamel Paint?

I’m guessing you just finished a surface with enamel paint and you want to seal the enamel with polyurethane. But you are wondering- can you use Polyurethane over enamel paint?

Polyurethane can be used over enamel paint to provide a very strong and vibrant finish. Polyurethane when used on enamel makes the paint coating resistant to factors that can ruin it like moisture and scratches.

The enamel paint is also given a glossy sheen that makes the enamel color vibrant or bright.

But that’s not all. What type of polyurethane should you use with enamel? And how do you apply polyurethane over enamel? This post reveals more so let’s go deeper.

Tip: Keep your eyes peeled for helpful tips in this article. See, you got one already. Let’s get to it.

What Type of Polyurethane Should You Use over Enamel Paint?

The best type of polyurethane to use over enamel paint is oil-based polyurethane. This is because oil-based polyurethane hosts the most benefits for enamel paints. Oil-based polyurethane is thicker, stronger, and will generally last longer on enamel paint.

Water-based polyurethane will also work on enamel but is best reserved for water-based enamel paints.

Tip: Never apply water-based polyurethane over oil-based enamel paint.

The polyurethane will not bond properly. This is because oil-based enamel when dry forms a glossy film that doesn’t allow water-based paints to stick properly.

Now, let’s find out how to apply polyurethane over enamel paint.

How To Apply Polyurethane Over Enamel Paint (Made Easy)

Applying polyurethane over enamel paint isn’t difficult. But the task can be time-consuming due to the level of prep work and paint application required.

To apply polyurethane over enamel paint, you’ll need the following tools:

  • Tack Cloth or Rags
  • Fine-Grit Sandpaper
  • Bristled Paintbrush
  • Razor Blade
  • Drop Sheet
  • Polishing Compound (Optional)
  • Hair Dryer (optional)

Here is a quick rundown of how to apply polyurethane over enamel paint:

  1. Prepare The Workspace
  2. Wipe The Enamel Paint
  3. Scuff The Enamel Paint
  4. Apply The First Two Coats of Polyurethane
  5. Apply The Final Coat of Polyurethane
  6. Apply a Polishing Compound

Now, let’s get to work.

1. Prepare The Workspace

Prepare The Workspace

The first step is to prep your workspace. Applying polyurethane over enamel can get messy. So you should prepare your workspace to handle that mess unless you want to spend the next few hours after painting on clean-up duty.

Put a large drop sheet on the floor to protect it from paint splatters. All objects and furniture on or around the enamel painted surface should be removed or covered.

2. Wipe The Enamel Paint

Wipe The Enamel Paint

The next step is to wipe the enamel paint with a rag or tack cloth. This is to remove any grime, sand grain, or debris on the enamel paint. All of these will prevent the polyurethane from sitting well on the enamel.

So they should be wiped off first.

3. Sand The Enamel Paint

Sand The Enamel Paint

After cleaning the enamel, you should sand lightly to scuff it. Doing this further helps to remove imperfections like paint pimples and bumps in the enamel paint.

Sanding also helps to remove the top glossy layer of the enamel paint especially oil-based enamel.

Not just that. Sanding lightly also helps to smoothen the enamel paint. For the polyurethane to be applied smoothly, the enamel undercoating has to be smooth too.

When you are done sanding, dust the enamel paint to get rid of sanded dust. Then you should…

4. Apply The First Two Coats of Polyurethane

Apply The First Two Coats of Polyurethane

Usually, you need just 3 coats of polyurethane to seal enamel paint. But the three coats can’t be applied all at once. This will make the finish amateurish. So, apply the first coating first on the sanded enamel.

After applying the first coat, wait till it dries. Usually, oil-based polyurethane coating dries enough for a recoat in about 12-24 hours. Water-based polyurethane dry enough for a recoat in about 4-6 hours.

When the first coating has dried, sand lightly with very fine sandpaper. The purpose of sanding between coats of polyurethane is to remove dust nibs that landed on the coating while it was drying.

Sanding also helps to improve inter-cot adhesion between successive coats of polyurethane.

When the first coat is sanded, apply the second coat and wait till it dries too. Then do what you did with the first coat, sand the second coating too.

Don’t sand Polyurethane with coarse or medium-grit sandpaper. These grits are too harsh for the polyurethane and will remove the entire coating.

5. Apply The Final Coat of Polyurethane

Apply The Final Coat of Polyurethane

The 3rd and final coat of polyurethane should be applied as smoothly as possible.

Apply the final coat of polyurethane in long brush strokes. Don’t move the paintbrush back and forth. Doing this increases the chances of brush strokes after the final coat dries.

After applying the 3rd coat of polyurethane on the enamel, leave it to cure. This will take several days.

When the 3rd coat has cured, you should…

6. Apply a Polishing Compound

Apply a Polishing Compound

This step is optional. Without a polishing compound, polyurethane will still seal enamel paint perfectly. But if you are looking for a high gloss finish or extra protection on the polyurethane, you can use a polishing compound.

When you have completed all these steps, you have successfully applied polyurethane over enamel paint.

Can You Mix Polyurethane With Enamel Paint?

You can mix polyurethane with enamel paint for a strong and moisture-resistant finish. However, you should only mix water-based or acrylic enamel with water-based polyurethane.

It’s not a good idea to mix oil-based enamel with either oil-based polyurethane or water-based polyurethane. Doing this will just ruin both the polyurethane and the enamel paint.

Mixing paint types is very common but when it comes to polyurethane, it’s not usually a good idea to mix with any other paint. Oil-based polyurethane especially should never be mixed with enamel either water-based or oil-based.

This is because oil-based polyurethane dries and forms a thick finish through a very different chemical process than enamel products. So mixing oil-based polyurethane with either oil-based or water-based enamel will not produce a good result.

In most cases, the mixture will not sit well on surfaces. It will also not have a uniform color or consistency.

Water-based polyurethane on the other hand is more accommodating to enamel paints. You can mix water-based enamel with water-based polyurethane to give a strong and colored polyurethane finish. But even this should be done carefully. If you mix too much water-based enamel paint with polyurethane, you are at risk of thinning the polyurethane.

So to be on the safer side, don’t mix Polyurethane with enamel. If you must, ensure to do so carefully or ask for help.

Is Spray Enamel The Same as Polyurethane?

Spray enamel is not the same as polyurethane although both products are advertised as high-gloss topcoats. There are also enamel products that are designed with polyurethane additives. These products are called polyurethane enamels. But they are still not the same as polyurethane.

Spray enamel refers to enamel paint that comes in spray cans. These enamel products are usually used to seal enamel paints. This makes the spray enamel a top coat or sealant. However, it’s not the same as polyurethane.

Polyurethane is a finishing product designed with diisocyanates or isocyanates and polyols (alcohol). The polyol reacts to the isocyanates or diisocyanates to form the polyurethane finish.

Spray enamels on the other hand go through a different chemical process. Spray enamels are designed with lead and other resins. The resins react to form the spray enamel finish.

Asides from the chemical hardening process of both topcoats, there are also differences in their finishes. Polyurethane is known to be thicker and more durable than spray enamel. Spray enamels on the other hand are known to dry faster than polyurethane, especially oil-based polyurethane.

The notion of similarity between polyurethane and spray enamel is because both topcoats can be sprayed from paint cans. They can also be used on virtually the same type of surfaces which makes DIYers feel both topcoats are the same.

Can I Use Enamel Over Polyurethane?

Enamel paint can be used over polyurethane as long as the polyurethane finish has cured and is lightly scuffed. But the enamel paint should have the same base as the polyurethane.

Most polyurethane finishes are oil-based. So to apply enamel paint over oil-based Polyurethane, it’s advised to use oil-based enamel paint.

However, for water-based polyurethane, you can use both oil-based and water-based enamel paint. This is because oil and water-based paints will adhere to water-based poly but water-based paints will not adhere to oil-based polyurethane.

When it comes to painting over polyurethane with enamel paint, there is usually a bit of investigation and work to be done. This is because polyurethane is a sealant and as such, it is not designed to be painted over.

Rather, polyurethane is designed to be applied over other paints. So the first problem you will encounter when painting over Polyurethane with enamel is paint bonding.

To minimize this problem, you need to find out which type of polyurethane was used and you can do this using the water test.

Apply a few drops of water on the polyurethane and leave it. If the water turns white or remains clear, then the polyurethane is water-based. If the water turns black or tinted, it’s oil-based polyurethane. When you know the type of polyurethane, you’ll know the type of enamel paint to use over it to improve adhesion.

Use water or oil-based enamel over water-based polyurethane. Then use only oil-based enamel over oil-based polyurethane.

Light sanding is very important to make the new paint coating stick to the polyurethane.

Final Words

Overall, you can apply polyurethane over enamel. You just need to scuff the enamel paint first and apply 3 coats of polyurethane over it.

However, you should never apply water-based polyurethane over oil-based enamel. It’s also not a good idea to apply enamel over polyurethane since polyurethane is designed as a sealant.

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