Polyurethane Over Enamel Paint: (How To Do it & Benefits)

Enamel paint is a durable paint and has minimal water-resistance features. However, if exposed to constant water (or moisture), enamel paint washes off. So, can you apply polyurethane over enamel paint?

You can apply polyurethane over enamel paint to increase the durability and moisture resistance of the finish. When dry, polyurethane forms a glossy clear coat that protects the enamel paint from water, moisture, scratches, and other damage. 

Polyurethane is a topical topcoat, meaning it doesn’t need to penetrate the surface to stick. So, polyurethane will stick to the glossy layer of enamel paint.

Polyurethane Types To Use

Oil-based polyurethane works best with enamel paint. That’s because oil-based polyurethane and enamel paint have the same paint solvent (oil). So, oil-based poly and enamel are compatible. 

Oil-based polyurethane is more durable and harder than water-based polyurethane. So, for outdoor enamel paint surfaces, use oil-based or exterior polyurethane.

You can also use water-based polyurethane, but the enamel paint must be fully dry (cured) before you apply it. If the enamel paint is still wet and you apply water-based polyurethane, the finish will become tacky. That’s because the solvent of water-based poly (water) and the enamel paint (oil) aren’t compatible.

You can also use exterior polyurethane for outdoor enamel-painted surfaces. Exterior polyurethane has extra additives, making the finish more durable and resistant to moisture and weather elements. 

How To Apply Polyurethane Over Enamel Paint?

Applying polyurethane over enamel paint isn’t hard, but you must wait until the enamel paint is dry before applying it. 

Here are the tools you need:

  • Tack Cloth or Rags
  • Fine-Grit Sandpaper
  • Bristled Paintbrush
  • Drop Sheet
  • Polishing Compound (Optional)

1. Prepare The Workspace

Prepare The Workspace

First, prep your workspace. Cover nearby objects and furniture and lay a drop sheet over the floor. This prevents paint spills on the floor. 

2. Clean The Enamel Paint

Wipe The Enamel Paint

Before applying polyurethane, clean the enamel paint finish. If you don’t clean the enamel paint finish, the dust and filth will show since polyurethane is a clear coat. Also, dust prevents polyurethane from sticking properly. 

To clean enamel paint finish:

  1. Use warm soapy water or rubbing alcohol. 
  2. Damp a clean rag with warm soapy water. 
  3. Wipe the surface with the dampened rag. 
  4. Wait 5 minutes.
  5. Remove the solvent residue from the enamel paint using a clean rag. 

3. Sand The Finish

Sand The Enamel Paint

Once the enamel paint finish is clean, sand it. Sanding removes imperfections from the surface, removes the glossy layer of enamel, and evens out the surface allowing polyurethane to stick better. 

To sand enamel paint, use fine-grit sandpaper (220-grit). Sand lightly as you need to smooth the surface, not remove the entire coating. 

After sanding the enamel paint finish, remove the dust and re-clean the surface. 

4. Apply Polyurethane

Apply The First Two Coats of Polyurethane

Once the enamel paint finish is sanded, apply polyurethane. You can use water-based, oil-based, or exterior polyurethane over enamel paint. Oil-based and exterior polyurethane work best with enamel paint.

If the oil-based polyurethane is too thick, you must thin it. To thin oil-based polyurethane before applying it over enamel, use mineral spirits. Thin polyurethane in a ratio of 4:1 (4 parts polyurethane, 1 part paint thinner).  

To apply polyurethane over enamel paint:

  1. Use a paintbrush, roller, or sprayer. 
  2. Apply 3 coats of polyurethane over enamel paint.
  3. Wait until one coat dries before applying the next one. 
  4. Allow the final coat of polyurethane to fully dry (cure) before using it. 

When dry, polyurethane will form a glossy clear coat over enamel paint, protecting it from moisture, water, and scratches. Polyurethane also improves the durability of the enamel paint, helping it last longer. Since polyurethane has no color (no paint pigments), it doesn’t change the color of the enamel paint finish. 

Mixing Polyurethane With Enamel Paint

You can mix enamel paint with oil-based polyurethane, and acrylic enamel paint (water-based) with water-based polyurethane. However, mixing enamel paint with water-based polyurethane won’t work because of the difference in the paint base (solvent).

A mixture of oil-based polyurethane and enamel paint will create a colorful and durable finish. Since polyurethane has no color (no paint pigments), you must mix it to tint the finish color. However, you must use more polyurethane than enamel to get a durable and stable finish.

But, can you can’t mix enamel with water-based polyurethane. Enamel paint uses oil as its paint solvent, while water-based polyurethane uses water as its solvent. Oil and water have different drying times, so if you mix water-based poly with enamel paint, the finish won’t dry properly and will turn sticky. That’s because one part of the finish will dry while the other paint will still be wet. This leads to a cracked paint finish.

Applying Enamel Paint over Polyurethane

You can use enamel paint over polyurethane, but you must sand and scuff the polyurethane first. If you apply enamel paint directly over polyurethane, the paint won’t stick. That’s because polyurethane has a glossy finish that repels liquid, including paint. 

Enamel paint must penetrate the surface to stick. But, since polyurethane repels liquid (it doesn’t allow them to penetrate the surface), the enamel paint won’t stick.

However, sanding will produce tiny ridges (scratches) on the polyurethane that the enamel paint can penetrate into and stick. But, enamel paint won’t last too long. So, the best way to apply enamel over a polyurethane coating is to remove the polyurethane and then apply enamel paint. 

Final Words

You can apply polyurethane over enamel paint to seal it from moisture, water, and scratches. However, the enamel paint coating must be clean and lightly sanded for polyurethane to stick. 

On the other hand, you can’t apply enamel paint over polyurethane unless you sand or remove the polyurethane. That’s because polyurethane forms a glossy layer that prevents liquid from penetrating it. Since enamel paint can’t penetrate the polyurethane coating, the paint won’t stick.

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