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

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

You can apply polyurethane over enamel paint to increase the durability and moisture resistance of the finish. When dry, it 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, it will stick to the glossy layer of enamel paint.

Polyurethane Types To Use

Oil-based polyurethane works best with enamel paint they have the same paint solvent (oil) and are compatible. Also, this sealant is more durable and works better for outdoor surfaces. 

You can also use water-based polyurethane, but the paint must be fully dry (cured) before you apply it. If it isn’t, the finish will turn sticky (or tacky) as the solvent of the water-based poly (water) and enamel (oil) aren’t compatible and don’t mix well.

You can also use exterior polyurethane for outdoor surfaces as it is formulated with extra additives that make it more durable and resistant to outdoor elements.

How To Apply Polyurethane Over Enamel Paint?

Applying polyurethane to enamel paint isn’t hard, but you must wait until the finish fully dries before sealing 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

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 Finish

Clean the finish to remove dust and filth. If you don’t, the dust will prevent the sealant to stick over it. The dust and filth will also show once the polyurethane dries since it has a transparent finish.

To clean it:

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 coating using a clean rag. 

3. Sand The Finish

Once the enamel paint finish is clean, sand it. Sanding removes imperfections from the surface, removes the glossy layer of finish, and evens out the surface allowing the sealant 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 it, remove the dust and re-clean the surface. 

4. Apply Polyurethane

You can use water-based, oil-based, or exterior polyurethane, but oil-based or exterior polyurethane works better. If the sealant is too thick, thin it.

To thin oil-based polyurethane, use mineral spirits and thin it in a ratio of 4:1 (4 parts poly, 1 part thinner).

To apply it:

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 finish to fully dry (cure) before using it. 

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

Mixing Them

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,  you can’t mix enamel with water-based polyurethane as they have different solvents, water and oil. Oil and water have different drying times, so if you mix them, 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 finish first. If you apply it directly, the paint won’t stick 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 paint won’t stick.

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

Final Words

You can use polyurethane to seal enamel paint from moisture, water, and scratches. However, the finish must be clean and lightly sanded before sealing it.

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