I have read several shellac manufacturer instructions that you should never put polyurethane over shellac.
Some reputable wood finishers say the same.
After getting several questions from you guys, I decided to test it myself, to answer the question, can you put polyurethane over shellac?
Stick around and let me answer your question.
But first things first, if you’re new to woodworking, you need to understand the difference between shellac and polyurethane before proceeding.
Okay, done, let’s get started;
Can You Polyurethane Over Shellac
Polyurethane shouldn’t be put over shellac because shellac covers all. However, there’re cases where shellac finished woodworks buff out white marks when a splatter of water gets on it and the fix is to strip off the shellac and refinish it with poly.
If you must put poly over shellac, follow the steps below, but before doing so, here are the tools you’ll need.
- Dewaxed shellac/ waxed shellac
- Pure Minwax fast-drying polyurethane
- Denatured alcohol
- Dampen paper towel
Step 1: Dilute the shellac
Dilute thin 1 part of 3/4-pound-cut shellac with 4 parts denatured alcohol. Stir the mix.
Step 2: Sand the wood
Using your favorite sandpaper, sand the wood surface.
Step 3: Apply the first coat
Apply a thin coat of the diluted shellac using the brush, then leave the wood for 45 minutes for the shellac to soak in well and dry.
Ensure to apply thin coats of shellac to make the polish stronger and less apt to crack.
Learn More: How long does shellac take to dry?
Step 4: Sand the wood surface
Lightly sand the wood, then wipe off the dust using a dampened paper towel.
Step 5: Apply the poly
Using a different brush, apply the polyurethane over the shellac and leave it to dry for about 3-4 hours.
Step 6: Sand the wood once more
Sand the wood one more time after the top coat of polyurethane has dried
Step 7: Apply the last coat
After sanding, use a dumped paper towel to dust off the dust, apply the final coat of polyurethane, and give it 3-4 days to cure.
Shellac under Polyurethane?
Shellac is a strong sealer that doesn’t require any topcoat finish with polyurethane. If you’ve been worrying about putting poly over shellac, worry no more.
Dewaxed shellac is compatible with water-based finishes like polyurethane. To add, it is often used as an “adapter” layer and can go over, or under, water or oil-based poly.
Despite being compatible with most finishes, I am unsure if shellac is compatible with lacquer and catalyzed finishes.
Pro Tip: The above is true when using the “dewaxed” type of shellac because shellac with wax isn’t compatible with other under/over finishes.
Can You Put Polyurethane Over Zinsser Shellac?
Zinsser shellac manufacturers don’t recommend applying poly over shellac. However, they raise many questions by saying, poly is okay when applied over the Zinsser sanding sealer product.
So, you may be asking, what’s the right path to take?
I did some tests, put Minwax poly over Zinsser amber shellac and everything looked ok to me.
Can You Put a Top Coat Over Shellac?
Putting a top coat over shellac is possible.
However, be prepared to face a lot of problems to take it off.
You’ll need to use a nail polish remover which must be acetone-free. If you don’t, you’ll end up ruining both applications.
Additionally, it is ok to apply regular nail polish over shellac. However, never put shellac over regular nail polish because it won’t cure right.
Similarly, can you apply a coat of shellac over the topcoat?
Yes, you can.
Sometimes I do 3 coats of it to add strength and color. The problem is, you’ll need more time to remove it as acetone needs to penetrate through all the layers.
And if you’re wondering how you can make the Shellac coat last longer, then consider the following tips:
- Never rush the drying.
- Let it stay moisturized.
- Avoid direct sunlight when drying.
- Apply a top coat to it.
Can shellac be painted over?
Shellac can be painted, but unlike painted cabinets, its glossiness doesn’t hold paint.
Before you apply paint to it, extra preparation will be required. First, remove the shellac before applying the paint. This is, so you keep the paint from flaking off the surface later.
How Long Does Shellac Need To Dry Before Applying Polyurethane?
Unlike polyurethane which can take up to 24hours to dry well, shellac doesn’t take long. If you don’t over-apply it, it should take 1 hour before sanding or screening.
The second coat should dry within 2 to 3 hours.
This finish is less durable and also less scratch-resistant than polyurethane.
Can you apply shellac over polyurethane?
You can apply shellac over polyurethane even though this wonderful finish covers everything.
This is so because it will stick to the poly just fine. The drawback is, poly is a soft/flexible material, while shellac is hard/inflexible, so if polyurethane moves, the topcoat (shellac) won’t move and can crack over time.
Find if you can shellac over stain?
Will Clear Shellac Raise Wood Grain?
Shellac contains alcohol in shellac, and to my experience, it will fail to raise the grain of wood. Just sand the first coat lightly with 320 or 400 grit sandpaper when it’s dry before the next coat.
Do You Have To Sand Shellac Before Poly?
Whether you’re using oil-based or water-based poly, you must sand/scuff shellac to allow it to have a superb bond.
Poly Over Shellac
So, you’ve learned it is possible to apply polyurethane over shellac. I believe you enjoyed the read.
If you follow the steps provided for spraying polyurethane over shellac, you will be able to get great finishes in the end.
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