Polyurethane is one of the most durable finishes out there. But, polyurethane is bound to chip and crack eventually. So, when this happens, can you paint over the polyurethane?
You can paint over polyurethane. But you must degrease, sand, and wipe the sealant first. This is to allow the paint to penetrate and stick over it. It’s also easier to paint over water-based than oil-based polyurethane.
Also, applying a coat of stain-blocking primer over the sealant will improve the adhesion.
Paints won’t stick to polyurethane directly. That’s because, when dry, the sealant forms a hard and moisture-resistant film that prevents liquid penetration.
For paint to stick, they need to penetrate into the surface. This is why they stick to porous surfaces better because they penetrate the wood pores easier. However, the moisture-resistant finish of the sealant doesn’t allow the paint to penetrate its coating, so it won’t stick.
The moisture-resistant finish also prevents liquid (oil or water) to penetrate it. Since all paints are water or oil-based, they won’t be able to penetrate it.
Polyurethane when dry has a natural slick glossy top coat. So, if you apply a coat over it, the coating will slide off the sealant finish. This makes it very difficult for any paint to stick over a sealant.
However, you can sand, prime, and remove (some parts) polyurethane to allow a new finish to stick over it. Sanding will remove the glossy top coat, and the primer will create an undercoat for the paint to bite into.
Do You Need To Sand and Prime?
If you want a proper adhesion, you must sand and prime the sealant. If you don’t, the paint won’t stick well over it and will peel off eventually. The paint will stay on the polyurethane initially. But, it will crack and peel off after a few days because it will have poor adhesion.
The purpose of sanding is to remove the glossy layers of sealant. And, the purpose of priming is to create an undercoat so the new coating can stick better.
Here are other things that can happen if you don’t sand or apply a primer:
- Poor adhesion.
- The new finish will get affected (removed) by moisture.
- Poor durability.
- The new coating will turn sticky or tacky.
- You won’t be able to seal the finish.
- You will have to remove the finish.
How To Paint Over Polyurethane?
Here are the tools and supplies you need:
- Medium and fine-grit sandpaper
- A scraper
- Degreaser or cleaning solvent
- A brush or spray gun
- An oil-based primer
- A gallon of paint
- A pair of gloves
- Breathing protection
- Wood filler (optional)
- A sealant
1. Degrease and Clean The Finish
First, degrease and clean the finish. Cleaning removes the dirt and dust from the surface and allows the new coating to stick better. If you don’t clean, the dirt will prevent good adhesion and will bleed through the new finish.
To clean it:
- Use TSD (Trisodium Phosphate) or a cleaning solvent, such as vinegar or white spirits.
- Pour the solvent over the finish using a cloth.
- Wait 5 minutes.
- Use a dry rag to wipe the degreaser and stains off.
- Rinse the finish with clean water.
2. Repair and Fill Cracks in The Surface
It’s unlikely that have cracks or holes in a polyurethane-coated item, but if there are any cracks or dents, you should repair and fill them. If it’s a wooden item, fill the cracks and holes with a wood filler.
You can also use caulk on items like plaster, drywall, and wood trim. For concrete and masonry, use concrete paste.
3. Sand or Degloss The Finish
Before painting over a glossy finish you must sand it off. To sand it, start with medium-grit sandpaper (150-grit). The medium-grit sandpaper will remove stubborn stains and dust nibs. Then, finish off with fine-grit sandpaper.
The fine-grit sandpaper (220-grit) will even out the grain and smoothen the surface. While sanding, don’t press too hard on the sandpaper because you can damage (or remove) the entire sealant. After adding, wipe off the dust.
If you don’t want to sand polyurethane, you can use deglosser. It’s a powerful product that will remove the glossy layer of a sealant.
If the surface is too large to sand, use a deglosser to speed it up. To apply deglosser over the sealant, pour it into a clean rag, and use the rag to wipe the sealant. Wait a few minutes, and the deglosser will remove the glossy layer of the sealant.
4. Apply Primer
Priming creates a textured coating for the new coating to stick to. You need 1-2 coats of primer over the sealant. It’s recommended to use oil-based primer over polyurethane. This is because polyurethane has a high level of solvents and oils compatible with an oil-based primer.
Apply the primer using a paintbrush. Allow each coat to dry before you apply the next one. It takes oil-based primer 1 hour to dry enough for a re-coat.
5. Apply The Paint
It’s recommended to apply paint using a spray gun. A spray gun will apply the coating faster, get more coverage, and won’t leave brush marks behind. However, you have to thin it before spraying.
You need 3 thin coats of paint over polyurethane. Let each coat dry before applying the next one. If you used an oil-based primer, it’s better to use oil-based paint, such as enamel, over it.
6. Seal The Paint (Optional)
Sealing the finish is optional, but it will make it last longer. You can use gel stain, lacquer, wax, or any other sealant. Leave the finish for at least a day before sealing it.
You Don’t Have To Remove Polyurethane Completely
You don’t have to remove polyurethane before painting over it. As long as the finish is still in good condition, you just need to sand it and apply a coat of primer to allow the paint to stick better.
But, if the finish is defective, you need to remove it. For instance, if the finish is wet or peeling, you should remove it.
Also, if the polyurethane is oil-based, you should strip its top glossy layer. Oil-based polyurethane has a harder finish, and as such, will be more difficult to paint over. So, the best bet is usually to remove it.
However, you don’t always need to remove the entire polyurethane coating. You only need to remove some of it to allow the new coating to bite and stick well. This process is known as “stress sanding”. You have to sand only areas that will experience heavy use.
Paints To Use:
You can use chalk paint over polyurethane because it has impressive adhesive qualities and will stick over all surfaces. But, you need to sand the sealant’s glossy finish first before applying it.
You can use enamel since it’s an oil-based paint. However, it’s necessary to prime the sealant first.
You can use latex paint over a glossy finish since it’s flexible and will cope with a sealant well. But, you need to prime the sealant first.
Some spray paints can go over polyurethane, and others don’t. Some sprayers contain different types of chemicals and additives — some of these chemicals will not stay on a sealant. For instance, sprayers with high levels of silicone will not stick well.
Acrylic has impressive bonding qualities and will stick over most surfaces, including a glossy one. However, you must sand and prime the sealant first before applying it.
You can apply milk paint over water-based polyurethane. Milk paint has a formula with just water and color, it doesn’t have binders and adhesives. So, it wouldn’t stick well to an oil-based sealant.
Related Read: Can You Apply Polyurethane Over Old Polyurethane?
Overall, you can paint over polyurethane. Though the sealant is used as the final coat, it can be a basecoat too. All you need to do is degrease, sand, and wipe it.
But, for the best results, it’s better if you remove the entire sealant finish first.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,