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 paint. But you must degrease, sand, and wipe the polyurethane before painting over it. This is to allow the paint to stick and dry properly.
It’s easier to paint over water-based polyurethane than oil-based polyurethane. Also, a coat of stain-blocking primer over the polyurethane finish will make the paint stick and perform better.
But that’s not all. There is more to know about painting over polyurethane and this post digs right into the topic. Let’s dive in.
Does Paint Stick To Polyurethane?
Paint won’t stick to polyurethane properly. Polyurethane when dry, forms a hard and moisture-resistant film that prevents paint from sticking. So, polyurethane doesn’t have the requirements needed for the paint to stick.
For paint to stick, the paint coating needs to bite into something. That’s why paints stick to porous surfaces like wood since the paint can bite into the wood. However, due to its moisture-resistant finish, polyurethane doesn’t allow the paint to bite into it.
The moisture-resistant finish of polyurethane also prevents liquid (oil or water) to penetrate it. Since all paints are water or oil-based, the paint will not penetrate to the polyurethane.
Polyurethane when dry has a natural glossy top coat. This glossy top coat is slick, if you put paint over it, the paint coating will slide off the polyurethane coating. This makes it very difficult for any paint to stick to polyurethane.
For paint to stick to polyurethane, you have to sand and primer polyurethane first. Sanding will remove the glossy top coat of the polyurethane, and the primer will create an undercoat for paint to bite into.
Sand or Prime Polyurethane Before Painting?
Painting over polyurethane without sanding or priming isn’t recommended. If you do, the paint will not stick properly.
The paint will stay on the polyurethane initially. But, the paint will crack and peel off after a few days. That’s because if you don’t sand and primer polyurethane, the paint will have poor adhesion.
The purpose of sanding is to remove the glossy layers of polyurethane. And, the purpose of priming is to create an undercoat so the paint can stick better.
But, that’s not all. Here are other things that can happen:
- The paint will not adhere well to the surface and can be wiped off.
- The paint will be affected by heat and moisture.
- The finish will not be durable.
- The paint will turn sticky or tacky.
- It will be impossible to seal the finish.
- You’ll eventually have to remove the paint and start all over.
How To Paint Over Polyurethane?
Here are the tools and supplies you need:
- Medium and fine-grit sandpaper
- A paint scraper
- Degreaser or cleaning solvent
- A paintbrush or spray gun
- An oil-based paint primer
- A gallon of paint
- A pair of gloves
- Breathing protection
- Wood filler (optional)
- A sealant or top coat
1. Degrease and Clean The Polyurethane
First, degrease and clean the polyurethane finish. If the surface is dirty, the paint won’t stick properly. Also, grease on the polyurethane can bleed through the paint and ruin the finish.
To degrease the polyurethane, use TSD (Trisodium Phosphate) or a cleaning solvent like vinegar or white spirits.
Pour some solvent over the polyurethane coating using a cloth. Cover every area of the polyurethane. Leave the degreaser for 5 minutes to work. After 5 minutes, use a dry rag to wipe the degreaser and the stains off the polyurethane.
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 Polyurethane
Painting polyurethane without sanding isn’t recommended. Sanding helps the paint stick better and helps the finish come out smooth. To sand, start with 150-grit medium-grit sandpaper. The medium-grit sandpaper will remove stubborn stains and dust nibs.
Then, finish off with fine-grit sandpaper. Fine-grit sandpaper (220-grit) will even out grain and smoothen the surface. While sanding, don’t press too hard on the sandpaper or you’ll ruin the polyurethane. After sanding, wipe off the dust.
If you don’t want to sand polyurethane, you can use deglosser. Deglosser acts as fine-grit sandpaper. It’s a powerful product that will remove the glossy layer of polyurethane.
If the surface is too large to sand, use a deglosser to speed it up. To apply deglosser over polyurethane, pour deglosser into a clean rag, and use the rag to wipe the polyurethane coating. Wait a few minutes, and the deglosser will remove the top layer of polyurethane.
4. Apply Paint Primer
Priming creates an undercoat for the paint to stick to. You need 1-2 coats of primer on the polyurethane. 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.
Once both coats of primers are dry, you can apply the paint.
5. Apply The Paint
It’s recommended to apply paint using a spray gun. A spray gun will apply the paint faster, get more coverage, and won’t leave brush marks behind. However, you have to thin the paint 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 over it. Enamel paint is a good choice because it works well with polyurethane and it’s a strong and durable paint.
You can also use water-based paint over the oil-based paint primer. But, the primer is compatible with water-based paints.
6. Seal The Paint (Optional)
Sealing the finish is optional, but it will make the paint last longer. You can use gel stain, lacquer, wax, or any other sealant over the paint. 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 polyurethane finish is still in good condition, you can paint over it. You just need to sand the polyurethane and apply a coat of paint primer to allow the paint to stick better.
But, if the polyurethane is defective, you need to remove it. For instance, if the polyurethane paint is wet or peeling, you should remove it before painting over it.
Also, if the polyurethane is oil-based, you should strip the top glossy layer. Oil-based polyurethane is harder than water-based polyurethane, and as such, will be more difficult to paint over. So, the best bet is usually to remove the oil-based polyurethane first. To paint over water-based polyurethane, you don’t have to remove the top layer.
However, you don’t always need to remove the entire polyurethane coating. You only need to remove some of it to allow the paint to bite and stick well. This process is known as “stress sanding”. You have to sand only areas that will experience heavy use.
For instance, on a polyurethane-coated desk, the stress areas will be the tabletop and the edges. These areas will see constant use and where the paint is most likely to come off first. So you need to ensure proper paint adhesion in these areas.
When you sand the stress areas, the paint will stick and become stronger so it’s less likely for the paint to come off.
What Paint Will Stick to Polyurethane?
Here are some different types of paint that you can or can’t use over polyurethane:
You can paint over polyurethane with chalk paint. Chalk paint has impressive adhesive qualities and will stick to every surface, including polyurethane. But you need to sand the polyurethane before putting chalk paint over it.
Chalk paint is water-based, so you should use a water-based primer over polyurethane before applying chalk paint. Chalk paint is also thick so to spray the paint, you’ll have to thin it with equal parts of water.
You can paint over polyurethane with enamel paint since enamel paint is an oil-based paint. However, it’s necessary to prime the polyurethane first. Since enamel paint is oil-based, it would glide off the glossy layer of polyurethane. So you need to cover the polyurethane with a primer to allow the enamel paint to stick.
You can paint over polyurethane with latex paint. Latex paint is flexible, so it will cope with polyurethane very well.
But, you need to prime the polyurethane first. Latex paint is water-based and won’t stick to the glossy finish of polyurethane without a primer.
Some spray paints can go over polyurethane, and others don’t.
Spray paints contain different types of chemicals and additives — some of these chemicals will not stay on polyurethane. For instance, spray paints with high levels of silicone will not stick well to polyurethane paint because silicone repels paints.
So, before you put spray paint over polyurethane, check if the spray paint can be used over polyurethane sealant. Spray paints that contain urethane will work perfectly on polyurethane.
Acrylic paints can be used over polyurethane. But, like all water-based paints, you need to sand and prime the polyurethane paint first to allow the acrylic paint to stick.
However, some types of acrylic paint don’t do well over a polyurethane coating. So, check if the acrylic paint you use is compatible with polyurethane.
Milk paint can be used over polyurethane. But, milk paint works better with 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 polyurethane.
You should also know that milk paint is not known for its durability. So, seal it with a protective sealant to prevent the finish from chipping.
Related Read: Can You Apply Polyurethane Over Old Polyurethane?
Overall, you can paint over polyurethane. Though the paint is used as the final coat, it can be a basecoat too. All you need to do is degrease, sand, and wipe the polyurethane to allow the paint to stick.
Also, you don’t need to remove the entire polyurethane coating to paint over it. You have to sand the stress areas to give the paint good durability.