Yes, you can put polyurethane over paint. However, there are a few tips and tricks to get the quality finish you seek. There are also one or two things you shouldn’t do unless you want to spend a lot of money and waste a lot of time.
I like polyurethane in certain applications. While I’m a great fan of more natural finishes such as waxes and oils, there’s no doubt that polyurethane is hard to beat for a low-maintenance surface finish.
Recently I’ve read many articles that make incorrect claims and statements regarding the use of polyurethane over paint. When I read such misinformation, I get concerned as it wastes people’s time and money while not giving the required quality of finish. Stick with me for the next few minutes, and I’ll address all issues you need to understand when applying polyurethane over painted wood.
Can you put polyurethane over paint?
Yes, you can. Applying polyurethane over a painted surface offers several benefits:
- Polyurethane adds a layer of protection against weathering and UV damage
- Depending on your choice of polyurethane, colors can be enhanced and deepened
- Your surface is more resistant to scratching, impact, and general wear
- When applied correctly, you can extend the time between repaints
Can you put polyurethane over acrylic paint?
Yes, you can put polyurethane over acrylic paint. Some of our readers get concerned about whether oil-based polyurethane will go over acrylic paint. They’ve been advised to use only water-based polyurethane. However, this advice is wrong.
Let’s clear this up. Once an acrylic paint has fully cured, it is irrelevant which type of polyurethane you apply. If you have allowed the acrylic paint to cure fully, the water has evaporated, and the resins and the pigments will have hardened using a cross-linking process. A full cure for acrylic paint takes approximately 21 to 30 days.
Applying an oil-based polyurethane over correctly cured acrylic paint will not harm it. Your decision on which polyurethane to use is dictated more by the color you apply it over and the look you wish to achieve. Follow the instructions later in this article for the best method of application to ensure correct adhesion.
Can you put polyurethane over latex paint?
Yes, you can put polyurethane over latex paint. However, the latex paint must be fully cured. Note I said cure, not dry. Latex paint will be dry in 24 to 48 hours. However, for the chemical reaction to have completed, which completely hardens the paint, allow 21 to 30 days.
There are a few simple steps to follow to get the best result when applying polyurethane over latex paint. We will give you those steps later in this article.
Can you put polyurethane over chalk paint?
Yes, you can put polyurethane over chalk paint. As with all other paints, the chalk paint must be cured fully. The curing process will take about 21 to 30 days.
A point to consider is that most people apply chalk paint to get a soft, matte finish, particularly if they’re after the shabby chic look. Applying polyurethane will detract from that look by adding a satin finish, making it look less flat.
Again, check out the steps to follow later in this article which will take you through the entire process, from choosing the correct polyurethane to correctly applying it.
Can you put polyurethane over enamel paint?
Yes, you can put polyurethane over enamel paint. Whether the polyurethane is water-based or oil-based, both make good surface protection for enamel paint.
As with all paints, you must allow them to cure fully before you attempt to apply the polyurethane. Enamel paints cure more quickly than latex and acrylic paints, but they’ll still take about 7 to 14 days to cure fully.
Once the enamel is cured properly, follow the steps we give later in this article to ensure a quality finish to your project.
How long should paint dry before polyurethane?
Put this query in Google, and you’ll find many people confusing the terms dry and cure. The two terms are very different. Confusing drying and curing times could mean the difference between a high-quality job and starting again.
Dry is a term meaning that you can carefully handle the item. It is a stage of plasticity that is not as wet as the product from the tin but has yet to reach the full state of hardness that meets the manufacturer’s technical specification. You can usually mark the surface with your fingernail.
The term cure means that the paint covering has reached its final state of hardness. There will be no further chemical changes or changes in the coating’s physical characteristics.
Depending on the paint, some will be dry in 2 to 3 hours, while some oil-based products may take 6 to 8. While adding additional coats of the same paint may be approved by the manufacturer, applying a coat of a different product may ruin the surface. Applying polyurethane too soon could cause adhesion problems or prevent the paint from fully curing.
Most paint will cure in 21 to 30 days, although enamel paint may take less time at 7 to 14 days. Once the paint is cured, you can safely apply your polyurethane, knowing that you will do no damage.
How to apply polyurethane over paint
See our article for an in-depth guide to using polyurethane and a list of tools you’ll need. However, the following steps will guide you.
- Decide which polyurethane you want to use. I’d choose oil-based for exterior surfaces, darker colors, and objects subjected to heat, moisture, or surface wear and abrasion. Water-based is great for interior use, lighter colors, or objects that may receive knocks.
- Ensure the paint has completely cured. Allow 30 days for all paints except enamels, in which case I’d allow 14 days.
- Wash the painted surface. Wash the entire surface with detergent and water. Rinse well with water and dry completely.
- Sand the surface. Lightly sand the surface with 120 or 180 grit sandpaper. You’re not seeking to remove paint, but to lightly scratch the surface to create a keying surface that assists the polyurethane in adhering.
- Vacuum the surface. Vacuum thoroughly and wipe the surface over with a painter’s tack cloth to remove all sanding dust.
- Prepare the polyurehane. Gently stir the polyurethane before decanting some into a clean, dry container. If you’re using oil-based polyurethane, thin it with mineral spirits at a 75/25 ratio of polyurethane to thinner. Thinning helps oil-based polyurethanes to flow smoothly, preventing air bubbles. Water-based polyurethane does not need thinning.
- Use the right brush. Select a synthetic brush for water-based polyurethane and a natural bristle brush for oil-based products.
- Apply polyurethane. Dip the tip of the brush into the polyurethane, then allow the excess to drip back into the tin. Do not wipe the brush on the side of the tin, as you’ll entrap air in the bristles and get air bubbles in your finish.
Use light strokes to apply the polyurethane to the painted surface. Aim to get coverage, but do not overwork the area as you’ll introduce air bubbles while leaving a rough finish as the polyurethane dries.
- Allow polyurethane to dry. Water-based polyurethane will be dry enough to sand in two to three hours. Oil-based polyurethane will need 12 to 24 hours. Learn more about polyurethane drying times in this article.
- Sand the polyurethane. Once the polyurethane is dry, lightly scuff the surface using 220-grit sandpaper and remove all dust using a vacuum and tack cloths, as before.
- Apply another coat. Apply a second coat of polyurethane. If you are using oil-based products, thin it with mineral spirits at a 75/25 ratio of polyurethane to thinner.
How many coats of polyurethane to apply over paint?
If you are using oil-based polyurethane, two coats are fine, maybe three if you need strong protection. Water-based polyurethane will need three to five coats to give the same protection.
How long to let polyurethane dry between coats?
If you are adding a second coat of polyurethane, wait 3 hours for a water-based product and 8 to 12 hours for an oil-based one. If you try to sand over a polyurethane that isn’t properly dry, you can ruin the finish.
What type of polyurethane to use over paint?
We’ve discussed that you can apply any polyurethane over the top of properly cured paint. However, there are some aesthetic considerations to consider.
Oil-based polyurethane has a very light amber tint. When applied to timber or paint, it deepens and richens the color of the underlying surface. If applied over a color like white, you will see the light yellow tinge, which may detract from the look you wish to achieve. Oil-based polyurethanes are best used over darker colors, or when you wish to richen the look of the underlying surface.
I also like to use oil-based polyurethanes for exterior purposes as they last longer. You’ll hear a lot of talk about water-based polyurethanes being ‘almost as long-lasting’ as oil-based products. However, water-based products will routinely last 5 to 7 years against the 8 to 10 years of oil-based polyurethanes.
Water-based polyurethanes appear milky white in the tin but dry clear. They are used when top coating a light color, and you do not wish the yellowing effect of oil-based polyurethane. Also, use them when you wish to preserve the underlying color of the paint or wood grain. Water-based polyurethanes are a great choice for internal use. While they’re more expensive, they dry quickly, allowing room occupancy in a shorter time.
For an in-depth look at the differences between oil-based and water-based polyurethane and where to use them, we’ve written this article to assist.
Tips for applying polyurethane over paint
There are four enemies to a good polyurethane finish:
- Dirty or flaking paint
- Air bubbles
- Lack of adhesion
Follow these tips, and you’ll have everything working in your favor for a good quality result.
- Ensure the paint is cured properly, not just dry. Allow 21 to 30 days for most paint and 14 days for enamel.
- Be sure to clean the surface well, as described in the steps above. Lightly sand the surface with 120 to 180 grit sandpaper. Vacuum and use a tack cloth to remove sawdust.
- Use the correct brush for the type of polyurethane. Synthetic for water-based, and natural-bristle for oil-based. Whichever brush you choose, use a high-quality one with a fine tip and bristles. With brushes, quality equates to cost.
- Only load the first half-inch to an inch of brush with polyurethane. To avoid air entrapment in the bristles, allow the brush to drain excess polyurethane naturally, rather than scrubbing against the tin.
- Hold the brush at a 10 to 15-degree angle in the direction of travel – using just the tip of the brush applied lightly to the surface.
- Always thin oil-based polyurethane with mineral spirits. If you fail to do so, you have a far greater likelihood of getting air bubbles in your finish.
- Don’t go over and over the same area with wet polyurethane. Get the coverage you need with one or two passes maximum, then allow the polyurethane to flow and smooth naturally before drying. Overworking gives a rough finish and adds air bubbles.
- Always let the polyurethane dry properly before recoating. If you try to apply a second coat when the first is only surface dry, you can end up dragging the surface. In that case, you’ll have to remove all the polyurethane you’ve applied and start again.
- Always scuff sand between coats. Polyurethane doesn’t like sticking to itself and requires a keying surface for maximum adhesion. Forget this step, and you won’t get the life you want from the finish.
Read More: How to Fix Polyurethane Mistakes
Can you mix polyurethane with paint?
The answer to this is sometimes yes, and sometimes no. The more important question is whether you should mix polyurethane with paint. However, let’s first discuss which paint mixes with polyurethane and which doesn’t.
Latex paint and polyurethane do not mix, regardless of whether the polyurethane is oil-based or water-based. The reason lies in the way latex paint cures. Most paints cure through a chemical reaction; however, latex cures by evaporation.
Add latex paint to polyurethane, and you’ve got one product trying to cure through a chemical process with air and the other trying to cure through evaporation. Neither will dry correctly, and you’ll end up with a horrible sticky mess.
Acrylic paint will not mix with oil-based polyurethane. Try adding some cooking oil with water and see what happens. That’s what will happen with acrylic and oil-based polyurethane. The two will not mix, and you’ll have wasted a lot of money and made a real mess.
Acrylic paint will mix with water-based polyurethanes, just as oil-based paints will mix with oil-based polyurethanes. However, just because you can, should you? If you’re considering mixing paint and polyurethane, ask yourself why you want to. The polyurethane will not make the paint more glossy or improve the finish, and you risk affecting drying times, adhesion, hardness, and appearance.
If you’re looking to tint polyurethane slightly, you can add a drop or two of paint with the same base. However, be sparing as a couple of drops is usually sufficient. However, I’m not a fan, and I’d suggest purchasing pigments specifically designed for the purpose.
A lot of chemistry goes into individual paint products, and by mixing them, you’re entering an unknown world. My advice is to apply the paint, let it cure fully, and then apply the polyurethane.
Frequently Asked Questions
How do you know when the paint is dry enough for polyurethane?
The paint must not just be dry but be allowed to cure fully. That requires 21 – 30 days for most paints and 14 days for enamel paint.
What happens if you apply polyurethane before the paint is dry?
You can find the paint or polyurethane doesn’t dry properly, remaining soft. You may also find the adhesion is compromised, with the finish not lasting. Worst case, the finish is muddy, or the surface will be rough. You’ll need to strip off everything and start again.
What to do if you applied polyurethane over paint that wasn’t dry?
That depends on the look. If the polyurethane finally dries and the look isn’t too bad, you may choose to do nothing. However, you’ll only know how long the coating lasts when it starts to fail. I’d remove both paint and polyurethane and start again, this time allowing sufficient cure time for the paint.
Can you put water-based polyurethane over oil-based paint?
Yes, you can. As long as the oil-based paint is fully cured and you clean and scuff sand the paint surface, water-based polyurethane will adhere well.
Can you put oil-based polyurethane over water-based paint?
Yes, you can. As long as the water-based paint is fully cured and you clean and scuff sand the paint surface, oil-based polyurethane will adhere well.
Can you put polyurethane over spray paint?
Yes. As with any other type of paint, the spraypaint must cure fully. A lot of spray paint is enamel, and therefore it cures quickly in approximately 14 days.
Polyurethane Over Paint Conclusion
Applying polyurethane as a topcoat to paint is not difficult if you observe some basic steps. Once a base coat has fully cured, you can apply whatever form of polyurethane you wish. Use patience, and follow the steps we’ve outlined, and you’ll end up with a high-quality and long-lasting finish to make you proud. Good luck.