The short answer is of course you can! How can you put polyurethane over paint? The short answer is easy! Moreover, on some occasions, you even should. But you know exactly how I roll, so buckle up, and let’s dive into the depths of the topic.
There is a lot to covet in this seemingly simple topic. I’ll take a quick dab on the nature of polyurethane, then we’ll go a bit deeper to take a look at the interactions of polyurethane with different types of paint.
After that, there will be some practical recommendations and the final descent to the most common questions.
- 1 What is polyurethane?
- 2 Common types of polyurethane
- 3 Do you really need polyurethane over paint?
- 4 Can you put polyurethane over paint of different types?
- 5 Mixing polyurethane with a paint
- 6 Practical recommendations on applying polyurethane over paint
- 6.1 Safety measures
- 6.2 Tools for applying polyurethane over paint
- 6.3 Preparation of painted surface and application
- 6.4 Other relevant tips
- 7 Q&A bit
- 8 Wrapping it up
What is polyurethane?
In general, polyurethane is the name of the broad variety of plastics, but when it comes to woodworking and similar field, polyurethane is the name for topcoat products that contain polyurethane resin.
Along with polyurethane resin poly, clear coats contain water or oil to provide needed viscosity and other additives. Water or oil evaporates after application, leaving a layer of resin behind. After that, resin cures, forming a durable film that sticks firmly to most painted surfaces.
Tip. Get more useful information about How long does polyurethane take to dry.
Common types of polyurethane
Every manufacturer has their formula for polyurethane clear coat, but there are two general categories divided by the base: water or oil. The type of base defines the safety, drying, and curing features of every product, as well as its interactions with various types of paints.
Pro-tip: Use water-based polyurethane to cover water-based paints if you plan to put the topcoat before the complete curing of the paint layer. The same goes for oil-based polyurethanes over oil-based paints. Once the paint is completely cured, the type of polyurethane doesn’t actually matter.
In terms of interacting with paints, oil-based polyurethane gives them a slight amber tint that becomes more obvious with time (I mean years of time). Such an effect is more prominent when the topcoat is exposed to UV.
So, I usually go with oil-based poly if the underlying paint could use some additional tint. But keep in mind, that oil-based polyurethanes have a strong odor and require mineral spirits for dilution and clean-up. Also, mind the interactions with other paints.
Water-based polyurethane is easier to apply, has no odor, and can be diluted and washed away with water. It produces a clear coat that tends to stay clear throughout its term of use. I prefer water-based for the majority of projects.
In terms of applying polyurethane over some paint, it is the best option, especially if the paint is already completely cured. But, if the paint is water-based too, you can apply polyurethane on wet paint. Just make sure there’s no water left in it.
Pro-tip: Spray gun allows you to apply polyurethane even earlier since it implies no direct contact with the surface of the paint and the layer of topcoat is thin.
Do you really need polyurethane over paint?
That depends mostly on the type of paint and desired finish. In general, a layer of poly will provide additional protection for your paint, while maintaining its sheen (there are high-gloss, semi-gloss, and matte types of poly).
Enamel paints, for instance, are tough enough on their own, while acrylic paints or chalk paints could use some scratch protection. In fact, you don’t even have to cover the whole piece with poly. A couple of layers on areas with the highest traffic, such as countertops, are enough.
The flooring will look great and serve well with a coat of polyurethane. Of course, such a surface will need proper maintenance and renovation every 5-9 years.
Outside wooden constructions (decks, gazebos, etc.) could use protection too, but make sure to use a designated type of polyurethane. Such products usually have additives that improve their UV resistance.
Tip. Furthermore, you can read more about How many coats of polyurethane on table.
Can you put polyurethane over paint of different types?
Now, with all the basics sorted out, we can proceed to the features of interactions of poly with different types of paint. The mindful and tidy application will provide:
- additional durability;
- desired type of sheen;
- more time between repaints.
Tip. You can learn more about Can you paint pressure-treated wood?
Polyurethane over acrylic paint
Poly goes pretty well on top of the acrylic paint. Usually, I go for water-based polyurethane on top of dried (not cured) acrylic paint. It goes down well and does not mess up the curing process of acrylic paints.
If the acrylic paint layer is older than 30 days, then it’s OK to use oil-based poly. Especially if there is a need to make the color a bit warmer. Just don’t forget to roughen the surface a bit for better adhesion.
Polyurethane over latex paint
Latex paint is often water-based and very similar to acrylic ones in terms of content. There should be no troubles with the application of polyurethane over a dried layer of latex paint. Especially, because such paints are usually thinner and tend to dry faster.
If you have or want exclusively oil-based poly, give the latex paint layer some time to cure, at least in its outer layer.
Polyurethane over chalk paint
A chalk paint coat is gentle by its nature, so it requires a protective layer of sorts in cases when it’s not temporary.
There are designated chalk paint waxes, but water-based polyurethane will do too. A couple of thin coats will protect the surface from deep scratches that will inevitably appear without a topcoat.
Oil-based polyurethane is fine too, but you’ll have to dilute it with some paint thinner to provide the needed viscosity to go over the chalk paint without any issues.
Polyurethane over enamel paint
Enamel paint is usually durable, so there’s not much point in the application of poly on top for protection. However, you might go for it to receive the desired type of sheen. I had used matte or semi-gloss poly to knock that usual enamel gloss.
When it comes to application, both oil-based and water-based poly will go over a dried layer of high gloss paint with zero issues. Of course, in the case of tidy and gentle application. See the practical recommendations on the application below.
Polyurethane over paint in spray form
Well, spray paint is not a separate kind of paint in terms of contents. It is rather a convenient form of packaging. Acrylic paint can be spray paint, as well as some oil-based paint.
You should have no problems with the application of polyurethane varnish on top of spray paint on various pieces while you stick to general recommendations on the process.
Mixing polyurethane with a paint
That’s the tricky part. Some enamel paints come premixed with polyurethane varnish. As for the rest types of paints, there’s no actual need in mixing poly into the paint.
Mixing some acrylic paint into polyurethane varnish is actually a great idea to make your topcoat look better. Adding some designated dye will help the coat truly flourish. Just remember a couple of things:
- Always mix water-based paint into water-based poly. The same goes for oil-based polyurethane and oil-based paint. Otherwise, you’ll ruin your products, as oil and water don’t actually mix.
- You’ll need literally just a couple of drops of paint, and that will be enough to tint poly.
- Wet and dry colors are different. Paint a piece of cardboard to have an idea of how your finish will look.
There are quite plenty of physical and chemical processes involved in the drying and curing of both paints and polyurethanes. It is really easy to mess things up by mixing different products without certainty of outcome.
Practical recommendations on applying polyurethane over paint
The painted surface preparation and tidy application are the cornerstones of a good polyurethane topcoat. Let me guide you through some practical recommendations regarding the selection of application tools, techniques, and vital tips for applying polyurethane.
Water-based polyurethane requires no special safety measures. Of course, you would want some gloves to protect the skin. Oil-based polyurethane contains some mineral spirits with toxic chemicals and a strong odor, so a respirator is needed to work with it safely.
Also, you’ll have to use mineral spirits and paint thinners to dilute it.
A respirator is also necessary while using a spray gun or poly in a spray can with no regard to the actual type of the product. Both oil-based and water-based polyurethanes produce fine particles when sprayed. You don’t want those particles anywhere near your lungs, for sure.
Tools for applying polyurethane over paint
Similar to the majority of projects, you can get away with some sandpaper, brush, and rags on one hand. On the other hand, you also can use intricate sanding machines and fancy spray guns. The sweet spot depends on the scale of your project, the frequency of similar jobs, and, of course, available funds.
Surface preparation tools
Sandpaper is the main mean for the painted surface preparation. You can use it freehand, on a sanding block, or with a sanding machine of sorts.
Chances are you’ll combine those methods to get to nooks and crannies and cover broad flat areas faster. Also, you need it to scuff the first coat before application of the rest of them.
180-300 grit range is optimal. The more imperfections there are on the surface of the paint, the rougher the grit should be.
On top of it, you’ll need something to clean the paint surface thoroughly after sanding. Tack cloth will suffice, but nice vac will be even better.
Note: Refrain from degreasing the paint with some usual degreasers, sanding will do the trick instead. If you decided to wash the surface anyway, let it dry completely before poly application.
There are a number of tools to apply polyurethane finish (if it isn’t in the form of a spray):
- bristle or foam brush;
- rags for wiping on;
- spray guns.
Each of them is completely suitable for the job, but has its features and requires a bit of practice. Don’t hesitate to practice a bit on some scraps before application on the actual piece. It will save a lot of time.
Pro-tip: Make sure to have some spare applicators (foam or bristle brushes) at hand to be able to replace the ones that became unusable.
To keep the whole process tidy, you’ll need to cover the floor and any surrounding painted surfaces with a material that will catch all the splatter and dripping. Used cardboard boxes or some designated film will suffice.
Pro-tip: Painters masking film rolls are relatively cheap and great for covering parts of the painted surface that need no polyurethane, as it comes with some tape attached to their edge.
Also, you’ll need some containers to mix and dilute polyurethane in. Go for disposable cups of sorts.
Tip. Also, you can read more about How to remove polyurethane from wood.
Preparation of painted surface and application
Now, you should have picked the type of your poly and prepared all the needed tools and other stuff. You also have all the basic info. Let’s move to actually putting polyurethane over the paint. And in the first place, you’ll need to make sure that the painted surface is dry enough.
Press your nail against the surface of the paint. If it leaves no visible mark, then you’re good to go. And if there are any doubts, just let it sit for another day or so.
Pro-tip: Always check the state of the paint on parts of the piece that are away from plain sight.
Try to do everything possible to decrease the amount of airborne debris in the room where you will apply polyurethane. Such precaution will prevent dust and other particles from corrupting the fresh clear coat.
Step 1: Surface preparation
Lightly sand the surface of the paint at first. There’s no need to go hard on it, just some light scuffing to knock down height differences, hide deep scratches, and create some relief for the poly to stick even better. Apply as low pressure as possible. Try not to sand through the paint layer.
There should be no sanding dust and debris on the surface after sanding. Tack cloth, brush, or vac will do the trick. A blow gun will do too. Some woodworkers recommend wet rags, but I usually go for thorough dry cleaning to save time on waiting for the surface to dry.
Step 2: First coat application
Once all painted surfaces are clean and roughened a bit, it is OK to apply polyurethane coating with your applicator of choice. Each of them has nuances:
- use a synthetic bristle brush for water-based poly and a natural bristle one for oil-based products;
- submerge only the third part of the bristle or foam length into the poly to decrease bubbling;
- do not wipe the excess on the side of the container, let it drip away naturally instead to decrease bubbling;
- dilute the poly with 25-50% by volume to use wipe on technique;
- dilute the poly with 10% of water or mineral spirits for application with a spraying gun.
Try to distribute the poly evenly over the surface and don’t touch the surface of the poly when it starts to dry and becomes tacky. The key is to leave no visible boundaries between areas of freshly applied poly and the ones that already started drying. Let the first coat dry.
Pro-tip: Water-based poly is drying faster, so you’ll have to find and maintain a suitable tempo for the whole application process.
Step 3: Preparation for a second coat.
After the first coat is dry enough (fingernail test will show), it is time to give it a little scuffing with some 300-grit sanding sponge or paper. This step is needed to knock down any debris particles that got caught on the first layer. It is also a great opportunity to hide any uneven parts of the surface.
Naturally, you will need to wipe or blow away all the sanding dust from scuffing. The same old cloth, brush, or vac will do for this step too. And there are no official limitations on how many coats you can apply.
Note: There’s no actual need in sanding the first layer if you are using a spray gun and able to produce a thin, even layer. But some time between coats is still needed.
Step 4: Second coat application
Second and all the following coats can be thicker, but keep them as tidy and uniform as you can. Remember that the polyurethane tends to flow and even out before it starts to dry. You can lightly sand each layer, but it is optional.
Step 5: Waiting and observing
After that, you can just wait for the whole final coat to dry. Drying and curing times depend on the properties of the given product and some ambient conditions. Refer to the packaging to have an idea of how long it may take.
If you are going for an extra glossy mirror-like finish, you’ll have to polish the completely cured final coat with respective compounds. Or you can use the wipe-on technique. Both options will require patience and practice for the best outcome.
Keep an eye on the drying piece to see if there are problematic areas. You will be able to see bubbles in places with bad adhesion or other troubles.
Step 6: Cleaning up
Clean-up after using water-based poly is as easy as washing everything with soapy water. Cleaning up after oil-based polyurethane would require some mineral spirits or paint thinner. And chances are your brushes won’t be usable even after that.
Pro-tip: Never forget to wash your spray gun. Any leftover poly residue may clog it and just ruin a good tool.
Other relevant tips
There are some additional moments I would like to point out:
- water-based polyurethane looks milky in the can and immediately after application, but it will become clear after drying (it happens because fine resin particles aren’t dissolved in water)
- don’t apply too much pressure in the brush to prevent bubbling;
- go for long steady passes with a brush to maintain uniform spreading of poly;
- don’t go over areas that start drying as it may result in smearing, and it is much harder to fix;
- read the product’s label to provide the best possible conditions for drying and curing (temperature, airflow, humidity).
Tip. You can read my guide and learn more from the post on How to get paint off wood floors.
Now, that you know everything about the application of polyurethane over painted wood, let me take a moment to answer some related questions.
What happens when you put polyurethane over paint?
Nothing special if the paint is cured or, at least, dry. If the paint is not completely cured, but dry and has the same base as the poly (water or oil) nothing bad will happen too. Both layers will just dry and cure to form a nice finish.
But putting oil-based polyurethane over water-based paints or water-based poly over oil-based paints will result in a ruined finish. It won’t dry, at the very least.
Why would you put polyurethane over paint?
The main reason is protection. Polyurethane will add a durable finish on top of the paint and protect it from physical, chemical, and even biological influences. The same goes for wood under the paint too.
The second reason is appearance. There are polyurethane varnishes with various sheens to completely fulfill the design. Can you put polyurethane over the paint for both protection and looks? Of course, it is a great idea.
How long should the paint dry before applying polyurethane?
12 to 24 hours after application and depending on the type of paint. If paint and poly have the same base, there’s no actual need to wait for the complete curing of the paint.
Find the “dry to touch” time on the packaging of your product, adjust it to ambient conditions, and it will be time to wait before applying polyurethane. Add a couple of additional hours or even a day to be completely sure. It won’t hurt.
Wrapping it up
And that’s it for now. That’s all you need to know to understand that you can put polyurethane over paint and can do it yourself. There’s nothing too complicated, just remember not to mix products with different bases, and all the rest can be fixed.
My name is Alex Mashinsky
I am an enthusiastic woodworking hobbyist who created topwoodworkingtools.com to provide helpful information and advice to fellow woodworkers.
The goal of the website is to help readers make informed decisions about woodworking tools and materials, with the ultimate aim of ensuring that they achieve the best possible results from their projects.
My main focus is on offering accurate, honest, and well-reasoned opinions and advice to help readers choose the most suitable tools and materials for their particular needs.