Polyurethane is a standard synthetic resin used in multiple woodworking applications.
But as the finish ages, you must consider beautification strategies such as painting, lets discuss the topic, can you paint over polyurethane?
You can paint over polyurethane. However, prepare the surface by sanding and priming before painting.
Otherwise, the finish will not bind correctly, causing bubbling, cracking, and other related issues.
Surface preparation is vital as it improves the chances of the formula to adhere properly over the polyurethane finish.
Cleaning, sanding, priming before priming will help the paint to stick to polyurethane for an extended duration.
Painting wood requires a lot of learning and practice. Besides, trial and error can only go so far.
So, read this article for more insight into painting polyurethane surfaces and how to strip the finish if needed.
Table of Contents
What Is Polyurethane?
Polyurethane is a thin transparent liquid finish.
The formula’s primary purpose is to protect the surface from water, fungus, scratches, and mildew.
But it also highlights the wood grain and imparts a golden tone.
Polyurethane finishes resemble shellacs, varnishes, and lacquers. However, they are essentially plastic and different from shellacs made from organic products.
Usually, the product is an organic polymer comprising organic units linked using urethane molecules.
You can categorize it among thermosetting polymers as it does not melt upon heating.
Nonetheless, there are some specific polyurethane types exhibiting thermoplastic attributes. Hence, it is easy to melt and remold them.
Conventional polyurethane preparation techniques involve chemical reactions between di- or tri-isocyanates and polyols.
The formula is an alternating copolymer with two monomer types undergoing polymerization.
In addition, both isocyanates and polyols have at least two functional groups in every particle.
Polyurethanes, epoxies, unsaturated polyesters, and phenolics are reaction polymers.
You can prepare them using chemical reactions between isocyanates and polyols.
However, these reactions need a catalyst or some ultraviolet light to overcome the energy barrier activation.
Polyurethane’s attributes highly depend on how you produce them. For instance, the final product will be soft and elastic if the polyol chain is long and flexible.
Conversely, the result will be challenging and rigid when the cross-linking extent is too great.
The product’s cross-linked structure comprises three-dimensional networks. Thus, you can expect very high molecular weights.
This structure also accounts for the polymer’s thermosetting nature. So, polyurethane does not melt or soften with heat exposure.
Further, polyurethanes can form foams, one of their most desirable qualities.
You achieve this result by producing carbon dioxide during the urethane polymerization process.
Also, you can produce the polymer’s high-density microcellular foams without blowing agents.
Polyurethane’s applications include:
- Foams production: These foams are ideal for materials like domestic furniture, upholstery fabrics, and refrigerator sheets.
- Columns and door frames’ molding: Some woodworkers use these moldings in window headers and balusters.
- The product’s flexibility makes it perfect for mattresses, automobile seats, and upholstery. You can also use it for elastic straps and bands.
- Polyurethane’s low-density elastomers are essential in the footwear industry.
- The formula also makes bathroom and kitchen sponges and comes in handy in seat cushions and couches production.
The varnish can be water- or oil-based.
Most woodworkers prefer the former because it’s more environmentally friendly and cost-efficient.
However, it is prudent to go through both types for better decision-making. Check out the product details below.
Water-based polyurethane uses water instead of solvents as its base. Further, it forms a hard protective coating, protecting the surface from elements.
The finish dries quickly. Hence, you can apply more coats in less time.
Also, water-based polyurethane is milky-white in the can but delivers a transparent surface after drying.
Thus, you don’t have to fear that the finish will impart color to the project.
Moreover, this product does not have an odor, and water and soap deliver good clean-up.
Consider using water-based polyurethane if you have aversions to handling messy, odorous formulas.
In addition, the solution is perfect when you want a thinner and more flexible finish. For instance, one or two coats are nearly invisible with almost no build.
Finally, delivering a hard shell appearance with a water-based formula is possible. But you need numerous layers.
This varnish type gives a hard shell-like surface and leaves a yellow hue. Also, it makes paint durable and works best for outdoor woodwork.
Oil-based polyurethane utilizes various mineral and petroleum solvents as vehicles.
They come in brush and spray-on formats and create a hard protective surface. Further, you need lesser coatings to get optimal performance.
Oil-based formulas dry slowly. One coat needs about two hours, whereas additional layers take approximately six hours.
However, this duration lengthens depending on room and exterior conditions.
Woodworkers find the product’s odor sharp and pronounced as it dries. Fortunately, the smell goes away once it cures, allowing you to use the workpiece without discomfort.
Oil-based polyurethane needs paint thinner or mineral spirits for effective clean-up.
Further, the finish is self-leveling, meaning it becomes smooth when applied to a horizontal area.
Consider spraying the polyurethane to guarantee even, professional results.
Oil-based coatings are a perfect choice for cabinets, countertops, wood floors, and railings where durability is essential.
In addition, they deliver superior scratch and abrasion resistance, maintaining a rich, golden glow.
When applying multiple coats, it is advisable to give the product extra curing time. Fortunately, you only need a few coats to deliver a satisfactory outcome.
Confine your oil-based polyurethane finish to areas with plenty of ventilation. Prolonged exposure to its odor causes health hazards.
Generally, the product requires loads of patience and time for perfect results.
How to Paint Over Polyurethane
A polyurethane finish is a durable coating protecting wooden surfaces.
Hence, you can’t paint directly over it. Otherwise, the paint will not adhere properly.
Nonetheless, you can paint over polyurethane with the right supplies and a little effort.
Start by cleaning the wood and filling in any blemishes and cracks. Then, sand it to enhance primer and paint adhesion.
NB: Consider enamel paint if you are not stripping the finish. And remove the sheen from the surface before painting.
Here is a more detailed procedure.
Clean and Prepare the Surface
Get safety glasses, a facemask, and rubber gloves. Although trisodium phosphate is a potent cleaning formula, it is also toxic.
Therefore, wear safety clothing to avoid spills and splashes.
In addition, work in a well-ventilated work area. Use fans and open up windows to increase circulation when working indoors.
Combine a quarter cup of TSP with one water gallon in a container. Use a medium-sized bucket for convenience.
Fill the vessel with water and pour the TSP slowly. Then, use a wooden spoon or stir stick to blend the mixture.
Be careful not to splash the solution when stirring. Also, use a clean bucket to avoid adding dirt to the surface.
Alternatively, you can use a milder cleaning solution.
Fill a bucket with one warm water gallon and add one tablespoon of dish soap.
Get a sponge with a rough, scrubbing surface and dip it into the cleaning formula. Then, wring out the excess.
Apply gentle but firm pressure and wipe the surface in circular motions.
This way, you remove any grime, dust, dirt, and other residues without damaging the surface.
Further, spread the cleaning solution over stubborn stains and grime and scrub with a bristled brush.
Let the surface dry completely. It would be best to wait about ten minutes.
Then, lightly touch it with your finger to confirm dryness. If the surface feels damp, wait five more minutes and check again.
Use a clean, dry lint-free rag to wipe the surface and speed up drying. Only ensure that it is dry before you sand or paint.
Fill in any holes, cracks, and chips with wood putty and allow it to dry.
Wood putty fills breaks and lumpy regions to deliver a uniform and smooth surface. But read the packaging instructions for specific drying times.
Also, apply just enough paster to form an even layer and fill visible imperfections.
You can get the wood putty at home improvement stalls, hardware stores, and online.
Sand the Surface
Sanding polyurethane creates dust and flakes that can irritate your lungs and throat. Hence, wear a face mask for maximum safety.
Alternatively, you can tie a bandana to cover your nose and mouth.
Scrub the surface with fine-grit paper, preferably between 120- to 220-grit. In addition, utilize small, circular motions and work in portions.
You do not need to strip all the polyurethane. Just remove enough to allow the primer and paint to stick.
Consider getting an automatic sander when working with extensive surfaces. Also, switch to a 60- or 80- grit paper for a smoother finish.
Vacuum all the dirt from the surface and surrounding regions. Use a standard vacuum cleaner’s hose or shop vac to suck the dust directly.
Wipe the surface with a clean, wet rag. Run it over the entire surface to clear additional dust.
You can also utilize damp paper towels or sponges to clean the surface.
Priming the Surface
Get a bristled brush for smaller surfaces and a foam roller for extensive ones.
Also, use a paint roller when you want to cover more area. It will deliver a better outcome for walls, tables, and doors.
A one- to two-inch paint brush will help cover smaller, more detailed surfaces like antique dressers and baseboards.
Most paint jobs need a roller and a brush.
The roller helps iron out broad surfaces, and the brush covers smaller areas like edges and trim.
The next step is to choose a white, oil-based primer for perfect coverage and adhesion.
Open the primer can and stir the formula with a paint stirrer. It helps break up solids and combine them.
Next, pour the primer slowly into a clean paint tray. But please avoid overfilling the reservoir.
You will need the paint tray’s textured ridges to scrape off excess formula.
Dip the roller or brush into the formula. Then, roll and brush the paint using smooth up and down motions.
In addition, apply a thin and uniform primer layer.
Give the finish enough time to dry. Further, you can check the product label for specific drying durations.
Also, use your finger to confirm if the surface is dry.
Then, add a second primer coat when covering dark-colored polyurethane or dark lumber.
Paint the Surface
Oil-based formulas adhere better to the primer and polyurethane and last longer than water-based ones.
Open the paint can and stir the formula thoroughly. Then, pour the paint into a clean tray.
Further, ensure the tray does not contain primer residue. Otherwise, the latter will dilute the paint and compromise its adhesion, color, and appearance.
You can visit a home improvement store, local paint supply store, or go online to check your paint options.
Next, apply a thin paint layer with a paintbrush or roller. Also, work in sections and spread the formula using up and down strokes.
Use smooth, consistent motions to guarantee a thin, uniform layer.
Do not panic if you can see through the first paint coat. Sort the issue by applying at least two paint coats.
Let the paint dry before adding subsequent coats. Wait for about half an hour, then check with your finger.
Check the manufacturer’s directives for specific curing times. And do not compromise on them.
Otherwise, the coats will not adhere correctly or form a smooth, uniform surface.
Here’s a Video on Painting Over a Glossy Finish Like Polyurethane:
Can I Paint Over Polyurethane Without Sanding?
Technically, you can paint over polyurethane without sanding. But you need a specialty formula to prepare a polyurethane finish for painting.
Further, painting directly over polyurethane only ends with peeling. Hence, you’ll need to sand and primer the surface first.
Failing to prepare the workpiece makes it vulnerable to peeling, even by a single fingernail scratch.
Consider using a good-quality primer to protect the surface’s color and guarantee a smooth painting exercise.
In addition, we have primers designed for hard-to-paint workpieces. Therefore, you can go straight to priming and still deliver a professional finish.
However, the above is a risk.
Moreover, there is always a probability of the toughest primer not bonding well to polyurethane.
For instance, high gloss finishes may compromise the result if you skip the sanding stage.
If you insist on using a specialty product, test the coating on a scrap workpiece to see if sanding is necessary.
This way, you’ll see potential issues.
How to Paint Over Polyurethane Without Sanding
Most woodworkers argue that sanding is the effective way when painting over polyurethane.
But we have alternatives such as applying a deglosser or using chalk paint.
Applying a Deglosser
A deglosser is liquid sandpaper. It etches the finish and gives the paint a new texture to adhere to.
Thus, the product is a perfect option for furniture pieces with multiple intricate details.
Unfortunately, the chemical is pretty strong. And it is advisable to use eyewear and skin protection during the operation.
In addition, ensure you work in a well-ventilated area. This way, you avoid damaging your respiratory system or giving yourself a headache.
Test the deglosser on a small, inconspicuous spot before applying it to the entire surface. Then, evaluate whether the chemical ruins the wood.
Using a deglosser is pretty straightforward. Dip a lint-free cloth into the formula and wipe it over the workpiece.
Moreover, you do not have to rub or rinse the surface forcefully. Allow it to air dry naturally.
Using Chalk Paint
Woodworkers perceive Chalk Paint as a miracle formula; it can go over surfaces without prior preparation.
The paint’s matte finish gives it a rustic vibe.
Also, you can apply it to any clean and dry surface. But consider a few exceptions, like a glossy polyurethane finish.
The formula is pretty effective. It can even work on previously painted surfaces without needing any prep work.
The chalk paint will peel off if you do not sand through the gloss.
How Do You Prep Polyurethane for Painting?
Ideally, prepare the polyurethane surface for painting to deliver the desired outcome. Thus, sand or use a deglosser and then primer the workpiece.
No one likes sanding as it is a tiresome part of most Do-It-Yourself projects. But you can only ensure good results by removing the polyurethane.
Fortunately, you do not need to remove all the finish. Roughing the surface with fine grit paper is enough to guarantee paint adherence.
Nonetheless, sanding is vital when you intend to stain the lumber with a different shade.
Moreover, the surface will not absorb the formula if it has a protective finish.
Use progressively finer sandpaper grits to restore the wood’s smooth finish. In addition, it is possible to remove the yellowed varnish with a few sanders passes.
Alternatively, consider a drum sander attachment for sanding holes and concave curves. Then, remove all the dust with a tack or damp cloth before painting.
A deglosser is liquid sandpaper. Further, it works perfectly for intricate details or nooks and crannies.
You can also use it for large workpieces that would take forever to sand.
The formula acts like fine-grade sandpaper and etches the polyurethane finish. This way, the paint sticks better.
However, it is a potent chemical. Thus, consider having the proper skin and eye protection.
In addition, test the deglosser on an inconspicuous spot on the project.
Besides, it is prudent to confirm that the product does not ruin the wood. Then, saturate a clean cloth with the solution and wipe the surface.
Lastly, let it dry, and you are ready to paint.
You can prime the surface with a good quality primer if you do not want to sand or use a deglosser.
Besides, the formula ensures the paint will stick properly. You will also need fewer coats to deliver full coverage.
Sand the primer quickly with 220-grit sandpaper. Then, clean the workpiece with a tack cloth before painting.
This way, you will remove brush strokes and ensure a flawless appearance.
Can You Paint Over Polyurethane Kitchen Cabinets?
You can paint over polyurethane kitchen cabinets. Ensure you have everything needed for a professional outcome.
The supplies include:
- Mineral spirits
- Clean, lint-free rags
- Wood filler
- Protective face mask
- Liquid sandpaper
- Fine-grade sandpaper
- Oil-based primer
- Oil-based paint.
Next, follow the how-to steps below.
Always read the product manual and follow the recommended safety directives. Wear protective gear if the manufacturer calls for it.
In addition, the accessories keep your lungs, eyes, and hands safe.
Work in a well-ventilated area as some chemical fumes are toxic and harmful to your health.
Dispose of rags soaked in mineral spirits or oil-based primer and paint correctly. Soak them in water to reduce fire risk.
Remove Hardware Such as Cabinet Doors and Drawers
Remove the cabinet knots to facilitate better coverage. But you can leave them in place when working with a few cabinets.
Clean and Fill the Kitchen Cabinets
Use mineral spirits and the recommended solvents to clean the wood. Also, wipe it in circular motions.
This way, you remove grime, stains, and dirt and guarantee a better paint finish.
Moreover, evaluate the cabinets for any gaps and scratches. Then, get a suitable wood filler to conceal them.
Sand the Surface
Use fine grit paper to remove the polyurethane finish from cabinet doors. However, you do not need to remove all of it.
Light scuffing will still facilitate paint adhesion.
Continually wipe the sanding dust with a clean cloth and mineral spirits. Further, take your time.
Sanding is a tedious part of this project, yet the most important.
Fortunately, liquid sandpaper is another strategy for removing polyurethane topcoats. Only ensure you follow the manufacturer’s directives to deliver the desired result.
Prime the Surface
Apply an oil-based paint primer. It gives the finish a better surface to adhere to and prevents stains from coming through the finish.
Allow the primer to cure overnight for the best outcome.
Also, you can add another layer if the wood grain shows through the primer.
Paint the Surface
Apply the first coat and let it dry overnight. Then, add a second coat to deliver better coverage.
Finally, allow the finish to dry for 72 hours before resuming use or adding hardware.
How to Remove Polyurethane from Bare Wood
Sometimes you want to refinish furniture or touch up hardwood floors but are unsure how to remove the polyurethane coating.
Worry not! Here is a detailed procedure to get you started.
However, please do not forget to prepare yourself and the work area for enhanced safety and convenience.
Prepare Yourself and the Work Area
Typically, you need chemicals to remove a polyurethane finish. And since they are often harsh, it is prudent to ensure good ventilation.
Consider going outside if you can and create cross ventilation when working on floors.
You can create cross ventilation by opening the windows and doors in the room. Also, set up a fan blowing inward and another blowing outwards.
Put something on the floor to shield it from drips and stains.
A plastic tarp is an excellent accessory. In addition, you can tape down the edges to minimize tripping.
Please protect yourself. Paint stripper is harmful if you are not careful.
Therefore, wear rubber gloves to protect your hands, a respirator to keep the fumes from your lungs, and goggles to protect your eyes.
Also, wear closed-toe shoes, pants, and long sleeves if possible. Do not leave anything to chance.
Choose the paint stripper wisely. We have chemical- and water-based strippers.
Chemical-based strippers like methylene chloride are pretty effective. But they are harmful to the skin and can cause respiratory issues.
On the other hand, water-based strippers are more environmentally friendly. But they need more time to work.
Apply the Paint Stripper
Paint a generous stripper coating on the surface. Further, coat the polyurethane finish until it is wet.
Use a paint roller or an old paintbrush and cover all the nooks and crannies.
The type of brush should not worry you.
Besides, getting one you are willing to throw away after the application is advisable.
Let the paint stripper soak into the finish. Besides, it will do the work for you, so give the process ample time.
Usually, ten minutes are enough for most chemical-based strippers.
You will know the exercise is complete when the polyurethane finish starts bubbling and wrinkling.
Conversely, water-based strippers need more time, even six to 24 hours. But confirm with the product label for accurate timelines.
Always cover the project during breaks.
Sometimes you need to leave work for an extended period. Please ensure the stripper remains wet.
Besides, the formula must be wet to properly penetrate the polyurethane coat. So, use a plastic tarp and place it tightly over the flooring or furniture.
Scrub Off Polyurethane
A metal scraper is an excellent place to start. However, consider a plastic one if you do not want to scratch the surface.
The polyurethane coat should peel off quickly as you move along. Moreover, the paint stripper does all the hard work.
Scrape in the wood grain’s direction. Otherwise, you risk damaging the furniture and floors.
In addition, scratches along the wood grain will not affect the surface’s overall pattern.
Use a steel brush to cover small areas. Besides, a scraper will not work in curved and decorative locations.
Instead, scrub with a metal brush. The bristles will remove the polyurethane even in all the nooks and crannies.
Get an after-wash solvent to rub down the finish. Further, it cleans up the polyurethane and removes the paint stripper.
Use a rag or paper towel to rub the surface and continue until you remove the entire coat.
Evaluate the surface. Then, apply another paint stripper layer and scrape the wood when necessary.
Sand the surface after removing the polyurethane. You can use fine steel wool or 150 grit sandpaper.
The grit smoothens the wood and removes the remaining finish.
Soak discarded cloths and steel wood in water to reduce fire risk. In addition, dispose of the water and rags in a hazardous waste disposal unit.
Lastly, please avoid throwing this waste directly into the sewer or trash.
Frequently Asked Questions
The questions include:
Can I Put Polyurethane Over Chalk Paint?
Absolutely yes! Besides, most woodworkers prefer polyurethane instead of a traditional wax finish.
Polyurethane is more durable than its counterpart and protects the surface from moisture damage.
Therefore, it will preserve your chalk paint finish for longer.
What Precautionary Tips are Needed When Painting Over a Polyurethane?
Woodworking professionals advocate for safety first when painting over polyurethane. Further, the exercise involves harsh chemicals that risk your skin and eyes.
In addition, processes like sanding produce dust harmful to your respiratory system.
Work in a well-ventilated room or place when preparing for the paintwork. For instance, open the door and windows or set up a fan when working indoors.
Also, avoid prolonged exposure to any chemicals despite ensuring proper air circulation.
Wear protective gear when stripping the polyurethane finish or doing the paintwork. For example, wear your goggles and rubber gloves to protect your eyes and skin.
It is also prudent to use a respirator. Painting chemicals have toxic fumes that cause adverse health effects like nausea, headaches, and dizziness.
In addition, get a protective mask to protect your lungs.
Furthermore, working at extreme temperature levels poses a threat.
Most painting chemicals are highly flammable. So, avoid smoking or working around heat-generating appliances.
Please do not work in rainy weather and check the forecast for sunny or calm days.
Cold days compromise the curing process, causing cracks and ruining the entire paintwork.
The most suitable temperature for the project is 75 degrees Fahrenheit.
Can You Paint Over Water-Based Polyurethane?
Painting over water-based polyurethane is another way to update your furniture’s appearance.
Besides, it is a pretty straightforward exercise if you have the correct supplies and procedure.
Water-based polyurethane delivers a slick finish and compromises paint adhesion. Thus, cleaning and sanding it for a lasting surface is advisable.
Start by washing the polyurethane finish with a grease-cutting detergent and dry it properly.
Next, scuff the surface with sandpaper. You can use your hand or get a power sander with 200-grit sandpaper.
Vacuum the sanding dust and wipe the workpiece before painting.
Apply a good quality oil-based primer coat and let it dry for 24 hours. Then, add the paint coats.
It is wise to choose an appropriate painting day. So, choose a slightly hot and dry day.
Otherwise, cold and damp conditions compromise the curing process. And you will end up with deep cracks or an orange peel texture.
Ideally, choose a non-rainy day ranging between 50 to 70 degrees Fahrenheit.
Apply three paint coats over the primer to deliver a solid finish. But allow each layer about 24 hours before adding the next.
Adding a second coat before the first one cures causes the paint to bubble up, peel, or crack later.
Thus, you’ll have to strip off the paint and start over. How frustrating!
Can I Sand Polyurethane?
You can sand in between polyurethane coats, but not the final one. In addition, give the first coat a 24-hour drying time before sanding.
Ensure you use fine-grit sandpaper and sand along the wood grain direction. Then, dust with a static rag before finishing with a tack cloth.
The primary reason for sanding between polyurethane layers is to smooth out dust nibs and eliminate other blemishes.
The process also helps to create a more robust mechanical bond with subsequent coats.
However, fast-drying and water-based polyurethane remain glossy even after sanding. Therefore, the exercise may not facilitate adhesion.
What Grit Sandpaper Between Paint Coats?
Sanding helps the coats adhere better and not distort the previous ones. Thus, please sand lightly to avoid leaving scratches.
Most projects need 320-grit sandpaper. But you can also use 400-grit or clogging sandpaper, which still gives a satisfactory result.
Alternatively, you can sand by hand for manageable applications. However, an electric sander will come in handy for large projects.
Also, the latter reduces your waiting time between paint coats.
What Type of Paint Should I Use Over a Polyurethane Finish?
Ideally, any paint type will work after you’ve deglossed, sanded, or primed the surface. Thus, feel free to choose any preferred product.
You have three options.
- Oil-based paints. They are the most durable but possess strong fumes and cure slowly. Hence, you need safety gear and a well-ventilated workspace.
- Latex Paint. This formula works best as wall paint. However, it is less durable and suits low-traffic areas or else you’ll keep touching it up.
In addition, latex paint has less odor and dries faster since it is a water-based product.
- Enamel Paint. The solution has the best of both worlds. For instance, it is durable, has fewer VOCs, and has a faster drying time.
You’ll likely try to keep up with the times as decor and design trends change. But your polyurethane varnish or lacquer may prevent easy or immediate decor changes.
However, do not despair, as the discussion above may just do the trick!
Can You Paint Over Polyurethane?
It is possible to paint over polyurethane. However, ensure that you prepare the surface properly.
Besides, the paint will not stick directly to the surface and will peel off eventually. Thus, you are sure of a durable project.