How to Spray Polyurethane: 9 Steps to Get a Perfect Finish!

Are you thinking of the best way to apply that polyurethane finish on your furniture without having to deal with irregular lines, bumps, and imperfections on the wall?

If yes, then you are in the right place. This post will introduce you to and explain all you need to know about how to spray polyurethane as well as an expert.

So stick around as we take another fascinating dive into the world of painting.

What Is Polyurethane and What Is It Used for?

Polyurethane is a type of varnish finish that is used on furniture, doors, wooden slabs, wooden frames, and floors because of its increased durability and splendor. The product gives a strong coat that makes the surface brighter, more beautiful, scratch-resistant, durable, and much more weather-friendly.

The coat also creates a glossy finish that makes the surface light-up under direct rays of light.  But before your surfaces can get all that durability and beauty, you need to apply the polyurethane to the surface and that’s where the problem lies.

Can I Apply Polyurethane With a Paintbrush?

The direct answer is yes. You can apply polyurethane on a surface using a paintbrush but it is not advised particularly if you have no prior experience with undertaking such a task.

Unlike most paints and finishes that can be applied using a paintbrush, polyurethane doesn’t come out well when applied with a paintbrush especially by a beginner or a DIYer.

This is because polyurethane needs to be applied smoothly and using a paintbrush will most likely leave you with brush strokes and stripes on the surface when the paint cures (or dries).

Not to mention the possibility of having irregular layers of paint too since polyurethane doesn’t stick to itself as well as other finishes.

Overall, the finish you get after using a paintbrush will most likely be uneven and riddled with bumps. This makes the surface ugly and rough which I’m sure is not what you are going for. So if you shouldn’t use a paintbrush..

What Is the Best Way to Apply Polyurethane on a Surface?

Well, that would be by using a paint sprayer. Paint sprayers are fast and highly efficient painting equipment. Paint sprayers make it possible, convenient, and very easy to spray multiple layers of finish on any surface within seconds.

So it’s no surprise that it is the best way to apply polyurethane. But that’s not all. What tools do you need to spray polyurethane? Should you sand before spraying polyurethane?

You see there is more to know about spraying polyurethane. So like Shakespeare once said, let’s get spraying. LOL, I’m just kidding, Shakespeare never said that.

What Are the Tools Needed to Spray Polyurethane?

  • Pair of Work Gloves
  • Respiratory Mask
  • Pair of Goggles
  • A Bucket of the Polyurethane Finish – Polyurethane finish comes in two variations. There is water-based polyurethane and oil-based polyurethane. Individually, both variations are great. You should get the one that best suits your taste and would go well on the surface you want to paint.
  • Paint Sprayer
  • Clean Rags
  • 1 x Drop Cloth
  • Duct Tape
  • Warm Water
  • Sandpaper

How to Spray Polyurethane?

Spraying polyurethane paint is a task that requires you to take extra caution and to follow all the instructions stated on the container of the finish.

Spraying polyurethane takes a lot of time. You have to be careful while doing it because it can easily destroy your whole project. But, if you do it correctly, your furniture/surface will look better and the paint will last longer.

The slightest bit of error on your part can lead to long-lasting flaws on the painted surface. From personal experience, I know how difficult it can be to spray paint polyurethane but do not worry.

The steps below have been carefully drafted and well explained to make the entire process easier. Stick to the steps below and you will be spray painting polyurethane like a pro in no time.

Put on Your Safety Gear

Before embarking on any painting task, you should ensure to protect your eyes, skin, and lungs. As beautiful as polyurethane finish is, it is not meant to be used on the body and it sure isn’t meant to be inhaled in the lungs either.

Even the water-based polyurethane contains resins which if inhaled can cause problems. Also, allowing the paint to come in contact with your skin can cause health concerns. So, safety first.

Prep Your Workspace and Surface

To achieve the best finish possible, you should take some time to prep the workspace and the surface you want to finish. This may take you a few minutes or a few hours depending on how large the surface is and the condition of the workspace.

Firstly, you should remove any object, furniture, or electronic device near the workspace. If there is any object you wouldn’t want polyurethane to get on, you should move it out of the room or cover it with a thick drop cloth or a water-resistant cover like a plastic sheen.

After removing and covering all objects nearby, you should go ahead to tape all trims and edges. The window trims, door frames, baseboard, molding, and the likes should be covered with duct tape to prevent the polyurethane from dropping or splashing on them. If you have any wall outlet or object on the wall you want to finish, you should remove them too. Then cover your floor with a big drop cloth.

You can tape the drop cloth to prevent it from exposing the floor. While working, you will step on and move around on the drop cloth. If the drop cloth isn’t firmly taped down, it would wrinkle and expose the floor it should be protecting and we don’t want that.

Sand the Surface

Yes, you should sand the surface you want to finish before spraying the polyurethane. Without sanding, you will end up wasting your time and the polyurethane.

You can start with coarse sandpaper and then move on to fine sandpaper. Remember not to use aggressive sandpaper. What you are trying to do is to increase the adhesiveness of the wall so the finish can stick to the surface properly.

Any sandpaper between 80-grit to 120-grit should suffice for a start. Rub the sandpaper against the surface in a circular motion for a while. You can also attach the sandpaper to a sander or an angle grinder to make the task easier. After sanding, wipe off the sanded debris on the surface with a clean rag or a soft brush.

Thin and Mix the Polyurethane

Not every polyurethane product needs to be thinned. There are many polyurethane products out there in the market that can be used directly from the paint container.

You just need to mix it to ensure there isn’t any lump in the paint. If you have that type of polyurethane, then you can skip the thinning process. However, if you don’t, you will need to thin the polyurethane. To know if you need to thin the polyurethane or not, you should check the container for the guidelines on how to use the product.

Most polyurethane products need to be thinned and carefully mixed so the finish can flow on the surface smoothly. To thin oil-based polyurethane, you should use paint thinner. For water-based polyurethane, you should use water.

After thinning, you should carefully mix the paint so it is smooth and without lumps. While mixing the paint, you should do so gently. If you mix the paint aggressively or turn it quickly, you will cause a build-up of air bubbles in the paint container and that will just make the whole process more tedious.

Prep the Paint Sprayer

Since you would be spraying the paint, you need to prep the paint sprayer. Prepping the paint sprayer includes picking the right tip, cleaning the sprayer, and priming the pump of the sprayer. Don’t worry, these are very easy to do.

For the right tip, you should pick one between 013-015. The number is usually inscribed on the tip so you can identify it. Some paint sprayers come with colored tips. The one for polyurethane is usually painted blue but you should still consult the paint sprayer manual for a recommendation on the right tip to use.

Prime the Pump

To prime, unplug the cord of the sprayer and ensure the trigger is locked so you don’t pull it accidentally. Then put the suction tube inside the paint and get an empty bucket or bowl for the return tube and put the return tube inside.

Then switch the prime and spray knob to the prime position. The knob is usually made of plastic and painted black. You will see the words spray and prime written on it. Simply turn the knob to the prime position and plug in the paint sprayer.

Once you have done that, turn the pressure knob on the side of the spray gun and start with low pressure. When you see the paint flowing, that means you have primed the pump of the sprayer. Switch off the machine and submerge the return tube into the paint too.

The return tube returns the left-off polyurethane into the paint bucket to prevent wastage. Once that has been done, you can switch the prime and spray knob to spray.

You should also adjust the volume of the sprayer. The volume controls how much paint flows through the tip. Make sure the volume isn’t too high as that will just cause the paint to drip off the wall. The volume should not be too low either.

If it’s too low, not enough paint will flow through the tip.  When you have selected the right tip, primed the pump, and set the volume, you are ready to go ahead. But you shouldn’t spray just yet.

Related Read — Oil vs. Water-Based Stain

Test the Sprayer or Spray Gun

After successfully prepping the sprayer, you need to test it out to be sure you have the desired volume of spray. Remember, we don’t want too much or too low spray so it’s only proper to test it out.

To test the sprayer, plug-in the cord and switch on the sprayer. Then aim the nozzle at a dispensable board, cloth, or furniture.

Pull the trigger and check the flow of the paint. If you are satisfied, you can go ahead to spray the main surface. If you aren’t, you can adjust the volume of the sprayer.

Related Read — How to Thin Latex Paint?

Spray the Polyurethane

Finally, the step you have been waiting for. After testing the spray level of the sprayer, you can go ahead to spray the polyurethane on the surface.

The first thing to do is to select a spray pattern. Most paint sprayers have a knob at the rear of the spray gun to control the spray pattern. The knob might be positioned in another part of your sprayer so consult the manual.

If you are trying to spray a broad surface like a tabletop or a wall, you should use the horizontal spray pattern. For vertical surfaces like poles, you should use the vertical spray pattern.

While spraying, there are a few things you should take note of. Firstly, do not move your wrist. You should always keep your arm straight while spraying.

Do not at any point bend your wrist. Your arm should be straight and firm. Then move your arm from left to right while spraying overlapping layers of polyurethane. If you move your wrist, you will end up with more polyurethane on one part of the surface than others.

Also, keep at least 10 inches between the nozzle of the spray gun and the surface you are painting. If you move the nozzle too close to the surface, you wouldn’t cover much of the surface in time and you will also have the polyurethane concentrated on one part of the surface leading to drips and runs.  If you move too far away, you will end up wasting paint as the polyurethane finish wouldn’t get to the surface well.

You should also overlap each layer of polyurethane with another. You might need up to 3 layers of coat for a nice glossy finish. Finally, you should always wear a mask and a pair of goggles while spraying for protection.

Clean Up the Equipment and the Workspace

After completely spraying the polyurethane, clean up the equipment and the workspace. You can use paint thinner to remove paint from the paint sprayer.

If you leave any paint in the sprayer, it will block the nozzle and that will shorten the lifespan of your paint sprayer. Also, remove the drop cloth that was used to cover the furniture and floors. Then clean the workspace.

Pro Tips to Follow While Spraying Polyurethane

  • DO NOT spray polyurethane if the weather is windy. A major downside of polyurethane is that it shouldn’t be used outdoors or in a dusty environment. The product attracts a lot of dust while it is drying and wet paint and dust don’t go well together. The dust will affect the smoothness of the final finish. If you must spray and you suspect dust might hamper the finish of your task, you should buy a spray shelter.

Spray shelters make it possible to spray in harsh weather and dusty conditions. Think of a spray shelter like a tent. Only that this tent isn’t used for camping outdoors. It is used for spraying effectively in harsh weather and dusty environment.

  • Start spraying before you get to the surface and stop spraying after you have completed that lap. This means you should pull the trigger before you get to the surface and release the trigger after you have completed a lap at the end of the surface. If you start spraying right on the surface and stop at the other end, you will have imperfections at both ends of the sprayed surface.
  • Always clean the sprayer and other equipment immediately after use. If you don’t, the paint will get dry and clog the nozzle of the paint sprayer making it very difficult to use it effectively next time.
  • Always keep tabs on the equipment while spraying. While spraying, you should pause for some time to inspect the paint sprayer. This helps you prevent any uh-oh moment while spraying.
  • Always wear a mask, a pair of goggles, and thick clothing to protect yourself even if you are using water-based polyurethane. Water-based polyurethane still contains resins and other chemicals that can be very harmful if introduced into the body system.

Expert Tip for Polyurethane to Stick Better

Polyurethane isn’t the stickiest of finishes. This is why professional painters advise DIYers to sand and use products that can increase the adhesiveness of the surface to be painted so a smooth finish can be achieved.

As an expert tip, you can also sand between each coat of polyurethane. After spraying the first coat, let it get dry and then sand. Use fine-grit sandpaper like the 220-grit or 240-grit to sand the first layer gently. You don’t need to use force as that will just damage the first coat.

What you are trying to do is increase the adhesiveness of the surface so the next coat can stick well to the surface without dripping.

So use fine sandpaper to lightly scrub the first coat for a few seconds. Then use a clean rag or a light brush to clean off any sanded residue. When that is done, you can spray another coat of polyurethane on the surface and it will stick just fine.

You can do this after the first and second coat so the third coat sticks like glue. Eventually, you will have a very smooth and fine finish.

So there you have it. Follow the steps and tips above and you are sure to have a fine polyurethane finish. If you have any comments or questions, you can leave them below and I’ll respond to them as soon as possible. Have a nice painting experience.

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