How to Spray Polyurethane | Steps + Must-Read Tips

spraying polyurethane over painted cabinet

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Did your project end up with uneven and undesirable poly finish? Or maybe you’re looking for a quick and easy process to give your DIY furniture a professional look? 

Try spray polyurethane and you might not apply poly with a paintbrush ever again! Read on for tips and everything you need about this spray method!

Can You Spray Polyurethane?

Yes, you can apply polyurethane with a spray gun. When spraying, polyurethane leaves a smooth finish free of brush strokes or roller marks. But not all polyurethanes are sprayable.

spray painting polyurethane

What is Polyurethane Used For?

You can protect DIY furniture with a layer of polyurethane because it is transparent and long-lasting. You can use it for the walls, ceilings, and trim around your windows, floors, and even your cabinets.

Can I Spray Oil-Based and Water-Based Polyurethane?

Spraying polyurethane yields a beautiful, glossy finish, but if you choose the wrong kind, you could end up with an unsatisfactory appearance. While both types of polyurethane serve the same purpose, water-based and oil-based varieties each have their quirks that should be considered.

Differences Between Water-Based and Oil-Based Polyurethane

#1: Color and Appearance

The most obvious difference is in appearance. Polyurethane spray with a water base looks milky in the can, while oil-based poly looks yellow. Oil-based polyurethane takes on a dark amber color when it dries.

However, water-based polyurethane dries transparent and keeps that quality for the duration of its useful life.

filling sprayer with polyurethane varnish

Oil-based poly is great if you want deeper, more vibrant colors. But, only water-based will do if you want the wood’s natural hue preserved.

#2: Drying Time

Spraying polyurethane instead of brushing or rolling helps speed up the drying process, but waiting for oil-based polyurethane to dry can be excruciating. It takes about 5-12 hours for oil-based polyurethane to dry before the second and third coats.

In ideal conditions, another spray coat can be applied to water-based polyurethane in as little as two hours. The quickest time is 4 hours, with fast-drying oil-based ones.

#3: Difficulty of Cleaning

You also must consider how simple or complicated it is to clean your tools after use. You can dilute and wash away water-based polyurethane spray with gun cleaning solvent.

sprayer and mineral spirits

Mineral spirits are used to dilute oil-based polyurethane and as a solvent to remove any residue. This is the same method used to clean an oil-based polyurethane brush. As might be anticipated, this is more time-consuming and challenging.

#4: Toxicity Level and VOC Content

Spray polyurethanes are toxic in general. They contain isocyanates and release VOCs [1] into the air. When sprayed, this toxicity is amplified.

Both types of polyurethane release volatile organic compounds, but oil-based polyurethane releases far more. That’s because more VOC-containing chemicals are required to produce oil-based polyurethane.

#5: Price

While water-based polyurethane is more costly, it speeds up the process and requires less expensive cleaning materials.

mixing polyurethane for air sprayer

How to Spray Polyurethane in 10 Easy Steps

Tools and Materials You’ll Need to Spray Polyurethane

Step #1: Don Protective Equipment

To avoid harm from polyurethane, you have to at least dress in layers. When working with polyurethane, it’s important to wear protective gear to avoid getting the toxic volatile organic compounds (VOCs) and isocyanates in your eyes, nose, or mouth.

person wearing protective gear while spray painting

Step #2: Prep the Poly

To get the polyurethane ready, you just need to do these three things:

Step #3: Set Up Your Workspace

Polyurethane finishes are difficult to keep from spreading when spraying, so they often do. To prevent spray from damaging other items in your workshop, lay down a drop cloth.

spraying polyurethane to cabinet doors

In addition, you should open the windows a little to let in some fresh air. Put the fan in the opposite direction or turn it off if it blows in your direction.

Step #4: Clear the Surface From Dust

Sand the wood down before you start working on it. To remove all traces of dust from the wood after sanding, use a vacuum or a tack cloth.

Although bubbles are unlikely when using a spray, dust nibs can still be left behind if you don’t take your time.

To prevent dust from being blown onto your work by the fan or outside air, you should also clean any potential dust collectors in the immediate area.

Step #5: Test the Sprayer

Once you have achieved a consistent flow, try it out on a small section of the wood. This is crucial, as the aesthetic appeal to you could make or break the deal.

testing sprayer

Wood finished with oil-based polyurethane will take on an amber hue. Water-based polyurethane, despite drying crystal clear, can still result in discoloration or yellowing when sprayed on white-painted surfaces, so testing is advised.

Step #6: Spray the Polyurethane

Spray Pattern

The three different spray patterns on a polyurethane sprayer allow it to be used on various surfaces. Some examples of possible applications for the spray patterns are provided below.

Horizontal Spray

Applicable when spraying doors, cabinet sides, and fronts, among other vertical surfaces. You can use this method on vertical surfaces, and the spray pattern will either move from right to left or left to right.

Vertical Spray

This spray pattern is designed for use on flat surfaces such as tables. Thus, the design is a spray that moves both vertically and horizontally.

spraying polyurethane over painted cabinet

Step #7: Allow the Wood to Dry

The water-based polyurethane is slower to dry than competing brands. Unfortunately, no other spirits or solvents will hasten the drying process. Heating the surface or increasing airflow is the most effective way to quicken the drying.

Step #8: Sand the Wood

Polyurethane spray paint needs two to four hours to dry before you can reapply polyurethane over the paint. When dry, use 220-grit sandpaper to smooth out any bumps, divots, or runs.

If you sand the wood, be sure to go with the grain. Don’t dig too deeply; you want to leave just enough roughness for the subsequent coat to adhere.

Step #9: Clear the Surface From Dust Again

Take out the vacuum or tack cloth once more after you’re done sanding. You’ll need to be patient because there will still be dust in the air, even after spraying it.

cleaning surfaces with cloth

When cleaning, be thorough and aim for any cracks or crevices where dust could be hiding.

Step #10: Spray Another Coat

To apply the second coat, follow the same procedure as before. Make sure the spray is still effective by first using it on an unfinished wood surface.

Following the completion of the second coat, repeat steps 6–9 until the desired finish is achieved. Achieving a smooth finish typically requires three or four coats.

spraying polyurethane

When finished, wait for the polyurethane coating to cure before fully putting any weight on it. This would take about 3 weeks for water-based polyurethanes, and for oil-based polyurethanes, it would take about 4 weeks.

Must-Know Tips for Spraying Polyurethane

Best Sprayer for Polyurethane: Top Picks

1. HomeRight C800971 - Top Choice for Water-Based Polyurethane

HomeRight C800971

The three brass spray tips are reliable, and they are resistant to wear and corrosion as well. In addition, it uses only 450W of power, making it ideal for even the most intensive of projects.

The air cap can shoot out in a spherical, horizontal, or vertical pattern. You can also use this on milk paint and chalk paint.

What We Like

What We Don't Like

2. YATTICH Paint Sprayer - Top Choice for Oil-Based Polyurethane

YATTICH Paint Sprayer

This sprayer has five copper nozzles and can be used on various poly finishes and surfaces. It has three distinct spray patterns: vertical, horizontal, and circular. The amount of liquid released can be adjusted by turning the volume knob.

With this product, you get everything you need to do the job, including a viscosity cup, a cleaning needle, a brush, a spanner, and a pot with a lid.

What We Like

What We Don't Like

Spray Polyurethane vs. Brush: Which is Better?

When working on a flat surface, spraying is the most efficient method because it covers the entire surface in a single pass.

polyurethane varnish on wood

Using a brush allows you to reach into crevices and around edges more easily when working on a project with a curved or angular surface, such as table legs.

Drawbacks of Applying Polyurethane with a Brush

Undesirable Finish

Polyurethane application must take place in a dust-free setting, or you’ll get undesirable results. Air bubbles are common problem with polyurethane when you’re in a dusty room. The surface will be uneven if you let bubbles dry in your finish. Sanding the bubbles is the only solution.

Tricky Application

Brushing on polyurethane can be tricky. Long, even strokes should be used when brushing poly. In addition, you should always maintain a wet edge. 

applying polyurethane varnish on a door

Brushing over an area where the poly is dry or just drying will cause you to pull the finish, resulting in bumps when it is completely dry. It will be necessary to sand down these humps before the finish can be applied.

Does Not Give the Best Look on Wood

When applied with a brush, poly can take on a plastic-like appearance despite providing a clear, durable finish. 

The polyurethane doesn’t allow the wood to absorb it. If you look closely, you can see that it floats on top of the ground.

Is Spraying Polyurethane Toxic or Safe?

There is no doubt that the VOCs released during the spraying of polyurethane can be harmful to human health. 

lady spraying cabinet with polyurethane

This is why always wearing protective gear when working with polyurethane is important. Once polyurethane has dried, its toxic effects will cease.

Do You Need to Thin Polyurethane Before You Spray?

Polyurethane does not need to be diluted before spraying. Thinning, on the other hand, can help you achieve a more uniform look and feel.

Thin water-based polyurethane with water and mineral spirit or paint thinner for oil-based poly. Test before applying it all over.

Is it a Requirement to Sand in Between Polyurethane Coats?

It is not necessary to sand in between spray coats of polyurethane. All manufacturers or products do not require sanding, but keeping the habit is a good idea.

sanding table with polyurethane coat

Dust nibs and uneven application can be removed by sanding between poly coats. The surface is made slightly rougher after sanding, which aids in the adhesion of the subsequent polyurethane coat.

FAQ

Is spray polyurethane any good?

Spray polyurethane is good. All wood surfaces benefit from being coated with polyurethane spray. This coating is long-lasting, attractive, and sturdy. Using a spray gun to apply polyurethane will produce excellent results.

What's the best way to spray polyurethane?

The best way to spray polyurethane is to focus on applying as thin layers as possible. Keep the sprayer 10 to 12 inches from the surface to avoid uneven coating and bumps. When spraying, a steady, even stream is ideal. 

Can I spray Minwax polyurethane products?

Some Minwax products, including Minwax fast-drying polyurethane, are sprayable. Some of Minwax’s polyurethane sprays are oil-based, while others are water-based.

There is no need for a paint sprayer with Minwax’s aerosol polyurethane; it achieves the same results.

Is there a better way to apply poly?

Use a fine paintbrush, foam pad, or cloth to spread a thin layer of polyurethane over the surface. It’s important to go with the grain and not use too much polyurethane, which can cause the wood to warp. After a couple of hours, the first coat should be dry enough to apply a second.

Conclusion

Spraying polyurethane is the quickest way to apply it, excluding cleanup and drying time. Follow our instructions on how to spray polyurethane to achieve a buttery smooth finish without the hassle of a foam brush or roller.

In addition, it’s a snap to apply and provides a polished finish for your do-it-yourself furniture projects.

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen and women. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
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