How to Spray Polyurethane? (5 Steps)

Spraying paint has always been better and faster than using a paintbrush. But how do you spray polyurethane?

To spray polyurethane, you would need a paint sprayer or a spray gun. Both painting equipments are designed with chambers where you can load the polyurethane paint and nozzles where the polyurethane can come out from when the trigger is pulled. You can also purchase spray-on polyurethane paints.

The spray-on polyurethane paint comes in a spray can so you can easily spray it with very little prep work. However, you should know that not all types of polyurethane can be sprayed due to their different features.

So what type of polyurethane can you spray and what type shouldn’t you spray? Also, at what pressure should you spray polyurethane? The answers to these questions and more will be revealed in this article. So let’s dive in.

Can You Spray Polyurethane?

You can spray polyurethane by using a spray gun, an airless paint sprayer, or a compressed paint sprayer. All of these are painting equipment that are designed with a paint cup. You can pour the polyurethane into the paint cup and pull the trigger to spray the polyurethane through the nozzle of the spray gun.

However, there are a few things to know before you spray polyurethane:

  • It’s generally advised to thin polyurethane before spraying – Polyurethane is usually very thick and in its thick state, it would be difficult to get it flowing through the nozzle of the spray gun. So thinning the polyurethane before spraying makes it light enough to flow through the nozzle easily.
  1. Spray-on polyurethane is a better choice for people that wants to spray polyurethane. This is because you don’t need to thin or stir spray-on polyurethane. In most cases, you just need to shake the can for a few seconds.
  1. Not All Types Of Polyurethane Should Be Sprayed – Many sources might tell you that you can’t spray some types of polyurethane. This is false. All types of liquid can be sprayed if thin enough. So as long as the polyurethane is thin enough to flow through the nozzle, you can spray it but you shouldn’t spray all types of polyurethane. The reason not to spray all types is that there are different types of polyurethane.

Oil-based polyurethane for instance is very thick. To spray oil-based polyurethane, you’ll have to heavily thin the polyurethane to make it light enough to flow through the nozzle of the spray gun. Thinning the paint that heavily can make it lose its natural glossy and hard finish which means it won’t protect your wood.

Should You Spray Oil-Based Polyurethane or Water-Based Polyurethane?

Should You Spray Oil-Based Polyurethane or Water-Based Polyurethane?

You can spray water-based and oil-based polyurethane but you should know that water-based polyurethane is easier to spray than oil-based polyurethane.

This is why it’s generally recommended not to spray oil-based polyurethane. To know why water-based polyurethane is easier to spray, let’s do a quick comparison between the two types of polyurethane; oil-based vs water-based polyurethane:

Paint Flow

The paint flow is the most important factor to consider when picking polyurethane to be sprayed. This is because the flow determines if the polyurethane would spray easily or not. Water-based polyurethane has a thin flow. Water-based polyurethane uses water as the solvent so the particles are usually light or thin.

Oil-based polyurethane however has a thick flow. This is because the particles are usually dissolved in oil. Since oil is thicker than water, oil-based polyurethane will have a thicker flow than water-based polyurethane. As such, water-based polyurethane is easier to spray.

Paint Thinner

Regardless of the type of polyurethane, it’s always recommended to thin the polyurethane before spraying. It’s easier to thin water-based polyurethane than oil-based polyurethane.

This is because water-based polyurethane can be thinned easily with water. Oil-based polyurethane however requires a mineral or petroleum-based solvent like mineral spirits to be thinned.

Due to the thick nature of oil-based polyurethane, you’ll also need to thin it with a lot of paint thinner to make it flow through the nozzle. This on its own can be risky as thinning polyurethane heavily can take away its natural and glossy finish.

Toxicity

Water-based polyurethane has a very low toxicity level when spraying. This is because it contains no harmful chemicals or solvents. Since water-based polyurethane can also be thinned with water, you are at less risk of toxic chemicals. So water-based polyurethane is safe to spray.

Oil-based polyurethane on the other hand is known to contain paint chemicals and solvents. Since you also need to thin oil-based polyurethane with a solvent, this increases the chemical and solvent level in the paint.

So if you spray both types of polyurethane after thinning, the toxicity level that you will be exposed to will be greater while spraying oil-based polyurethane. This is why it’s advised to spray in a well-ventilated space.

So in summary, water-based polyurethane is easier and safer to spray than oil-based polyurethane.

Related Read: Oil-Based vs Water-Based Polyurethane?

What Pressure Are You To Spray Polyurethane?

You are to spray polyurethane at a pressure of 28 PSI. Generally, clear coats like polyurethane should be applied with the spray gun pressure set between 26 and 29 PSI. At this pressure, the polyurethane can be well atomized (or sprayed) on the surface.

If the pressure is lower than 25 PSI, then the polyurethane will not be expelled smoothly from the nozzle. Since the paint is thicker, more pressure is required to expel it smoothly on the surface.

Now you know the right pressure to spray polyurethane. But the pressure is just one of the things to know when you want to spray polyurethane. So for the next part of this article, let’s find out how to spray polyurethane.

How To Spray Polyurethane? (In 5 Simple Steps)

To spray polyurethane effectively, you’ll need a few tools and supplies:

  • Clean rags
  • Sanding sealer (for if the surface is bad or rough)
  • Sandpaper
  • Paint sprayer or spray gun
  • Spray shield
  • A pair of gloves
  • A face mask
  • Drop sheets
  • Painter’s tape
  • Mineral spirits or paint thinner

Here is a 5-step guide on how to apply polyurethane:

1. Prep Your Workspace

Prep Your Workspace

The first step before spraying polyurethane is to prep your workspace. You should start by putting a large drop sheet on the floor to prevent polyurethane from staining the floor. You can hold the drop sheet down on the floor with painter’s tape so it doesn’t move out of place while spraying.

You should also use painter’s tape to demarcate areas that you don’t want the polyurethane on. A part of prep work is to put on a pair of gloves and breathing protection so you don’t handle or inhale paint chemicals.

As a part of prep work, you should apply a coat of sanding sealer over the surface especially if the surface is rough or uneven. The sanding sealer will help to condition the surface so the polyurethane is applied smoothly and evenly.

2. Sand The Surface

Sand The Surface

After enough prep work, you should sand the surface. Sanding helps to smoothen the surface so the polyurethane can go on smoothly.

If you applied sanding sealer, you also need to sand down the sealer coating to allow the polyurethane to stick. You should only sand with fine-grit sandpaper.

3. Thin The Polyurethane

Thin The Polyurethane

The next step is to thin the polyurethane. As explained earlier, this helps the polyurethane to flow easily through the nozzle of the spray gun. You should thin water-based polyurethane with water or an alcohol-based solvent. While oil-based polyurethane should be thinned with mineral spirits or lacquer thinner.

You should never switch paint thinners. This means you should not use water to thin oil-based polyurethane or thin water-based polyurethane with mineral spirits. Doing so will ruin the color, consistency, and flow of the polyurethane.

You should thin the polyurethane in the ratio of 4:1 (4-part polyurethane to 1-part paint thinner). At this level, the polyurethane will flow better and still maintain its hard and moisture-resistant finish.

4. Prep The Paint Sprayer

Prep The Paint Sprayer

You should prep the paint sprayer based on the user’s guide or manual. Usually, you’ll first need to clean and wipe the sprayer. Then you’ll need to pick the right key or tip to attach to the paint sprayer. For polyurethane, you can use a tip between 1.0 and 1.5mm.

You’ll also need to prime the sprayer. To do this, you’ll need to pour the polyurethane into the paint sprayer and switch the multiport valve to prime. When you see polyurethane paint flowing out through the nozzle, the paint sprayer is fully prepped and ready to go.

If you are using the spray-on polyurethane, you don’t need to prep any sprayer. All you have to do is shake the spray can gently for a few seconds. Doing so will mix and stir the polyurethane in the can.

5. Spray the Polyurethane

Spray the Polyurethane

The final step is to apply the polyurethane. But before you do this, you should test the sprayer first to see if it goes on smoothly and dries well. While spraying the polyurethane, ensure to cover the area with overlapping sprays. Also, ensure to leave about 10 inches between the nozzle of the sprayer and the surface to prevent splashes.

You only need 2-3 coats of polyurethane for proper coverage. You should allow each coat to dry for at least 3 hours before recoating. You should also sand between each coat of polyurethane with 320-grit sandpaper. The final coat doesn’t need sanding. Ensure to let the polyurethane dry for at least 3 days before the surface is used or wiped with a solvent.

Does Polyurethane Work Well?

Polyurethane is a great finish and it works well on different types of surfaces including wood. Polyurethane offers moisture resistance and scratch resistance. Some types of polyurethane like exterior polyurethane even offer weather and UV resistance to the wood. The features of a polyurethane finish make it work well.

Polyurethane is one of the strongest and best finishes in the painting world. The word “urethane” is a plastic-like material that dries hard. When the polyurethane dries, the liquid layer becomes a very hard and moisture-resistant finish.

The hard layer prevents scratch marks, scars, claw marks, and dents from reaching the surface underneath. The hard layer also prevents moisture and solvents from penetrating. Having polyurethane over a surface is like having a shield over the surface. So if you are having any doubts about polyurethane, be rest assured because polyurethane works well.

Is Spray Polyurethane Better Than Brush-On Polyurethane?

Spray polyurethane is considered better than brush-on polyurethane because spray polyurethane is easier to apply and it gives a better finish than brush-on polyurethane.

Spray polyurethane can also be used by beginners as spray polyurethane is hard to mess up. Brush-on polyurethane on the other hand will reveal brush marks and strokes if applied by an inexperienced person.

Here are other reasons spray polyurethane is considered better than brush-on polyurethane.

  1. Spraying polyurethane offers better coverage over the surface
  2. Spray polyurethane doesn’t require much prep work while brush-on polyurethane should be thinned, stirred, and left to settle.
  3. Spray polyurethane covers more quickly than brush-on polyurethane so you can apply the paint faster
  4. Spray polyurethane covers the surface evenly
  5. Brush-on polyurethane reveals brush marks but spray polyurethane goes on smoothly
  6. Spray polyurethane is easier to apply
  7. The finish is usually better than brush-on polyurethane.

You should know that brush-on polyurethane is not a bad choice. In the hands of experienced painters, you’ll get the same type of result as spraying the polyurethane.

Final Words

In summary, polyurethane can be sprayed. You just need to pick the right type of polyurethane for spraying. You should also check the pressure gauge and the key (or nozzle) to ensure it’s the right setting for spraying a clear coat like polyurethane. Finally, ensure to apply the paint in a well-ventilated environment to prevent a build-up of paint fumes.

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