How to Spray Polyurethane Paint

Despite its fantastic utility, polyurethane brings dread to those who lack experience in DIY projects. Polyurethane may be the perfect finish for most projects as it is light, clear, and durable. However, it is also unbelievably finicky.

Most will try to apply polyurethane with a paintbrush, making the delicate finish all the more difficult to use. Stirring and wiping the rim with the brush creates bubbles that can ruin a whole batch.

Brushing along the surface has to be done with absolute precision lest you leave bumps and grooves behind. Faulty brushing combined with humidity can trap moisture and leave the finish cloudy or white. The list goes on.

However, one simple change can make polyurethane a much more consistent and successful experience.

Spraying polyurethane with a paint sprayer takes out the most volatile variable and makes the entire project far less reliant on your skills as a painter.

Spraying polyurethane requires a few extra steps to ensure quality but the added effort will leave you with a better-looking finish and less time spent fixing mistakes.

The following article is a step-by-step guide for the best way to spray polyurethane finishes.

We will go through the preparations and applications steps to ensure you never have to worry about polyurethane ever again.

Preparation the Paint & Spray Gun

1. The Piece

Prepping the project is no less essential than the application itself. First, get your piece ready for a finishing coat by sanding it evenly and filling in any undesired holes and gaps. Then apply a stain and allow it dry.

While it’s drying, you will want to make sure that the polyurethane is applied in a dust-free environment. Using a spray tent is the most effective way to keep dust out of the finish while also protecting surrounding objects.

It is also an ideal drying space that isn’t likely to be compromised. However, a workshop can also be cleaned and vacuumed thoroughly.

2. The Sprayer

Get the prayer ready for the project by first selecting the proper spray tip. A tip that sprays between 1”-6” wide is ideal for spraying polyurethane and other finishes. Most airless sprayers will come with a few selections, otherwise extra tips and be found at hardware stores and online.

Next, you will need to adjust the volume control knob. This part can be tricky because you want to get to a place where you are spraying just enough polyurethane to create an even coating with each pass over.

Too much will drench your project while too little will leave you with an uneven surface. Almost all airless sprayers worth their salt will have a pressure control feature.

Play with it a little and practice before starting the project.

3. The Polyurethane Paint

Before you fill up your sprayer’s tank with pure polyurethane, remember to prime a project beforehand. A priming mixture for polyurethane is simply a 2 to 1 ratio of polyurethane to paint thinner. Add the polyurethane to the container and then add half that amount of paint thinner.

After this first layer of primer is applied then additional, pure coats can be added.

Spraying Polyurethane

Though it is certainly more effective than brushing, spraying polyurethane requires a specific technique that is easy to master.

You will want to begin by keeping the sprayer at least 10” to 12” away from the surface, this will make sure the coat remains even without globs or bumps.

As you spray, you will want to have a long continuous flow. Stopping mid-spray results in an uneven application that will be hard to fix later.

With every layer then, spray until you have covered the area and then stop. You can use a system by beginning the spray just before it hits the surface, carefully drawing the sprayer across the area and stopping after you have passed beyond the piece.

You will want to keep your wrist stiff and steady throughout the process. It can be tempting to bend and wave as you spray but you will form arcs of uneven coats instead of an even straight line.

One of the keys to how to spray polyurethane is knowing which setting to use for different parts of the project. Again, most good sprayers will come with various settings and setups that can be quickly adjusted.

Use the vertical setting to spray up and down table legs, pegs, and columns. The horizontal setting is perfect for moving across an area while the middle setting (sometimes called horizontal/vertical or circular) is ideal for corners, edges, and nuanced curves.

The Trick to Layering It

Between each coat of polyurethane, you will need to let it dry and then give it a light sanding. Polyurethane will not stick to itself unless the wet layer has grooves and scratches to latch onto. A very light hand with 220 grit sandpaper will do the trick.

Remember, the key is not to actually remove the dry layer but to make the surface rough so the next layer can grip it.

After sanding, you will want to make doubly sure that there is no dust left on the surface or around the piece. Use a strong shop vacuum and meticulously clean every inch before applying another layer.

Without this step, your next coating will be polluted with dust. What should be a clear finish, will appear cloudy and opaque.

After 3 coats, your project should have the perfect look and feel.

Overall

Spraying polyurethane is undeniably easier. After a little practice and adjustment, you should be applying every coat with ease. Paint sprayers for polyurethane are widely available on Amazon and can be as cheap as $50 when using simple DIY paint sprayers for furniture.

More expensive models will come with more features and better components, but you won’t need to invest an arm and a leg to get started.

Most standard paint sprayers can be used for polyurethane finishes as long as they are thoroughly cleaned between projects. The results of an airless sprayer are second to none in terms of quality.

Never again will you have to worry about brush strokes or stirring mistakes. You will have a beautiful, professional finish with little effort and in half the time.