How to Spray Polyurethane? (5 Steps)

Spraying paint has always been better and faster than using a paintbrush. So, how to spray it?

To spray polyurethane, you need to thin it with water or mineral spirits, fill the sprayer, and spray it. You shouldn’t over-thin polyurethane as it can cause it to lose its glossy finish. 

You can also use spray-on polyurethane which comes in a bottle, so you can use it without prep work

Can You Spray Polyurethane?

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

Here are a few things you should know:

1. You Must Thin It – Polyurethane is thick, and in its thick state, it would be difficult to get it flowing through the nozzle. So, you must thin it to make it light enough so it can flow through the nozzle.
2. Spray-on polyurethane is better – This is because you don’t need to thin it. In most cases, you just need to shake the can for a few seconds.
3. You can’t spray all types – Technically, if you thin it enough, you can spray all types. But, oil-based polyurethane is thick, and if you heavily thin it, it will lose its natural gloss and hard finish and won’t protect a surface.

Oil-based vs Water-based Polyurethane (For Spraying)

You can spray both, but water-based poly is easier to spray.

Here is why:

Paint Flow

The paint flow is the most important factor when picking a polyurethane to spray because it determines if you can do it or not.

Water-based polyurethane has a thin flow because it uses water as its solvent, so the paint particles are light or thin. On the other hand, oil-based polyurethane has a thick flow because it uses oil as its solvent. Since oil is thicker than water, the oil-based type will have a thicker flow and is harder to spray.

Paint Thinner

Regardless of the type, you must always thin it before spraying. It’s easier to thin water-based polyurethane because you can use water. But, to thin oil-based poly you need to use a lot of mineral spirits. Plus over-thinning it can take away its natural and glossy finish.

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

How To Spray Polyurethane?

Here are the tools you need:

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

1. Prep Your Workspace

Put a large drop sheet on the floor to prevent splashes. You can hold the drop sheet down on the floor using painter’s tape so it doesn’t move out of place.

2. Sand The Surface

If the surface is rough or uneven, you must apply sanding sealer over the surface. The sanding sealer will condition the surface so the sealant is applied smoothly and evenly. 

After you apply the sanding sealer, you must sand the surface with fine-grit sandpaper. Sanding will smoothen the surface and help the coating to stick better. 

3. Thin The Polyurethane

Thinned polyurethane can flow easier through the nozzle. If you don’t thin it, the thick flow can clog the nozzle. 

To thin water-based polyurethane, use water. To thin oil-based polyurethane, use mineral spirits or lacquer thinner. You must use a ratio of 4:1 (4 parts polyurethane to 1 part paint thinner). With this thinning ratio, the sealant will have a thin flow but still maintain its hard and moisture-resistant finish.

4. Prep The Paint Sprayer

To prep the sprayer, you must clean it. prime it,  and use the right nozzle tip. For polyurethane, use a nozzle tip between 1.0 and 1.5mm. To prime it, pour polyurethane into the paint cup and switch the multiport valve to the primer. Once the sealant starts flowing through the nozzle, the sprayer is fully prepared (and primed) and you can use it.

For spray-on polyurethane, prepping isn’t required. You just need to shake it for a few seconds and use it. 

5. Spray the Polyurethane

Test the sprayer to see if the finish is smooth and if it dries well. If the coating has a consistent flow and dries well, you can use it. 

To spray polyurethane, use a pressure of 28 PSI. Generally, clear coats must be applied with a pressure set between 26-29 PSI. At this pressure, the sealant can be well atomized to the surface. 

If you use a lower pressure than 25 PSI, the sealant won’t expel smoothly from the nozzle. Since polyurethane is thick, you must use more pressure to expel it smoothly on the surface. 

While spraying, cover the surface with overlapping coats, keep the nozzle 10-inches away from the surface to avoid splashes, and apply thin coats. 

You need 2-3 coats of polyurethane for proper coverage. You must allow it to dry for 3 hours before recoating. You also must sand between coats with 320-grit sandpaper. The final coat doesn’t need sanding. 

You must allow the finish to dry for 3 days before using it.

Is Spray Polyurethane Good?

Polyurethane spray paint is a great finish and works well on different surfaces, including wood. It offers moisture and scratch resistance features. In addition, exterior polyurethane offers weather and UV resistance to the surfaces.

This sealant is one of the strongest and best finishes in the painting world. The word “urethane” is a plastic-like material that dries hard. When it 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.

Spray vs Brush Polyurethane

Spraying polyurethane is better than brushing it because it is easier to apply and gives a better finish. Since it is easy to apply, it can be used by beginners. Brushing will reveal brush marks and strokes if applied by a beginner. 

Here are more reasons why spray-on polyurethane is better:

1. It offers better coverage over the surface.
2. You don’t need to prep it.
3. You can cover a surface faster.
4. Covers the surface evenly.
5. Doesn’t reveal brush marks. 
6. It is easier to apply
7. It offers a better finish quality. 

Final Words

You can spray polyurethane, but you must thin it and use the right nozzle (1.0 – 1.5mm). You can also use spray-on polyurethane.