Do you have problems with your water-based polyurethane being streaky or foggy when you brush it on? Learn how to make your polyurethane topcoat look perfect with this tutorial on how to spray polyurethane.
Check out my list of the Best HVLP Paint Sprayers here.
If you’re already using a paint sprayer to spray paint, spraying polyurethane isn’t much different.
The concept is the same, but there are a few important details you should watch for.
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How to Spray Polyurethane
What is the best water-based polyurethane for spraying?
To start out, this is my all-time favorite water-based polyurethane. I haven’t had problems with it turning yellow over white paint (unlike the Minwax polycrylic).
It’s available in gallons, quarts, and 1/2 pints.
You can also choose from Matte, Satin, Semi-Gloss or Gloss sheens! (My go to is Satin)
Even though I go through A LOT of polyurethane, I like to get it in the quart sizes instead of the gallon sizes.
Mostly because I find that there is room for more user error when it comes to the gallon sizes.
I’ll share more about that below.
How to Use Polyurethane
Before we go any further, let’s take a quick second to go over the basics. Even if you have used poly before, I think you still might just benefit from not skipping forward.
Mix it! – But seriously, don’t skip this step!
The very first thing you should do when you open a fresh can of polyurethane is mix it.
Yeah, that’s a pretty basic step. But are you doing it right?
This is where that user error comes in that I mentioned above.
See, I used to not mix my poly very well. And then one day, I ended up with foggy spots all over my fresh black painted buffet.
I had no idea what happened, so I researched it.
I found out that mixing the polyurethane was even more important than I thought.
The Flattening Agent Needs to be Mixed in Really Well
Inside your can of polyurethane is some flattening agent. They use it to change the sheen from gloss to matte (flat). As you can probably guess, there is more flattening agent in the matte sheen compared to the gloss sheen.
The flattening agent likes to fall to the bottom of the can, so the polyurethane on the top of the can has little to no flattening agent in it.
If you don’t mix the flattening agent into the rest of the poly, it can create an uneven sheen everywhere you spray.
Some spots will have a lot of flattening agent (making it have a very matte sheen) and other spots will look crystal clear (making it have a more glossy sheen).
This is why I like to buy the quart sizes of polyurethane.
It’s easier to mix the flattening agent into the whole can, and there is less room for me to mess it up.
Add some paint to your poly!
If you’re spraying poly over a dark color, try adding some of the paint color to your poly.
Just like usual, I don’t measure it out exactly.
But I would say that you really only to mix in a tablespoon or 2 per cup of poly.
When you add some of the paint color to the poly, it will help hide any streaks, fogginess, or uneven sheen that you might get.
Filter it! – Also super important!
Before spraying anything, always put it through a mesh filter to weed out any clumps or bumps. (Even if it’s a brand new can!)
Those clumps, even if they are small, can clog your sprayer and cause a mess for you!
I personally use these disposable filters.
Do you have to thin polyurethane for the paint sprayer?
Do you have to? No.
Is it a good idea to thin it? I think so!
Thinning polyurethane for spraying isn’t completely necessary (unless you want a super smooth finish.)
Thinned polyurethane will be able to lay down better, with less texture bumps. It will also dry to a buttery smooth finish.
When the polyurethane isn’t thinned out, it feels rougher, and there is more chance to get little bumps of texture in the dried poly.
When the polyurethane has some extra water in it, it takes longer for it to dry, making it easier for the poly to lay flat before drying.
How to thin water-based polyurethane for spraying
You can thin the polyurethane out the same way you would thin paint out. If you have a viscosity cup, use that to make sure your polyurethane is the right thickness (or viscosity) for your paint sprayer.
Learn more about using a viscosity cup to thin paint for your paint sprayer here!
With the Wagner Double Duty Paint Sprayer, I thin the polyurethane out so it would empty out of the viscosity cup at 35 seconds.
With my professional Fuji paint sprayer, I don’t measure as much, but I like to fill up my 8 ounce mini container with about 3/4 polyurethane and then put water in the last 1/4 of the container.
So that translates into 3 parts poly to 1 part water, for any size container.
Test it! – Before you spray your furniture!
Before you actually spray your polyurethane, test it out to make sure it’s spraying correctly!
Trust me, it doesn’t always spray perfectly right from the get go.
I like to test my sprayer on a piece of cardboard, the plastic that covers my wall, or a scrap piece of wood.
Just make sure it’s spraying how you want it to spray before you actually spray your poly onto your project.
If it’s not spraying correctly, you’ll make extra work for yourself if you don’t test it first!
Let it Dry! – Between coats and for at least 24 hours after the last coat!
Most everyone recommends 3 coats for the best durability.
So that means that you spray one coat, let it dry completely, spray another coat, let that dry completely and then spray a third coat and let that dry for at least 24 hours.
What does it mean to let it dry completely?
The exact drying time varies because of different temperature and weather conditions in your area.
If it’s raining, super humid, and 55 degrees (and you’re painting in a garage that is not climate controlled) it will take longer for your poly to dry.
But if it’s a sunny, dry, 90 degree day, your poly will dry very fast.
If you spray the poly super super thick ( I don’t recommend that!) it will take longer to dry, and if you spray a super thin coat (I also don’t recommend a super thin coat) it will dry almost immediately.
Varathane recommends waiting 2 hours between coats.
I personally can usually recoat in about 1 hour.
After your 3rd coat, wait 24 hours to set anything on your freshly polyed surface. Ask me how I know. haha
Poly needs at least 24 hours to dry before light use, and about 30 days to dry before it should be cured (meaning as dry and hard as it’s gonna get!)
Best Paint Sprayer for Polyurethane
I don’t know that there is exactly the perfect paint sprayer for polyurethane.
Both paint sprayers that I have had worked well with poly.
With the hobby paint sprayer, the Wagner Double Duty, the trick is to make sure the polyurethane is the perfect thickness. (about 30-35 seconds for the viscosity cup).
I used the Wagner Double Duty for 3 years before I upgraded to the Fuji Q4.
The Q4 is definitely an investment that isn’t for everyone. (Read my Fuji Q4 Paint Sprayer Review here.) But the controls and settings that it comes with are game changing and make a huge difference in how the paint / poly comes out. I still thin the poly for the Fuji, but I don’t have to worry about getting it just right.
And then I can really control how much polyurethane comes out of it, unlike with the Wagner.
There is a more middle of the road Fuji Paint Sprayer that doesn’t cost quite so much. It’s called the Fuji Semi Pro. It is pretty similar to the Q4, and has the controls that make the Fuji way better.
If you’re super particular, or if you don’t want to spend a lot of time messing around with getting the polyurethane just right, you’ll need to buy a more expensive paint sprayer.
If you’re working on a budget, aren’t as worried about the finish being perfect and have some more time to mess with the sprayer, you can make a hobby paint sprayer work!
UPDATE: I recently bought the Wagner FLEXiO 3000… and it sprays amazingly well. Check out this nightstand makeover to see how using the Wagner FLEXiO 3000 works.
Do I need to have a separate sprayer for polyurethane?
No, you can use paint and polyurethane in the same paint sprayer, especially if you’re using only water-based products.
Actually, I like to empty out my paint and leave just a little bit of the paint in the container, and then put the waterbased polyurethane in the sprayer. It tints the polyurethane a little bit and makes it look so much better when you spray it on top of dark colors.
If you’re using some oil-based, some water-based and some shellac-based products, you might want to get separate sprayers.
But I like to stick to only water-based products in my paint sprayer.
Can I spray oil-based polyurethane?
You can! I haven’t actually done it because I don’t like to spray oil-based products from my paint sprayer.
But that doesn’t mean that it can’t be done!
Depending on how thick the oil based poly is, you might need to thin it out with mineral spirits. You can thin it out using the same method as the water-based poly!
Just make sure to use the correct thinning agent (mineral spirits for oil-based products, and water for water-based products)
Use a Spray Can Version of Polyurethane
Another option is to use the spray can version of oil-based polyurethane.
Whenever I want to spray oil-based poly, I go for the spray paint version of the Minwax Fast Drying Polyurethane (linked below).
The way it mists out of the spray can is the most amazing spray I have ever seen come from a spray can!
UPDATED: I recently tried the Varathane oil based poly in a paint can and it was a mess (I tried two different cans too!). Both cans spit big fat drops of poly all over my project
So if you want to use a spray paint kind of oil based poly, I really recommend that you stay away from this Varathane oil based spray can, and instead, use this Minwax Fast Drying Oil Based Poly. You won’t regret it!
UPDATED AGAIN: I recently tried the Varathane water based poly in a spray can, and I don’t recommend it. But I tried the Minwax Polycrylic in a spray can and it created a beautiful finish!
Crazy huh? Because up at the top of this post, I told you that I recommend Varathane water-based poly instead of the Minwax water-based poly.
I guess it just goes to show us that some brands are good for some things, while other brands are good for other things!
The dried polyurethane feels rough, how do I get it to feel smooth?
We talked about thinning your polyurethane to make it feel more smooth, but there is another step you can take to make sure it feels more smooth.
Don’t spray your polyurethane in full sun, or in the heat.
You don’t want it to be under 50 degrees though.
You want to find a nice place where the polyurethane can dry slowly.
If the polyurethane dries too fast, it can result in those textured bumps and it can make the poly feel rough.
Sand between coats!
Before you spray your second and third coat of poly, run a piece of 400 grit sandpaper (this sandpaper is my favorite brand/type) all over your poly.
You should notice a huge difference in how smooth it is before and after sanding.
Then wipe away all the white powder left from the poly. (I like to vacuum up the dust and then use a tack cloth to wipe any excess away)
Make sure you have enough ventilation when spraying.
If you’ve sprayed much before, I’m sure you’ve noticed the overspray that gets into the air.
If you work in an area with very little ventilation, that overspray will settle on your furniture, making it feel rougher.
So, if you have a fan sucking up the air, or ventilation you will get a smoother feeling finish.
I hope that helps!
Here is a video that may help you to spray polyurethane better!
Learn more about painting furniture with a paint sprayer:
- How to Prevent Overspray
- How to Paint with the Wagner Double Duty Paint Sprayer
- Can you Spray Milk Paint?
- How to Spray Paint a Dresser with Chalk Paint
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