How to Clean Polyurethane Brush Like a Pro

Learn how to clean polyurethane off brush.
How to Clean Polyurethane Brush Image

With the amount of money spent on applying polyurethane, it is helpful to know that you can reuse some tools. From the polyurethane itself to the rags, sandpaper, mineral spirits, and tack cloths, nearly everything else can only be used once, but not the brush.

However, if you don’t know how to clean polyurethane brush, that’s money down the drain.

In this article, I’ll show you how to clean brushes used for oil-based polyurethane application and water-based polyurethane. You’ll also learn how to choose the right brush and why it is important to take good care of your tools.

Here’s a quick overall version of how to clean polyurethane from brushes.

How to Clean Polyurethane Brush

  • Use clean water and soap for cleaning water-based polyurethane brushes.
  • For oil-based polyurethane brushes, clean with mineral spirit. Then scrub the polyurethane brush under running water (and soap) with a nylon brush.
  • Let the brushes dry and store them in cupboard packages.

What Type of Brush do you Need to Apply Polyurethane?

How to clean polyurethane Brush image

There are different types of brushes that can be used to apply polyurethane. When you’re applying oil-based polyurethane, you should use a brush with natural bristles. They are made with animal hair, so they are better equipped at absorbing and spreading oil finishes.

The downside of natural bristles is that they are pretty expensive, so it is important to take good care of them.

Synthetic bristles, particularly synthetic nylon bristles, are best for the application of water-based finishes. This type of brush does not pick up a lot of moisture, making it great for water-based polyurethane.

Synthetic bristles are arguably more versatile than natural bristles, give a more even coat, and are cheaper.

Now, it’s time to look into cleaning each polyurethane brush.

How to Clean Water-Based Polyurethane from a Brush

The process for cleaning a brush used for water-based polyurethane is so simple; it is often overlooked. All it takes is a few minutes, and your synthetic brush will be ready for use.

Tools You’ll Need and Steps to Clean Polyurethane off Brush.

  • A pair of gloves (optional)
  • 2 or 3 cups
  • Running water
  • Dish soap

Step 1: Fill Three Cups with Clean Water

Get three cups that are large enough for you to submerge the brush up until the ferrule – the metal part that holds the bristles.

Step 2: Put the Brush in the Cup of Water

Insert the brush in the first cup and bend it back and forth so that the water gets in-between the bristles and up to the ferrule. Do this a few times until the water changes color.

Step 3: Move on to the Next Cup of Clean Water

When one cup of water becomes dirty, move on to the next one and repeat the process until the water in the final cup is clear.

Step 4: Wash the Brush with Soap

Head over to the sink and rinse the brush with running water. Then pour some dish soap on it and give it a good scrub with your hands.

Wash it for about two or three times or until the bristles feel squeaky clean.

Step 5: Hang it to Dry

You can either hang the brush over the sink or hang it in your workshop. The brush will be completely dry by the next day and ready for reuse.

How to Clean Oil-Based Polyurethane from a Brush

Brushes used to apply oil-based polyurethane are significantly more dirty than synthetic brushes. However, you can still clean the polyurethane brush in a few minutes. Always clean your brushes when they are still damp.

Tools You’ll Need

  • A pair of gloves (optional)
  • 3 cups
  • Turpentine, paint thinner or mineral spirits (depending on the instructions on the can)
  • Running water
  • Dish soap
  • Nylon scrub brush

How to Clean Polyurethane Brush with Mineral Spirits

Step 1: Pour Mineral Spirits

Pour mineral spirits into three or four cups. There should be enough spirit in each cup for you to submerge the brush up until the ferrule. 

Step 2: Dip the Brush in the Mineral Spirits

Image courtesy of The Spruce

Submerge the brush into the first cup of mineral spirits and hold it down so that all of the bristles get covered. Next, stir the brush about in the cup, bending over from side to side so that the mineral spirit gets in-between the bristles.

Step 3: Move on to the Next Cup

Once the color of the mineral spirits changes (turns dark brown), move on to the next cup. Repeat the process in all three cups, making sure you wait patiently for the color to change in each one.

Keep going until the color no longer changes despite slushing the brush around in the cleaning agent. You might need to go through this process four or five times to get it ready for the next step, so feel free to get more cups of mineral spirit if needed.

Step 4: Scrub the Brush under Running Water

Even after the mineral spirits remove all the polyurethane from the brush, you still need to wash it thoroughly.

First, rinse the brush under running water, then apply household dish soap and give it a thorough scrubbing. Run your fingers in-between the bristles, press it against your palm, and just scrub it however you can with your hands.

The first pass with dish soap won’t lather, as the mineral spirits are still in the brush. You need to get all of this out. Rinse and repeat until you get a clear, generous lather from the brush with the same quantity of soap.

Step 5: Scrub it with a Nylon Brush

Put the brush at the bottom of the sink, apply some soap on it, and give it a gentle scrub with a nylon brush. The nylon brush will be able to clean between the bristles better than your hand can with significantly less pressure.

You may need to repeat this step one or two more times before the brush is completely oil-free and squeaky clean.

Step 6: Dry the Brush

You can either hang the brush over the sink or hang it in your workshop. The brush will be completely dry by the next day and ready for reuse.

Why do You Need to Clean a Polyurethane Brush?

Have the Polyurethane Brush Handy

When you are making a career out of woodworking, and even if you’re not, you will come to appreciate the importance of always being ready. While you would probably get advanced notice for some jobs, some pleasant surprises might spring up, and you should be ready to act.

Having your brush ready can save you from having to go out to buy one at a moment’s notice or trying to wash a hardened brush you ignored since your last job.

Maintain the Quality of Your Work

When you don’t wash your brush early, it becomes calcified in the polyurethane and much harder to wash. You can then end up damaging the bristles as you wash them.

So, the next time you use the brush, the application won’t be as even as before, and you will need to put in more effort to get a smooth finish.

You may be thinking, “It is water-based polyurethane. It’s thin. It won’t have an effect later on. The brush won’t need cleaning.” You will be wrong. As long as it wasn’t clean water that the brush was used for, it’ll have adverse effects on the quality.

It Shows Professionalism

When people know you as the DIY pro, they’d always expect you to have some tools handy. So if someone comes to your house to ask for a brush, it’s good to have one ready. Saying, “Oh, give me a second to clean up,” is not a good look.

An extension of this point is the need to always have a clean and organized workshop.

Prolongs the Life of Your Polyurethane Brush

How long can a brush last? If it’s a quality brush that you look after keenly, it can last for up to a decade or more before it starts letting you down.

Both natural and synthetic brushes can last for ages if you clean them immediately after jobs and keep them dry when not in use.

Cleaning Polyurethane Brush is Good for Your Health

As you probably know by now, polyurethane contains VOCs, and you probably also know that they can be toxic with long-term exposure. That’s a risk you shouldn’t take. Keep your tools clean and all your chemicals covered when not in use.

How to Clean Brush After Polyurethane FAQs

Can you Reuse a Polyurethane Brush?

Yes, you can reuse a polyurethane brush. As long as the bristles are intact, you can keep using the brush you use for either water-based or oil-based polyurethane applications. Preserve the integrity of your brushes by cleaning them immediately after jobs, following the steps outlined in this post.

Can I use the Same Polyurethane Brush for Water-Based and Oil-Based?

While you can use the same brush to apply both water-based polyurethane over oil-based, you will not get the same results with both. Natural brushes are better suited for oil-based applications, while synthetic nylon brushes are much better for water-based polyurethane.

However, if you don’t have an option, you can use the same brush as long as you thoroughly cleaned it after your last job.

How do you Clean Polyurethane From a Brush Without Paint Thinner?

If you used the brush for water-based polyurethane, you don’t need to clean it with paint thinner. Instead, all you’ll need is clean water and regular dish soap.

For oil-based polyurethane brush, dip it in mineral spirits or turpentine. You will then need to give it a good scrub with a nylon brush and regular dish soap.

Save Your Money

As you can see, learning how to clean a polyurethane brush will save you a lot of money in the long run. Instead of buying a new brush for each job, you can use the same one for years.

Besides that, there are other advantages of keeping your tools clean, such as protecting your health and your image as a professional.

How have you been cleaning your brushes after jobs? Leave a comment below. Who knows, we might learn something.

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