How to Clean Polyurethane Brush

How to Clean Polyurethane Brush Hairs Effectively

Ian Mutuli
Updated on
Ian Mutuli

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.
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No paint job is complete without the responsible post-clean-up processes. As such, cleaning your polyurethane brush is essential, especially if you don't intend to buy a new brush the next time you have a paint job. Therefore, maintaining a clean polyurethane brush helps you have a ready paint brush in your store in the days to come.

That said, understanding how to clean polyurethane brush bristles begins with acknowledging the different chemicals your brush has been exposed to. Ideally, cleaning polyurethane from brush hairs should be done as soon as you finish your paint job to avoid the hardening of paint on the bristles. Notably, when all those chemicals found in paint harden on your brush, they eventually ruin it.

In this context, we will focus on the process of cleaning a polyurethane brush both immediately and even with dried polyurethane on it. Bottom line, as you keep your knives sharp all the time, brush bristles deserve care after use. Nonetheless, let's know what we are dealing with by understanding the concept of polyurethane.

What is Polyurethane?

Polyurethane is a liquid coating applied on top of paint or a wood surface to maintain freshness. Subsequently, this substance plays a vital role in maintaining and revamping wooden surfaces. When handling polyurethane, it is important to note that it's thick in consistency and is complex to handle. Therefore, polyurethane is more demanding than ordinary paint.

One of the aspects that make polyurethane demanding is the cleaning process. So, you need a good clean-up technique to ensure that polyurethane brush residues are disposed of safely. In light of the complexities involved in handling this substance, let's proceed to the details of a good clean-up.

Polyuthereane Types

In light of the complexities involved in handling polyurethane, it is also critical to understand the different types of polyurethane. As a result, there are two types of polyurethane: water-based and oil-based poly. For both types, polyurethane dries very fast, and when dry, it can't turn to liquid form even with exposure to chemicals or heat.

1. Water-Based Polyurethane

This type of polyurethane is easy to use compared to its traditional oil-based coating. To begin with, this type is low on toxicity and odor and is also easy to remove than the oil-based one. In addition, some users prefer the water-based option since it preserves the natural wood tone and color. However, this option isn't very durable and will require frequent repeats in maintaining wooden surfaces.

2. Oil-Based Polyurethane

On the other hand, the oil-based is more durable, just like oil-based paint, but this comes with the sacrifice of increased odor and toxicity. As such, oil-based polyurethane coating is cheaper than its water-based counterpart and adds color to your natural wooden surfaces. Some users don't prefer the oiled option since its odor can settle on household items like beds and even clothes.

It is worth noting that both types are toxic, and their disposal and exposure should be handled with care. Now, let's proceed to the process of how to clean polyurethane brush bristles for both types.

How to Clean Polyurethane Brush Bristles

There are two methods of cleaning polyurethane from a brush, depending on the type of polyurethane used. Follow through the processes below to obtain a clean brush for both cases.

Method 1: Cleaning Water-Based Polyurethane

This first method is less labor-intensive due to the easy handling of water-based poly. But, the first step should be rechecking your polyurethane container to confirm its oil or water-based. Consequently, you only need water to clean your brush in this context. Nonetheless, there is a process to follow for optimal outcomes and safety.

What you Need

  • Water
  • A container
  • Pair of gloves


Start with filling your container with water for cleaning your brush. Next, use your gloves to clean your brush in the container thoroughly to remove water-based polyurethane residues from your brush. Repeat this first process around four times, each time using clean water. Ideally, you will know when to stop when your water remains clean and clear.

Just to be sure you have gotten rid of all the water-based polyurethane, proceed to your sink area for thorough flushing with clean running water. This follow-up step will rid any remaining poly residues from your brush. However, while at the sink, proceed with caution to avoid paint splattering everywhere. Overall, ensure you wear your gloves at every step as you wring out your brush as much as possible.

In some instances, you might prefer to soak your polyurethane brush in water. You can leave it soaked for some time as part of getting rid of all the water-based polyurethane from the brush hairs. Nonetheless, you shouldn't soak for too long, considering that long exposure to liquid can distort the bristles.

Method 2: Cleaning Oil-Based Polyurethane

Tackling the oil-based polyurethane is more complex than method-1. Nonetheless, it is still DIY.

What You Need

  • Paint thinner/white spirit
  • Acetone
  • Water
  • Dish soap
  • Mask
  • Gloves
  • Container


As earlier highlighted, water isn't enough to clean oil-based polyurethane. The first step is to soak your brush in paint thinner but for a few hours, especially for fresh polyurethane. Without paint thinner, you won't be able to remove polyurethane from brush hairs since it is an oil solvent. After adequate soaking, massage your brush through its hairs to ensure that you leave all the oil-based polyurethane in the thinner.

After adequate washing and massaging in the thinner, apply some acetone on the brush to remove the thinner. Then, follow-up the acetone wash with a final wash using water and dish soap. Again, water and soap are used to get rid of the acetone. This final step might feel like too much, but it is necessary for longer service, even with good quality brushes.

In the final washing step, soap will also help soften the bristles to maintain their flexibility for future use. Eventually, wash polyurethane brush hairs with water to remove the soap residues. It is recommended that you do the water wash in a sink to remove polyurethane from a brush completely. Throughout this process, you should wear gloves and a dust mask while keeping your windows open.

What if the Polyurethane is Dried on a Brush?

A paint job can sometimes be very tedious, making you stash away your brush without cleaning. In such a case, your brush will have dried polyurethane on it, making it difficult to use the already highlighted cleaning methods. Fortunately, there is a solution for removing dried polyurethane from a brush. This process will essentially remove the dried polyurethane and soften the hardened bristles.

What You Need

This process might sound complex, but it requires readily available supplies. Most of what we will list will probably be available on hand or in your local hardware store. Here is the list:

  • Mineral spirits.
  • Paper towels
  • Brush comb
  • Plastic bag
  • Two glass or plastic containers

Some users prefer to remove dried paint using household cleaning supplies like a fabric softener for the softening process. However, this latter method might be ineffective for oil paint and polyurethane. Also, regarding mineral spirits, some might choose to use paint thinner or lacquer thinner solvents. However, these alternatives might damage a brush.


As you clean polyurethane under dry circumstances, this process might also take the form of softening a hard paint brush. Subsequently, the process of softening hardened polyurethane begins with putting some mineral spirits on a paper towel for removing polyurethane. After reducing the polyurethane load on your brush, you can soak it overnight in mineral spirits.

Even so, the process of soaking needs to be approached carefully. Ideally, the metal bracket (ferrule) and the handle shouldn't touch the solvent at all. Therefore, you will need to measure the amount of solvent you add to your soaking container. Next, put your brush into the container with the solvent as you swirl it around to allow for deeper penetration into the bristles as you agitate the mineral spirits.

After a good overnight soak, transfer dirty mineral spirits to a disposal container. You can then repeat the initial steps and ensure your swirl your brush in the solvent for maximum cleaning power. This time, only soak for a few hours.

After you notice your brush is clean and the bristles have softened, proceed to rinse it using hot water. Do the hot water soaking in a separate container since the mineral spirits and polyurethane are hazardous. After an adequate soak, you can use dish soap to remove any remaining solvent. At this step, you will apply a brush comb to remove any excess paint and remaining polyurethane as your work through the brush hairs.

Eventually, finish your cleaning by using paper towels to dry your brush. You should gently pat your brush bristles dry to avoid pulling the bristle too hard. When your brush is dry, you can use the plastic bag or wrap to protect the bristles. In the case of natural bristles, you can wrap your brush with old newspaper.

Here is a quick outline of this process of restoring those beautiful bristles.

  1. Apply some mineral spirits on a paper towel to remove polyurethane.
  2. Soak your brush overnight in a container with mineral spirits.
  3. Transfer the dirty mineral spirits to a separate container
  4. Repeat the process as you deem fit
  5. Brush off with hot water or soapy water mixture
  6. Rinse your paint brush
  7. Dry your brush with a paper towel

Drying Your Brush

Under softening process, we have featured drying as the last process. This technique also applies to the initial two clean methods to keep your brush from hardening. Drying ensures that your cleaning isn't in vain.

As highlighted in the softening process, you can use paper towels to pat your brush dry. You can also gently wipe the bristles. Whichever approach you use, ensure that the bristles no longer drip water and you do it gently dry them to avoid pulling them out.

Storing Your Brush

Understanding how to clean polyurethane brush hairs wouldn't be complete without proper storage techniques. Similar to other work tools, a clean brush should be stored properly. If neglected, your bristles might become stiff or fall off at the extreme.

Already, we have highlighted you can use plastic wrap to store your dry synthetic brush and an old newspaper to wrap your dry natural bristle brush. However, this is not adequate for brush preservation.

If you are storing for a short time, you can leave a few bristles in the paint, and when taking a long break, you can use aluminum foil. Please note, after cleaning polyurethane brush hairs, you should avoid using plastic wrap for a long period to avoid drying your brush. Plastic allows moisture to reach the brush, causing it to dry.

Where to Store Your Brush

To complete the cleaning process, you can store your brush in a cool and dry place. Such conditions will help you keep moisture out while still allowing air to flow. As such, you can store your brush in a cardboard and expect it to still have a smooth coat after years.

Tips to Guide you the Brush Cleaning Process

1. Distinguishing the Type of Brush

This distinction is mainly between natural brushes and synthetic brushes. The highlighted cleaning procedures apply to both synthetic and natural hair bristles. Besides that, natural hair bristles are more delicate than synthetic bristles. Consequently, vigorous scrubbing doesn't suit natural bristles, unlike a quality brush with synthetic bristles, which can be bent without risk of damage.

2. Caution Working with Solvents

Solvents used to remove oil-based paints can be toxic if not handled properly. So, even as you learn how to clean polyurethane brush bristles, you should know that paint thinner and mineral spirits are made using harsh chemicals similar to polyurethane paint and other oil-based paints.

Therefore, we recommend cleaning polyurethane brushes or dried paint in areas with proper ventilation. Also, you should wear protective gear while cleaning brushes with solvents to avoid letting these chemicals onto your skin or into your eyes or mouth. If inhaled, ingested or absorbed on skin, you might encounter health problems that will require you to seek medical attention. Some of the safety gear to use include gloves, goggles, ventilated masks, and dust masks.

Taking this safety to another level, any oil paints or solvents like paint thinner or mineral spirits used to clean polyurethane shouldn't be washed off in the drain. Instead, you should collect used solvents in a separate container for careful disposal in a hazardous recycling plant.

Frequently Asked Question on the Cleaning Process for a Polyurethane Brush

1. Does vinegar remove polyurethane?

Yes, vinegar can remove polyurethane. Considering vinegar is alcohol-based, it can easily remove oil-based polyurethane. After using vinegar, ensure your rinse with water to maintain the integrity of the bristles.

Ian Mutuli

About the author

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.
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