How To Remove Dried Polyurethane From A Paint Brush? (7-Step Guide)

What Do You Need To Know About Cleaning Dried Polyurethane From A Paint Brush?

Brush cleaning is an essential part of maintaining your paintbrushes long term.

Why? Because those brush bristles deserve some love! They do a lot of hard work and they interact with all those chemicals in the paint that you're using.

So whether they're natural hair bristles or synthetic, they still need to be maintained in order to keep performing year after year, project after project.

This all starts with having a good clean up technique that will help you clean brushes with care and (ideally) immediately so that paint doesn't have a chance to turn into hard paint that will ruin your brush in the long run.

However, if you do have a brush with a bunch of hard polyurethane stuck on it, don't worry! 

You can still restore those bristles with a few simple techniques. 

But we'll get to that in a minute, first let's talk about brush care!

Being Gentle With Brushes

There's one important thing to call out here before we jump into the actual steps necessary to soften your brush bristles, and that is how you attack those brush bristles!

High quality brushes deserve quality care and attention. And that's not just because you should treat your nice things well...nicely...but it's also because being gentle with those bristles will actually contribute to the paintbrushes longevity.

This is for one simple reason: glue.

Glue? Yes, you read that right. Those bristles are glued into the part of the paintbrush called the ferrule, which is the metal bracket just below the bristles that hold the bristles in place.

If you go in and attack those hardened bristles with some vigorous scrubbing, you run the risk of pulling some of those bristles out of place.

While losing a few bristles during a brush cleaning isn't the end of the world, it can certainly add up over time.

And when you're working with good brushes, you want to maintain their quality - and their bristles - for as long as possible.

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Cleaning Synthetic Brushes vs. Natural Brushes

While many of these techniques will apply to either synthetic or natural hair bristles, there are a few key things you need to know about each type before you proceed.

The first thing to note is that natural hair bristles need to be treated even more gently than synthetic bristles.

That's because they are much more prone to permanent breakage. Because...well...they're natural!

Real hair breaks. Whereas synthetic bristles can often be bent back into place once they start to get wonky, natural hair will bend and stay bent forever.

So whatever level of care you thought you should use based on the previous section, double it for natural bristles!

Don't be discouraged though, no matter what type of bristles you're working with we'll give you our best DIY tips for getting that dried paint off so you can get back to painting.

Safety When Working With Solvents

Before we dive into the actual "how-to" of cleaning the polyurethane off your brush, it's important to note that you'll need to be working with harsh chemicals like paint thinner when cleaning brushes.

These chemicals are highly caustic and can cause damage to your health if not handled properly, just like polyurethane paint or shellac or any other oil-based paints or solutions.

It's important that you only work in well-ventilated areas while working with these chemicals and that you use gloves, goggles, and ventilated masks when working in direct contact with these things.

They can cause serious health problems when inhaled, absorbed through skin, or ingested, so please handle with care.

Supplies You’ll Need To Clean Polyurethane Off Your Paint Brush

When you're going to clean any brush, it's important to remember that there are some key supplies you'll need to get that dried paint off. 

However, it's likely that you have quite a few of them on hand already, and you'll only need the other ones if that dried paint just won't come off with your basic cleaning supplies.

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

Some people recommend cleaning methods that involve fabric softener or other household cleaning supplies to soften your brush. 

However, when working with oil paint like polyurethane, you can't simply rely on soap to remove the paint. You also can't just wash the runoff down the drain as these chemicals are toxic and aren't meant to enter the sewer system.

So for this cleaning method, I'm recommending you use mineral spirits, which are the best way to remove oil-based paints.

Mineral spirits are pretty easy to find at your local hardware store or Lowes, but you can find them on Amazon as well.

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How To Soften A Hard Paint Brush (10-Step Guide)

1. Use a paper towel to remove some of the polyurethane
2. Put mineral spirits into container 1
3. Place brush into container 1
4. Transfer dirty mineral spirits
5. Repeat the process as needed
6. Rinse brush with hot water
7. Use a paper towel to dry

Step 1 - Use a paper towel to remove some of the polyurethane

First things first, take some of the mineral spirits you'll be using and saturate a small section of a paper towel. 

Note: You could use paint thinner or even lacquer thinner for this cleaning process if that's all you have on hand, however sometimes they can strip the brush and damage it, so I'd recommend sticking with mineral spirits when possible.

You're going to use this to try and saturate some of the brush bristles and remove some of the polyurethane before soaking.

This is just to kickstart the process and ultimately lower the amount of polyurethane that the mineral spirits need to remove overnight.

This will leave your brush cleaner after just one soak and create less work for you in the long run.

Just make sure you're using gloves during this process so you don't get any mineral spirits on your hands, and ensure that the area you're working in is well ventilated.

Step 2 - Put mineral spirits into container 1

Now, take some of those mineral spirits and fill up your first container to a level that will allow you to place the bristles in the container and have them saturated.

You want to measure this to make sure you're only soaking the part of the brush bristles that have the polyurethane on them. Ideally, you want to make sure the ferrule (metal part of the brush) isn't touching the mineral spirits at all.

Step 3 - Place brush into container 1

Next, it's time to place the brush into the container you've filled with mineral spirits.

This part is pretty simple, just make sure to swirl the brush around for a bit to agitate the solvent and allow it to penetrate the bristles for maximum cleaning power.

Then, you can simply leave the brush in the container for several hours or overnight.

Depending on how much the polyurethane has dried, you might need to let it sit a bit longer. But generally, an all-night soak will do the trick.

Step 4 - Transfer dirty mineral spirits

Now that your brush has gotten a good soak, take the container with the dirty mineral spirits and transfer it to a container for disposal.

Because mineral spirits, paint thinner, and oil paints are all caustic and hazardous materials, you'll need to hold on to this and dispose of it at a hazardous recycling plant near you.

These things cannot simply be thrown away and need to be handled with care. 

Step 5 - Repeat process as needed

Now before you go and soak it again, simply place the same amount of mineral spirits into container 2 and swirl the brush around again.

You'll probably see some promising results this time just from agitating the solvent and you likely won't need to let it soak again.

However, if you're just not seeing the results you want, you can allow the brush to soak for a few hours again and repeat the process.

Step 6 - Rinse the brush with hot water

Once you've removed the majority of the polyurethane paint from your paintbrush, you can go ahead and soak the brush with some hot water.

(Ideally, you'll want to do this in a bucket or a larger container because mineral spirits and polyurethane are NOT supposed to go down the drain.)

You can feel free to use some dish soap to create a soapy water mixture here as well if you feel like you need the extra help.

You can also use a brush comb at this point to work through the bristles and remove any excess paint that may be lingering.

Step 7 - Use paper towels to dry

Now that you've removed the remaining polyurethane from the brush, use some paper towels to pat the brush bristles dry.

Make sure not to pull too hard as this can loosen the bristles and lead to a shorter life span for your brush.

Then, when you're ready to store your brush for its next use I'd recommend wrapping it in plastic wrap to protect it if it's a synthetic brush, and wrapping it in some old newspaper if it's a natural bristle brush.

This will protect the bristles from bending or breaking during storage so they're perfectly straight and clean next time you need to use them!

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Final Thoughts On Softening A Hard Paint Brush

So now that you know the process of getting rid of that hardened polyurethane you can feel much more confident in restoring your brushes going forward.

Hopefully, implementing these painting tips and making sure you're cleaning your brushes as soon as possible after you finish a DIY project will keep your paintbrushes in great condition for years to come.

If anything, it'll prevent you from having to buy a new brush every time you find one has hardened to this degree.

Say goodbye to those sad, hard paintbrushes and hello to some new, shiny, happy brushes!