How to Clean Polyurethane Brush

After painting your wall, furniture, or dinner table, you’ll come to realize that you have polyurethane all over your brush, and leaving it like that will make things even worse. So to avoid throwing them away and having to spend on new brushes, let us share with you how you can easily clean them at home.

Table of Contents

What is Polyurethane?

Polyurethane coating is a liquid layer that is used in varnish, sealants, frames, bookcases and bedding. It dries fast and will not go back to its original liquid form even if you heat it up or use chemicals.

Types of Polyurethane

Water Based Polyurethane

Water based poly is a low-odor and low-toxicity type of Polyurethane that is easy to remove compared to the oil-based type. It also doesn’t have the ability to add color to the wood, so it will preserve it’s natural hue.

Water-based polyurethane has gained popularity over the years and although it is less toxic than oil-based polyurethane, it should still be used with caution.

Oil Based Polyurethane

Oil based poly is slightly more durable and much cheaper than the water-based type.

If you prefer oil-based polyurethane, you need to keep your windows open and keep the fans running for a few days for ventilation because the odor can settle into clothing, beds and curtains.

Type of Brush for Polyurethane

Natural Bristles

This type of paint brush is best used for oil-based polyurethane as they are made with animal hair and are better at absorbing and spreading oil. The downside is that a natural bristle brush is expensive, thus it is important that you take care of them.

Synthetic Bristles

This paint brush is best for water-based finishes as it does not pick up a lot of moisture, which makes it good for use with water-based polyurethane.

A synthetic bristle brush is also more versatile, can give an even coat and are cheaper than natural bristles.

How to Clean Polyurethane Brush For Water-Based Polyurethane Brush

What you will need:

  • 2 or 3 cups
  • Running Water
  • Dish Soap
  • Gloves (optional) 

Step 1: Clean Water

Fill in three cups with clean water. The cups should be enough to submerge the paint brush until its ferrule or the metal area that holds the bristles in.

Step 2: Dip the Brush

Put the brush into the first cup and bend the bristles back and forth to get the water in between the bristles and up to the ferrule. Repeat a few times until the water changes in color.

Step 3: Next Cups

When the first cup of water is dirty, move on to the second cup and repeat the process until the water in the third cup is clearer.

Step 4: Wash with Soap

Rinse the paint brush with running water and pour some dish soap on it, then give it a good scrub using your hands. Wash for about two to three times until the bristles feel clean.

Step 5: Dry

Hang the brush over the sink or in your workshop and let it completely dry before using.

For Oil Based Polyurethane Brush Using Mineral Spirits

What you will need:

  • 3 cups
  • Mineral spirits (check for instructions on the can)
  • Running water
  • Dish Soap
  • Nylon scrub brush
  • Gloves (optional)

Step 1: Mineral Spirits

It is important to clean your brushes while they are still damp.

Pour enough mineral spirits into three cups to be able to submerge the brush up until its ferrule.

Step 2: Dip the Brush

Dip the brush into the first cup of mineral spirits. Hold it down to get the bristles fully covered.

Stir the brush in the cup and bend the bristles over from side to side to get the mineral spirits between the bristles.

Step 3: Next Cups

Once the color of the mineral spirits turns dark brown, move on to the next cup and repeat the process in all three cups. Make sure to wait patiently until the color changes in each cup.

Keep going until the color no longer changes. Go through the process a few more times if needed before proceeding to the next step, so feel free to use more cups of mineral spirits.

Step 4: Scrub

Wash the brush thoroughly even after you have removed the polyurethane from the brush.

Rinse the brush under running water,  pour dish soap onto it and then scrub thoroughly. You can press it against your palm, run your fingers through the bristles or just scrub it however you can with the use of your hands.

At first try, you may notice no lather when washing the brush with the dish soap, this is because the mineral spirits are still in. So to get all of this out, you need to rinse and repeat until you get a generous and clear lather with the same amount of soap.

Step 5: Nylon Brush

Put the brush on the sink and apply some soap on it, give it a gentle scrub using a nylon brush or a brush cleaner, so you can clean between the bristles. 

Repeat this step up to two times to make the brush oil-free and squeaky clean.

Step 6: Dry

Hand the brush over your sink or in your workshop and let it completely dry before using.

Using Thinner

What you will need:

  • 3 cups
  • Paint Thinner
  • Running water
  • Dish Soap
  • Nylon scrub brush
  • Gloves 
  • Dust Mask
  • Microfiber brush

Step 1: Dip the Brush

Add a small amount of paint thinner or lacquer thinner to a cup and do not fill it to the top. Dip the brush into the cup and leave it in for about 20 minutes.

Step 2: Bend

Bend the bristles from side to side and bend it up until the ferrule or metal part. Otherwise, the brush will harden up. Avoid jamming it straight down.

Step 3: Wash

Wring out the brush as best as you can and repeat the process until the thinner is clear.

Wear your gloves and put the brush in the sink, pour some dish soap and work into the bristles. Rinse with running water and rub it against your hand and make sure it lathers up, as this is an indicator that the brush is clean.

Now rinse it again to remove the soap and bubbles out of the bristles.

Step 4: Dry

Get your microfiber brush or foam brush then clean and wipe the bristles until the brush no longer drips. You can also use a paper towel to dry the brush.

Tips for Cleaning and Storage

  • Do not let your brush dry up because it will be unable to put on a smooth coat of polyurethane finish, thus you will need to buy a new one.
  • If you want to go on a break from painting, you should leave ⅓ of the bristles in the bucket of oil paint or water based paint to prevent it from hardening.
  • For an extended break, you can wrap your brush with aluminum foil.
  • Clean the brush right after use to avoid drying out and remove every stain to make sure that it can still provide good brush strokes.

Benefits of Cleaning a Polyurethane Brush

Quality of Work

Clean your brush right after use because if you leave them with dried polyurethane for a long time, you can end up with damaged bristles which will negatively affect the brush marks and the quality of work the next time you use them.

Have a Brush Ready

You will come to appreciate the importance of always having tools ready, especially if you are into woodworking, but even if you are not, it is always wise to have clean paint brushes ready, as this will save you time and money from having to buy a new one.

Professionalism

If you are a DIY pro or you’ve built a career out of woodworking, clean brushes, and an organized workshop shows professionalism and might even get you more clients.

Longevity

Natural and synthetic brushes can last for many years if you clean them right after use.. You should also keep them dry and store them properly when not in use.

Cleaning Brushes is Good for the Health

Polyurethane contains VOCs that can be toxic with long-term exposure, and this is a risk you shouldn’t take. Thus it is best to keep your tools clean and the chemicals securely covered when not in use

Polyurethane Brush Frequently Asked Questions

Does acetone remove polyurethane?

Acetone is a fast-evaporating solvent that is exempted in the list of VOC and HAP products, which means it can be safe for use for removing nail polish, paint or finishes, they can also be used to make finishes work.

A large amount of acetone can remove mineral spirits from a polyurethane brush and dries it out quickly after lifting and shaking the brush.

Will rubbing alcohol damage polyurethane?

Some types of polyurethane are resistant to rubbing alcohol, if cleaned up immediately. 

However, most polyurethane topcoat or finish can be damaged by isopropyl alcohol, denatured alcohol or rubbing alcohol, thus it is important to repair the affected area by sanding it with fine grit paper and applying a thin film of oil or re-apply a thin polyurethane paint or coating to the wood finish.

How to Clean Oil Paint Brush Without Thinner?

If you do not have any paint stripper or thinner and you desperately want to remove dried paint or excess paint off your brush, you can use linseed oil, which is a friendly and safe option to remove oil based paint or water based paint.

Soak each side of the brush with linseed oil and soak the bristles thoroughly until the pigments stop coming off. Afterwards, wash it off with dish soap and water.

Conclusion

Knowing how to clean a polyurethane brush is an important way to keep and use them for a long period of time.

By cleaning your polyurethane brushes, you will maintain the bristles’ structural integrity, which means you will not risk damaging it and still allow paint to adhere to them. Clean your brushes by using the methods we’ve listed above to help them keep a smooth and even stroke.

It is also important to remember that you have to clean your brushes immediately after use and avoid leaving paint on them overnight as it will be harder for you to clean them the next day.