How to Clean a Polyurethane Brush? (Water & Oil-Based)

You must clean paintbrushes after painting to keep them in good condition. So, how to clean a polyurethane brush?

To clean a polyurethane brush, squeeze as much sealant as you can off it. Then you need to soak it in a bucket of solvent or paint thinner for 10 minutes.

You may need to dilute the concentration of the paint thinner depending on the potency of the liquid. After 10 minutes, take the brush out and wipe it with a clean rag.

Stuck polyurethane residue can be removed using a soft toothbrush. When the brush is clean, rinse it with warm water and store it.

Why Should You Clean it?

You must clean a brush to make it last longer. After applying polyurethane, its residue will stick on the paintbrush and if you don’t clean it fast enough, the residue will dry and harden over it. The solidification process of the polyurethane can cause the bristles on the brush to dry out.

1. Mixes With The Next Paint

If you don’t clean a paintbrush after using it to apply tinted polyurethane, you risk the sealant color dissolving and affecting the color of your next paint job.

2. To Save Polyurethane

Sometimes, the paintbrush takes more sealant than is needed from the paint can. After painting, you might still have leftover sealant on it that you can squeeze back into the can while cleaning it. This helps to prevent wastage.

3. For Easy Paint Application Next Time

Cleaning it after applying the paint makes your next painting task easier. With the paintbrush clean, you can easily apply paint with it next time. Cleaning also saves the time you would have spent on your next task.

Product To Clean It

What Can You Use To Clean Polyurethane Brushes

You can use solvents or paint thinners to clean it. However, the cleaning agent you will use depends on the type of sealant (water or oil-based). 

To clean a water-based polyurethane brush, use soapy water. To remove oil-based polyurethane use mineral spirits.

Mineral Spirits

You can use mineral spirit to remove oil-based polyurethane from a brush. Mineral spirits is strong enough to dissolve oils and particles of the sealant. It can also remove the water-based type, but it’s too strong and there are better alternatives for that. 

However, don’t soak it in mineral spirits for too long as it can damage it. 

Water

You can use soapy water to remove water-based sealant from a brush. The water-based polyurethane uses water as its solvent, so if you add more water to it, the sealant will get removed. However, you can’t use water to remove the oil-based type. 

Acetone

You can use acetone to clean it. Acetone is a natural paint thinner that is effective for cleaning both water-based and oil-based polyurethane.

However, use acetone to only clean or wipe it. Never soak a paintbrush in acetone because it can soften its plastic parts and will dissolve and lose shape if left in the acetone for too long.

Alcohol

Alcohol is an effective paint-removing compound used to remove water-based sealants. You can also soak the paintbrush in a bucket of rubbing alcohol to dissolve the sealant residue since it doesn’t corrode or damage the plastic.

Paint Thinner

You can use paint thinners to clean it, but don’t soak a paintbrush in paint thinner for more than 30 seconds. 

Paint thinners are produced from a combination of several chemicals, including acetone, xylene, mineral spirits, and turpentine. These chemicals are strong enough to cause corrosion.

Paintbrushes should always be rinsed in clean water after using paint thinner to clean them.

You can also clean it:

  • Turpentine (for oil-based)
  • Denatured Alcohol (for water-based)
  • Warm Soapy Water (for water-based)
  • Lacquer Thinner (for oil-based. Don’t soak the brush in lacquer thinner)
  • White Spirits (For water-based).

How To Clean a Polyurethane Brush?

Cleaning polyurethane off brushes is an easy task. Here are the tools you need:

  • An empty bucket
  • Water
  • Paint thinner
  • A pair of gloves
  • Dish soap
  • A soft toothbrush

1. Squeeze The Excess

Squeeze The Excess Polyurethane

Start by squeezing as much polyurethane from the brush as you can. To do this, wear gloves and manually squeeze it out.  You can squeeze the excess back into the container and use it later. 

You must be careful while squeezing as you can ruin its shape of it. 

2. Fill A Bucket Halfway With Paint Thinner

Fill A Bucket Halfway With Paint Thinner

For water-based polyurethane, use water as a paint thinner. For oil-based polyurethane, use mineral spirits. You need to pour enough paint thinner into the bucket to remove it.

Since mineral spirits is expensive, you can dilute it with water. This way, you can fill half of a bucket without wasting too much of it. When mixing mineral spirits with water, use a ratio of 2:1 (2 parts mineral spirits 1 part water). If you use more water than mineral spirits, the mixture won’t be strong enough.

3. Soak and Swirl The Brush 

Soak and Swirl The Brush In The Bucket

Soak the brush in the bucket filled with paint thinner for 10 minutes. After, swirl it inside the bucket to shake off the loose sealant.

4. Use a Soft Toothbrush

Remove Stuck Paint With a Soft Toothbrush

After 10 minutes of soaking it in the paint thinner, take it out and inspect the brush. Chances are you’ll notice stuck polyurethane residue between the bristles. The excess can be removed using a soft toothbrush. Glide the toothbrush through the brush to remove struck poly. 

For tough or stubborn water-based residue, add dish soap to water and use soapy water to remove it. For oil-based residue, add a few drops of mineral spirit directly to it and stoke it out with a toothbrush.

5. Rinse With Clean Water

Rinse The Brush In Clean Water

Fill a bucket with water, and soak the paintbrush into the bucket. This helps remove leftovers and paint thinner from the brush. This step is important, especially after using a strong paint thinner.

6. Leave It To Dry

Leave The Brush To Dry

Let the brush dry, then inspect it before storing it properly. If there’s no sealant left, you can store it..

Cleaning Between Coats

You don’t have to clean your brush between coats. Instead, you can seal it in a plastic bag and place the bag in the fridge for a few hours until it’s time to re-coat.

The brush must have some polyurethane left before being sealed off in the plastic bag. This will keep it fresh and ready for application even after hours of waiting for the existing coat to dry.

But, if the wait time is over 48 hours, you must clean it between coats. On average, you must wait at least 2 hours before you re-coat it. Oil-based polyurethane can take up to 12 hours to dry before re-coating it.

Related Read: Can You Thin Polyurethane Paint?

Final Words

Overall, cleaning your polyurethane brush after painting helps to keep it in good condition. But you don’t have to clean the brush between coats. Instead, seal it in a plastic bag and refrigerate it for a few hours. This will keep it fresh and ready to use for the next coat.

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