Step-by-Step Guide to Clean a Polyurethane Brush

By MWB-Team •  Updated: 06/10/23 • 

Finishing brushes are an investment for a woodworker, so you should take care of them. After using a brush to apply any finish, proper cleaning and maintenance should be done to remove the finish residue and maintain the brush’s profile. In this article, we’ll guide you on how to clean a brush after applying polyurethane.

Water-Based vs. Oil-Based Polyurethane

Both water-based and oil-based polyurethane offer good protection when applied to wood surfaces. The biggest difference between these two is their drying times and the final appearance. Water-based polyurethane dries faster and cures to a crystal-clear coat. Oil-based polyurethane takes more time to dry and cures into a slightly yellowish hue, which darkens with age. Read more about water-based vs. oil-based poly.

When applying water-based or oil-based polyurethane, you can use a roller, spray gun, or a brush, which is the most used applicator of your choice. Brushing poly is cheaper and easy, even for amateur wood finishers. You should use a synthetic brush for water-based polyurethane since a natural bristle brush will soften and can get uncontrollable in water. You can use either a natural or synthetic bristle brush for oil-based poly.

With that said, once you’ve used a brush on either water-based or oil-based poly, there will be some cleaning afterward. Below are the steps to clean your brush and store it properly.

How to Clean Polyurethane Brushes

If you use your polyurethane brush regularly, you can wrap it properly with plastic or hang it inside the thinner of the finish until your next use. However, if your brush is not used regularly, it should be cleaned properly and stored.

Cleaning a finishing brush will include the same last steps. However, the initial steps will be specific to the finish you are cleaning off the brush. For polyurethane, the two types are water- and oil-based polyurethane.

How to Clean a Water-Based Polyurethane Brush

How to Clean an Oil-Based Polyurethane Brush

Keeping your brush clean after use will take only 5 to 10 minutes. After using your brush, make it a routine to clean it. This will make you feel better the next time when using the brush; it is clean, soft, and springy rather than stiff and difficult to work with. Keeping the brush clean will also keep it running longer for years.

Reviving a Harden Polyurethane Brush

If you forget to clean a brush after applying polyurethane, it hardens as the polyurethane finish hardens. This makes the brush unusable because of its rock-hard shape. However, you can easily bring it back to life if it is an expensive brush.

First, get a finishing stripper that works with polyurethane, such as an NMP-based stripper like Citristrip. It is gentler on the brush bristles, but handle it carefully and use protection while using the stripper.

Citristrip Stripping Gel
$21.48 ($0.67 / Fl Oz)

The Citristrip is a stripping gel that can easily strip different finishes from wood from polyurethane, varnish, lacquer, shellac, latex, and oil-based paints. Apply the stripper and let it sit for a few hours for the best results. It is easy to use and works well when stripping different finishes.

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Soak the brush in the stripper for several hours, then start working the stripper into the bristles of the brush using gloves. You can also hold the brush on a solid surface and use a wire brush to remove the softened polyurethane.

Once you’ve removed all the polyurethane, clean the brush in warm water mixed with detergent. Comb the bristles to remove any last poly finish that may be stuck, and rinse it again in warm water. Wrap the brush using a paper towel and store it properly.

MWB-Team

Hello there! This is the Make Wood Better Team. Here, we share informative how-tos and guides focused on making wood better. Whether it's finishing wood, maintenance, or restoration, there's something on this website for you to learn and improve your skills.