How to clean polyurethane brush without making a mess!

old brushes

Polyurethane is a synthetic polymer used in many hardware products, such as paint, adhesives, varnishes and foams.

Each of them has a different function, but it is most commonly used as a component of varnish, applied on finished paintings or wooden furniture.

Some carpenters or painters can use a diluted formula of polyurethane to spray it on the desired surface, but the most common way to apply it at home is using a brush.

However, this material is prone to get sticky after drying, so keeping the brush later can be messy. But you cannot simply throw away each brush every time you use it.

So, how to clean polyurethane brush?

What kind of polyurethane are you using?

The first thing you need to consider before you clean polyurethane brush is what material your polyurethane is based on.

Depending on the base component of paints or varnishes, you will need to use different solvents. There are two types of polyurethane: water-based and oil-based.


How to clean water-based polyurethane?

Water-based polyurethane is the easiest to clean, as it doesn’t need any chemical product to be removed.

For washing it off the brush you only need to rub it under running water with some liquid dish soap until the water comes out completely clean.

If you have used your brush with water-based polyurethane, we recommend not using it again with oil-based products, as they have different components and remains can affect the final result.

However, if you don’t have several brushes, you can reuse a single one after thorough cleaning.

How to clean polyurethane brush and a cat watching

How to clean polyurethane brush with an oil-base?

There are several chemical products you can use to clean polyurethane brush.

Some of them are conventionally used for these kinds of activity, and others aren’t.

What you should keep in mind for all the options is that the brush should still be damp.

If you try to wash your brush after the paint or varnish dried, the bristles will be hard and stuck together.

Even if you managed to remove the product, it’s highly probable there are still some remains that might affect the final result.

The different options are:

  • Paint-thinner
  • Mineral spirits
  • Turpentine
  • Gasoline

How to clean polyurethane off brush using paint-thinner?

clean polyurethane brush with thinner_

This is one of the most common solutions for cleaning any kind of product like paint or varnish, so it’s normal that it’s on this list.

The best way to clean your brush using this chemical, is getting a few jars where you can pour a bit of thinner.

You will need to use enough to submerge the brush bristles completely.

The idea of having several jars consists in creating a kind of cleaning circuit.

Put the brush in the first jar and rub it on the bottom, separating the bristles to allow the thinner to pass through them and take away the polyurethane.

Once the liquid is opaque, move on to the next jar and repeat the process, and so on, until there is no remaining paint in the jar.

If the solvent gets saturated with paint, it will no longer be able to remove it, so your brush won’t be ultimately clean.

If you are planning on using your brush tomorrow or soon, you can simply keep it inside the flask with thinner. This will prevent the paint form drying and you will not need to clean it every time.

Whether you want to make a thorough cleanse or leave for brush in a flask, here’s an extra tip you might find handy.

Chemical products can damage your brushes, especially if they are not the best quality.

But how to clean polyurethane preserving your brush’s bristles? Add a hint of clothes softener in the jar so that the bristles are not so affected and you can use your brush a lot longer.

clean polyurethane brush_

Use mineral spirits or turpentine

These are other two typical options you can use to clean paint or varnish off any surface. Did you know these two products are pretty much the same? But what is the difference?

Turpentine is a resin extracted from pine trees and later processed into a smelly liquid that is used a solvent for paints, a grease cleaner and sometimes as fuel. It is also called white spirit.

Mineral spirits are made out of petrol instead of having vegetal origin like turpentine, but the final result is pretty similar.

Turpentine is a stronger diluter than mineral spirits, so you may want to use it if you used a dark pigmented paint.

There is a version of turpentine that does not smell so bad, but it is said that the stronger the smell, the more efficient.

Any of these chemical products should be used in a well-ventilated room.

They are safe, but they require some precautions, as their components can cause intoxication, dizziness or respiratory irritation after being exposed to them for a long time or in a high concentration.

How to clean polyurethane brushes with turpentine

How to clean polyurethane brush with gasoline?

Gasoline might be the most unexpected element in this list, but it is still not such a weird idea.

Considering mineral spirits are made out of a petrol distillation, it’s not surprising that gasoil can also work as a cleanser for brushes used with polyurethane.

Besides, gasoline is commonly used by mechanics to clean grease out of surfaces and even their hands, so it’s normal you can also clean oil-based polyurethane paint or varnish.

However, in spite of what you want to clean with it, you always have to be very careful, as, of course, it is highly flammable. Once you have finished cleaning, wash your brushes thoroughly with dish soap.

Gasoline can leave gaseous remains on the bristles, and those should be washed off too to avoid any danger.

clean polyurethane brushes

After using these tips, those days of buying a new brush for every new project are gone! Remember to clean as soon as possible after finishing and keeping in mind what kind of polyurethane you are using.

If you want to know how to start using watercolors easily, you can see this article about How to paint water with watercolor.