Can You Apply Polyurethane With a Foam Brush?

Can You Apply Polyurethane With a Foam Brush

There are purists, there are corner cutters, and there are woodworkers on a budget.  Which one of those you identify with may provide an answer to this article’s question.

For some, there is only a paint brush, and nothing else will do.  These purists will insist that not just a brush but a quality brush is the only tool for applying virtually anything on a piece of wood – paint, stain, or topcoat.  

Others will cut corners, and since they have a bag of cloths in their shop, will choose something they can wipe on with them.  There is a wipe-on polyurethane product, and it lends itself well to cloth application.  Wipe-on polyurethane is merely a standard polyurethane that has been thinned out with mineral spirits.

Wipe-on polyurethane has some simple and obvious advantages:  

  • No brush marks
  • No drips
  • No more hard to reach places

So, why not grab a wipe-on poly and a cloth, and get to work?  You must dampen a clean, lint-free cloth, wipe the poly on, and wait a couple of hours for it to dry before you add the next coat.

Then, there are those on a budget who look for ways to save money anywhere they can.  A quality paint brush can cost from $25 and up.  Sure, it will do a terrific job for you and distribute paint evenly.  

Of course, you’ll have to clean it when you’re finished.  We wrote about cleaning a brush after applying polyurethane recently, and you’ll find that piece here.  Depending on the type of polyurethane you’ve used, oil-based polyurethane or water-based polyurethane, there’s a little bit of work to do with that cleaning.

Finally, we have the cheapo who looks for any way to save a dollar or the woodworker on a tight budget.  Instead of $25 and up, they’ll choose from the foam brushes rack at the local hardware store, and spend as little as $1.25 for one, or maybe by four for $5.  That will leave him with lunch money after the first coat has been applied.

As an aside, there are the show-offs who’ve invested in a spray painter.  It is, frankly, our favorite way to apply polyurethane on a finished project.  The coat is even, the application easy and fast, and the result is a smooth finish.  It also will give a more professional appearance to the finish.

It’s a good idea to thin the polyurethane for spray application.  You’ll have greater control over the spray and less chance of texture bumps.  Of course, there will be no brush marks or bubbles too.  See our thinning polyurethane for spraying piece here.

But that’s not what this article is about, s let’s talk about applying polyurethane otherwise and the best practices to consider.

Types of Polyurethane To Choose From

We’ve often written about polyurethane for a fairly good reason.  So many of us will turn to it as a topcoat for both stained and painted projects.  It forms a film, a plastic sheet, on the project that protects it from water and heat, protecting our hard work for a long time.

It’s composed of 2 main chemicals:  polymers and urethane.  Polymers may be natural or synthetic substance that is sort of like plastic; urethane is sort of rubber, somewhere between plastic and rubber, actually.  Examples of polymers include nylon, silk, and Teflon.

Together they form polyurethane.  The medium that carries them can be either oil or water in an oil-based polyurethane product or a water-based polyurethane.  Each has its own strengths and weaknesses that help you choose between the two, but most of us turn to the water-based polyurethane version – no odor, dries quickly, easy clean-up, and stands up well for a long time.

Polyurethane Application Methods

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You’ve decided on which poly product you will use on your project, and it’s time to choose an application method.  The choices are clear:

  • Bristle brush.  When it was first developed, polyurethane had to be brushed on.  Advances in chemical composition, though, now offer other methods, but we’ll deal with brushes first.  There is a greater risk of bubbles when using brush application, and sanding will be necessary between coats to remove them.  There’ll be more work with a brush application as a result.  
  • Rag.  We mentioned cloth wipe-on application as an alternative to bristle brushes.  Wipe-on polyurethanes, thinned with mineral spirits, do wipe on easily and well.  You won’t have a bubble problem with cloth applications that you could have with bristle brush application.  Be sure to exercise great care when disposing of the cloth after use to avoid the chance of combustion and fire.  Let it dry fully before you throw it away.  We wrote about this in a recent post, and you’ll find that article about polyurethane combustion here.
  • Spray.  Again, we mentioned this earlier. No need to repeat ourselves except to say it’s our favorite method of polyurethane application. 

What About Foam Brush Application for Polyurethane?

Foam Brush Application for Polyurethane

We’ll finally get to the woodworker on a budget now.  We know that a high quality bristle brush will run us $25 and up, even over $50 for a really good one.  Extra care is required for those pricey brushes to justify the expense.  We recently read a piece and watched a video about a woodworker who had brushes that were 20 – 25 years old, kept in great condition by cleaning well after every use over that span.

Again, though, work and your time is required, as well as your money.  A tightwad is looking for ways to save money and perhaps even save some work.  

Foam brushes, then, rise to the occasion.  Inexpensive and effective, foam brushes do have appeal for applying polyurethane.  They’re budget-friendly and apply polyurethane more with a wiping motion than a brushing motion.  

As such, they are closer to a cloth wipe-on method and, as a consequence, do not leave brush marks.  With foam brushes, there is less chance of drips, too.  

Additionally, they are not likely to create bubbles, either, as brushes are.  This will mean less sanding between coats, too.  

Some woodworkers prefer to use foam brushes for smaller project pieces because foam brushes tend to be smaller than bristle brushes, and bristle brushes for larger projects with a wide brush model.  However, foam brushes do come in sizes as large as 4 inches and can take on a table top well.

Smaller foam brushes will give at least equal ability to reach tight corners and awkward angles with ease, just as you can with a cloth wipe-on application, although the handle of the foam brush probably extends your reach.  They come in sizes as small as 1” up to the 4” mentioned earlier, matching a wide bristle brush choice on the upper range.  That 4” size will cover a lot of area quickly for you.

You don’t want to use a foam brush with shellac or lacquer.  The foam will deteriorate from the chemical composition of shellac and lacquer, and the application will suffer.  But polyurethane is just fine for a foam brush and will lay well with no brush marks and no bubbles.

Foam brushes have wooden handles, and gloves are not necessary when using them with polyurethane applications.  If you are concerned about getting poly on your hands, though, gloves won’t get in the way.  Blue nitrile gloves are a better choice than old-fashioned latex gloves that will eventually disintegrate from chemical exposure.  

Dip the foam brush in the container, spread the polyurethane over the wood surface, pull the brush over the just applied poly to gather any excess, and allow the polyurethane to dry.  It’s that simple.

One of the most appealing aspects of using foam brushes, no matter what you are applying (paint, stain, poly) when you are done, it’s pretty easy to simply toss that $1 foam brush.  

Cheaper, no bubbles, no brush strokes, smooth coat – a poly foam brush has a lot going for it.  And when you’re done, toss the $1 brush away.  

Just to impress upon you how easy it is to use a foam brush to apply polyurethane, here’s a short video demonstrating what we just wrote.  Notice he reminds you to pull the foam brush across the poly you just applied to remove excess.

Sure, you can apply polyurethane with a foam brush.  Why shouldn’t you, unless you’re like us and both have and prefer a spray gun.