How To Apply Water Based Polyurethane Without Bubbles In The Right Way

It all comes to the last step to apply water-based polyurethane before showing off the fantastic project to your family and friends. However, after applying the final coat on top of your product and you come back to check it out, there are bubbles! Do you start to wonder what did you do wrong? And how to apply water based polyurethane without bubbles in the right way?

The best way to apply water-based polyurethane without bubbles is to use a synthetic brush instead of a natural one to apply multiple thin coats. To make the application smoother, you can also dampen the entire brush in water. Finally, always remember not to shake up the can because it will create bubbles. Instead, stirring the poly.

In this article, I cover some valuable aspects to help you know how to apply water based polyurethane without bubbles as follows:

  • What You Will Need To Know Before Applying Water Based Polyurethane
  • Instruction On How To Apply Water Based Polyurethane Without Bubbles
  • Some Tips On How To Apply Water Based Polyurethane Without Bubbles The Right Way
  • Final Thoughts

What You Will Need To Know Before Applying Water Based Polyurethane

What Causes Bubbles In Water-Based Polyurethane

Contaminated surface

Even though you will probably do not have too many issues with contaminated surfaces when using water-based polyurethane, it still does not mean the water-based products will not cause some funny reaction to a surface. 

To prevent this, I usually strip the bare wood down or sand it down when preparing any project. Mineral spirits can also be a good idea to deep clean the wood when finishing. Although mineral spirits are solvent-based products, the best thing they can do is evaporate very quickly so you can continue with your work. They can also clean your products’ surfaces exceptionally well.

The only thing I want you to make sure when choosing mineral spirits to clean surfaces before applying any water-based polyurethane, let it dry completely first. You will receive a pretty clean surface after it has completely dried.

But if you don’t want to take any risk now and have already had some issues with bubbes, you can consider using shellac first instead of sitting there hoping, praying there will be no contamination. All you have to do is apply some thin coats of shellac, and it will seal anything underneath. After it dried, you can now use your water-based polyurethane right on top of it.

There is air in your brush

When you first see the bubbles, you might start wondering: “Where are they even coming from?” Well, the answer is more straightforward than you think: there is air in your brush that results in these tiny bubbles. Therefore, before using any product for the final coat, it is very vital that you need to make sure to wet your brush.

I usually soak my brushes under the sink with water. Yes, it is okay to wash them, but I need you to make sure to remove all the dripping water by hand before you use it. The general rule is all the bristles have to be wet, which helps them stick together and efficiently remove the air in your brush to give you a nice gliding feeling when using it.

The way to dampen the brush is pretty simple. You just need to remember to use water to soak brushes with the water-based products and use solvent-based products for the oil-based products. One significant thing I want to remind you, never to use solvent-based products with water. It will cause some severe issues in your finish, even more than the bubbles issues.

Shaking the can

The final thing I need you to remember is never shake the water-based polyurethane can. It is not the spray paint! To be honest, it is rarely recommended to shake any painting or woodworking products. Instead, stirring it to stop any bubbles from creating inside. Bubbles will form on top of your products’ surface when you shake the whole thing up, and it is also where you dip your applicator or brush in onto these bubbles. And now, you have the tiny bubbles on your dried project.

Therefore, notice this small tip from me to prevent any significant consequences later on.

What Should You Have On Hand To Begin

The items you need to prepare

  • Determination and patience: you will need them to be able to get the job done
  • A cleaning container: to clean your brush after you use
  • A storage container: some plastics can dissolve in mineral spirits, so in my opinion, it is best to have a glass container with a lid to seal for subsequent coats later on.
  • Of course, polyurethane, which is available in three sheens: gloss, semi-gloss, or satin.
  • Tack cloth: it is available online, at home centers, or hardware stores
  • Water: preferably distilled, for water-based polyurethane, or
  • Mineral spirits: for oil-based polyurethane
  • A thinning agent
  • A synthetic nylon bristle brush: for water-based poly application, or
  • A natural bristle brush: for oil-based poly application
  • A finishing brush with high quality: it is best to choose the one rated from Above Average
  • Sandpaper: for a new project: use the 120, 180, and 222 grit papers; for a re-finishing wood project: add an 80 grit to the above to better get rid of gouges, old paint, or high spots.

Some types of brushes on the market

Also, I want you to prepare some knowledge to choose the right brush to apply water-based polyurethane. I would like to ask you to forget all the cheap applicators because they will not help you have a good-result project. You want to apply water-based polyurethane without bubbles? Well, my answer is to do it the right way in the first attempt so that you will no longer need to find other solutions. And quality tools are keys to make sure you have a high-quality outcome. And of course, how to use the tools in the right way is also an essential factor.

On the market, you can find there are two basic types of brushes. 

Brushes with synthetic bristles 

Synthetic bristle brushes, most frequently made from nylon, synthetic bristle brushes are best used for water-based polyurethane as nylon repels water. With proper care, a synthetic brush with high-quality can last for a lifetime. A quality synthetic bristle brush should feel like dense natural hair.

Brushes with natural bristles 

Most brushes with natural bristles are made from ox hair which is the most common animal hair. However, not all hair is made of the same texture because the animal has their genetics, so its hair texture is different. 

The hair texture affects a lot in the finishing brushes’ quality. I heard many people praise the ox hair from Europe as the standard for making brushes. In my opinion, for applying poly, I recommend you should use a bristle brush that is a combination of hog hair and ox hair from Europe or pure Chinese hog hair. To me, hog hair is a little too stiff, and ox hair is too soft by itself to make brushes that give a truly smooth finish.

These natural bristle brushes are most suitable for the oil-based poly application, as these bristles will absorb the water-based poly you applied on the surface.

Instruction On How To Apply Water Based Polyurethane Without Bubbles

Step 1: Sanding Before Applying Polyurethane 

Before applying water-based polyurethane to your project, it will need a good surface. And sandpaper will be a helpful tool to help smooth the surface.

The sandpaper will be measured in grits, in that the coarser the paper, the lower the number of grits. Sanding really makes the chunks of wood fibers are torn out and leaves many scratches on the wood’s surface. The scratching will be more profound if the grit of the sandpaper is lower. That also means the higher grit will cause fewer scratches. To sum up, the sanding job of a new project or a re-finishing wood project is always the most time-consuming and requires the most effort part.

The sanding steps will need to start with an 80 grit paper, and once the surface is level, you can get quicker and using more higher grits in the following step. Usually, it finishes with a minimum of 180 grit paper, but preferably 220 grit. The detailed steps are 80 grit, always 120 grit, always 180 grit in advanced step, and finishing with the preferred 220 grit.

After sanding the surface, always remember to make sure that your project’s surface is dust-free before applying water-based polyurethane. Dust ruins everything! Therefore, it is best to keep your application environment free of all dust to achieve a smooth level finish of your project.

I usually use a tack cloth to wipe the dust down after using an air compressor filter with water. The air compressor is not required to remove dust and is just an option I choose to use. You also need to be cautious if you want to use the air compressor for dust removal. As I know, some models will accumulate condensation. If they express wet air, it can prevent the application of the oil-based polyurethane properly later on by driving water into the deep surface of the wood. If avoidable, I will never want my raw wood to be wet.

Step 2: Thinning Polyurethane

When going out of the container, polyurethane will become extremely hard and thick to apply on your product without any incident of running, puddling, or bubbling. It is funny that many manufacturers are advertising their products as “One coat,” which is probably too hyping. The likely to be a flaw of a product increases when the product applies in a thicker amount. I know thicker surfaces mean more protection. However, it only works best when you apply it with multiple thin coats.

That is why I always make my polyurethane thinner before applying at a 3-1 ratio: three-part polyurethane and one part of solvent. As I mentioned above, solvents for water-based polyurethane products will be water and mineral spirits for oil-based polyurethane products. The thinning polyurethane job helps a lot in making it easier to apply,  thinner the thickness, and eliminates the ability to create a puddle, run, or bubble.

Polyurethane in the storage container or a can will separate. So, you need to use a stick to GENTLY stir the polyurethane until you can feel that it does not have any lumps in the swirl or on the bottom. When you are done, prepare a separate can and make sure to pour the three-part polyurethane into it GENTLY. After that, GENTLY pour into that same container the one part of mineral spirits, and then, GENTLY mix them. I have to capitalize the word GENTLY to emphasize that this part is very important to ensure your finishing surface will not have any bubbles created when you stir the polyurethane.

Step 3: Brushing Polyurethane

I remember an old saying of the woodworkers that is still right after time to get the best finish coat: “Lay on thin.” Yes, always remember that your finish coat is to accentuate the below surface. 

Poly is a protected surface that affords more protection when the coat applied is thicker. But the best achieved to get more saving is to use many thin coats. When applying the finished coat, especially when applying water-based polyurethane, laying on thin is a vital step to avoid running, puddling, and bubbling.

Brush preparation

Above, I have already shown you how to soak your brush in water or mineral spirits or water before using it. The rule is to make sure between your brush’s bristles, there is no air stuck in. This way also helps to soften the hairs for better application. The motion of pressing and soaking the brush down a solvent container bottom will help release air, as you will probably see the air bubbles will be out when you lightly press it down.

When you are done, remove your brush gently and dry it out by dragging it across the old newspaper gently. I know this step might take you a little bit of time, but I need you to be patient on this as it is a critical process to make sure the air will be released out of the brush. 

Laying down

It is basically the same for the procedure for all sizes of your surfaces. Firstly, dip the brush gently into the polyurethane, then let the coverage drip off while holding it over the container. Remember not to add into the brush more air by tapping it, shaking it, wiping the brush on the container, dabbing it, or any other movement.

Now, you have to lay your brush in a gentle way to the right edge of the puddle, then on the same row, drag it to the left edge. Please note that never use a tapping, dabbing, back and forth, or any other move when you apply the polyurethane to your surface or when the brush is dipping into poly. Remember these keywords: avoid runs, create puddles, and avoid creating space for air.

Secondly, you repeat the above process for the next row. Always remember to gently dip the brush in the can, let it drip without wiping, tapping, dabbing, and lay the brush on the following row from the middle, which overlaps the previous rows by at least 1/2″. Then, you drag it to the right edge slowly and gently. And finally, back to the middle, drag the brush to its left edge. Keep repeating the overlapping 1/2″ step for each row until your entire surface has been covered.


Feathering out the applied polyurethane is a vital step that you need to follow here. It is not to apply more poly or dip the brush, the process of application is now completed! Now, the next step is to feather the poly that is already laid out onto your surface. 

You need to set the brush down at the right side edge using the eight rows at the far row at the back, then slowly and gently drag the entire surface from the right to the left edge. When the first row is done, overlap 1/2″ the previous row and keep repeating doing the rest rows from the right side to the left side. This is how you apply the “lay on thin”!

Some manufacturers advertise a little too much on their “one coat” products. It is the primary reason for creating puddling, running, and bubbling on the finishing coat. And as I mentioned a lot above, applying water-based polyurethane the right way is by applying multiple thinner coats to get the desired thickness on your surface. 

It is the same procedure to apply additional coats. You just need to repeat the process above for applying the poly on your surface until you receive the thickness you want. You can find below some recommendations for coating for typical usages:

  • For stools, steps, floors, footrests: 4 coats
  • Cabinets, wet surfaces, bar tops, counters: 3 coats
  • Not regularly handling furniture: 2 coats

One more hype from manufacturers I often find on the products’ summary is between coats, there is no sanding, and you need to reapply when the surface of your product is still wet so that your next coat can adhere to the previous one. I have never been a fan of this step to follow. 

I usually apply the coats as the final step to do my project. I prefer letting my project overnight to completely dry to feel its surface and check to see whether the sheen is what I expect it to be, then I can correct it easily.

Step 4: Sanding Between Coats Of Poly

Once your product has completely dried, you must do sanding, which is very light to prepare well the surface underlying for the next applied coat. To properly adhere between layers, it is necessary to slightly scratch the surface using the 220 grit sandpaper while sanding.

And do not forget to remove all the dust after you sand the product. You can use tack cloth like the previous step, but now, you have covered the wood with some protection; it is safe for you to use a paper towel or a dampened rag.

Some Tips On How To Apply Water Based Polyurethane Without Bubbles The Right Way 

Some Other Ways To Apply Water-Based Poly Without Bubbles

In my research and experience, you can use water-based poly to apply without bubbles in four ways: use a spray gun, wipe it on, foam applicator, or use a paintbrush. I have gone into a deeper detailed review with the paintbrush way above. In this part, I want to recommend to you another alternative, which is the spray gun.

The critical key is to apply multiple thin coats to prevent bubbles. Using a brush might be the most challenging way for you to try, but I have already shown you a detailed guide to follow, so I believe it is no longer a problem for you. Using a foam applicator can give your surface a thin and nice coat too. However, this way needs you to practice a little before applying as it easily offers streaks on the surface, especially in dark paints.

There are many spray methods you can choose from, including the High Volume Low Pressure (HVLP); you can even set up HVLP using the air compressor and airless spray guns. These spray methods all offer a professional, smooth finish and these spray guns are very affordable. 

Some questions you might ask when it comes to spray guns:

  • Does using water-based poly spray guns leave bubbles?

When using the spray guns to spray water-based polyurethane, I have never had bubbles on my product. The issue only happens when I use brushes. I enjoy the most when using the spray guns because it never leaves brush streaks on the surface, which makes my finished furniture more worthy for selling. However, using a spray gun means you need to set up an area for spraying it as it will leave a mess. Compared to other ways of applying water-based polyurethane such as wiping the brush on, applicator, or by brush, this is a disadvantage you should consider.

  • Do I need to water down polyurethane before spraying?

Yes, you will need to add water to your water-based polyurethane, as it is an excellent way to avoid bubbles. However, please note that to not cause any problems to the product’s durability, you can only put a max amount of water in your poly. It is best not to thin your polyurethane by no less than 10% for your sprayer. The best thing about watering down your Polyurethane is it will give you a more excellent thin applied coat, and you will find it glides more easily.

How To Fix The Poly Finish That Has Already Dried Bubbles 

Your polyurethane finish has already dried bubbles, and are you afraid that it is too late to fix it? Do not worry too much. I am right here to support you! It is not too late as there are still some methods to fix this issue, even though some are pretty work-consuming and time-consuming.


You can try sanding your surface, and the best way to use this way to fix the bubbles is using sandpaper with a high grit, at least 400, but preferably higher. It certainly can polish off the surface of your product, and it also sands out the bad bubbles on it as well. You can sand everywhere or can directly rub the bubble surface to remove the layer, or you can even try out a sander using electricity like an orbital sander. However, sanding is always a risky thing to do here.

You can try to sand out the bubbles a friendlier way to use a sponge with the minimum at 220 grit. The sponges that can be washable can do minor harm to the surface of your product. But it does not mean you have to make them wet for better results. I suggest you avoid some low-quality sponges that are hard like rocks that can easily wreck the surface. The key here is the softer the sponge, the better result!

Use steel wool

Steel wool can really help a lot in this case. You can try to rub out the annoying bubbles starting with 0000 steel wool.

I really recommend steel wool to you because I have seen how magical it is. You will not see any scratches on your surface. Instead, the surface will become glossier, and you might need to make the rest surface shiny to match if you are not planning to add any more coats. You can try the lower line at 000 or 00 steel wool if you feel 0000 is not the right thing you need.

Restart the surface

If the bubble problems are too bad that steel wool or sanding can not help you, you might have to restart the surface. I’ve met these issues before, and even though it is painful and time-consuming, sometimes life gives you no other choices. 

You should protect the not-affected areas on your surfaces, and then on the damaged areas, use the stripper. You can stain or paint this affected surface and apply once again your water-based polyurethane. 

How To Clean Your Brush Properly

After my guide above, I hope that you have found yourself a good quality brush as a sensible investment. And as with other steps in this article, cleaning your brush is paramount. I usually clean my brushes in water for water-based products, and for oil-based products, I clean them in mineral spirits. 

Your routine should be straightforward: all of the polyurethane, or varnish, or paint, or anything has to be out of the bristles before relaxing after their jobs. 

First, you need to dab and soak your brushes, squeeze and mash them in the fresh mineral spirits or water at least three times. When you see there is no more product coming out of your brushes, then you can stop. Then, you need to wash them thoroughly with water and dish soap using a scrub to comb the bristles. Finally, you rinse the brush one more time, then hang it to dry. 

You can check out the video below to have more information on how to clean your painting brush properly

Final Thoughts

So that is all the thing you need to consider when talking about applying water-based polyurethane without bubbles. Well, I hope that you have learned many things in this article, as I have entirely given you so many ways to help you avoid and fix the bubbles on your surface when applying water-based poly. 

It is cruel to admit that polyurethane can add more protection to your product or completely ruin it with just one tiny mistake. And it is part of the learning to know more ways to avoid, like applying polyurethane in different ways or adding more water to it. Do not lose patience as furniture painting, woodworking, or any other hobby all need you to invest your time in it. In a nutshell, you might want to check out and choose for yourself the best sander for stairs if you are looking for the perfect one.

That is all for today’s article. You can leave your comments or questions below if you want to ask anything. I love to receive your feedback and always excited to answer any comments from you. I really hope my above article has helped you a lot by giving you some helpful information on how to apply water-based polyurethane without bubbles.

See you again!

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