How to Apply Polyurethane without Bubbles on Your Project

You can finally show your hard work to family and friends when the final coat of water-based polyurethane is applied.

Bubbles appear in the product after completing the topcoat; what did you do incorrectly, then? You must fix it or at least know the preventive measure so that the next project does not suffer the same fate.

Applying thin coats of water-based polyurethane with a synthetic brush is the best way to avoid bubbles.

Mineral spirits should be used to thin oil-based polyurethane, and water should be used to thin water-based polyurethane.

Also, don’t try to apply water-based polyurethane with a roller or foam brush. It’s best to use a paintbrush with bristles or a spray gun To keep the paint from bubbles.

Make the application even more subtle by thoroughly wetting the brush. You do not shake the can, but instead, stir the poly.

If you see bubbles after you’ve put on the polyurethane finish, gently tap on them with the top of your brush until they flatten out. This works only before your paint is dry. After it dries, tapping won’t help.

After the polyurethane finish has dried, if you see bubbles in it, the only thing you can do is sand until the bubbles go away and reapply the polyurethane coat in the right way to avoid bubbles.

What causes bubbles in water-based polyurethane?

Bubbles will only form in the polyurethane paint if you don’t do the right prep work or use the wrong painting tools.

Shaking is not suggested for any woodworking supplies; always recommend stirring. Polyurethane with a water-based compound is different from spray paint.

Using a brush to puncture bubbles on the surface of a product will cause them to dry on your project.

You may question where air bubbles originate from. What’s creating these them is simple. Air pockets are where they come from, and you need to wet the brush before using the solvent.

Below are some reasons that cause bubbles in polyurethane:

  • Using a foam roller: As you roll the paint over the surface, air bubbles become trapped in the polyurethane covering.
  • When you paint over a porous surface, like new wood, tiny air pockets are usually trapped in the wood grain.
  • When you use polyurethane that has gone bad, bubbles form in it.
  • Apply too much polyurethane.
  • Use the wrong brush when painting with polyurethane.
  • Apply polyurethane over a moist area, and the paint may develop bubbles.
  • Overbrushing the polyurethane.
  • The polyurethane paint might have bubbles if you don’t leave enough dry time between coats.

How to apply polyurethane with no bubbles

You start by getting rid of all dust on the wood surface. It should be the floor or any furniture.

It is possible to accomplish this in two ways. A vacuum cleaner is used in the initial step.

When you are done working on the surface, hover over it slowly to remove all of the dust.

You should never attempt to apply polyurethane without first sandpapering. On the contrary, removing dust is not mandatory before sandpapering.

Sandpaper ensures that the furniture is genuinely smooth, no matter what an employee at a store tells you.

After sanding, give the wood a good wipe down. This is a useful tool for dust removal and ensuring smooth surfaces. Polyurethane will separate after keeping a long time on the storage or shelf.

You need to mix but avoid shaking the can. It is not sprayed paint because shaking produces more bubbles, making the task more difficult.

Slowly whisk it with a mixing stick or any relevant tool. The polyurethane can apply thick or thinly, depending on how thick you want it to seem.

A professional finish requires at least two coats, so thinning prevents surfaces from becoming overly thick.

For oil-based polyurethane, carefully dip the brush (synthetic or natural) into the mixture, allowing the extra fluid to fall back into the bowl. The brush should not be sprayed, and excess should not be wiped off the container’s side.

Gently stroke the wood furniture grain from one side to the other. Afterward, wait for the polyurethane to dry. For best results, give it at least twenty-four hours.

Some manufacturers recommend applying subsequent coats to improve adhesion while the first layer is still wet.

After the initial coat has cured, you must sand with 220-grit along the wood grain. Any high spots will have a smooth finish thanks to the help of sanding, which will remove air bubbles.

How to apply water-based polyurethane?

Sand your woodworking before applying water-based polyurethane. Polyurethane can be applied with a fine brush, cloth, or foam pad in a very thin layer.

You can apply water-based polyurethane using a paintbrush, or a foam applicator, by wiping it on or with a spray gun. These are 4 application methods.

Using fine-grit sandpaper, smooth down the first coat and apply a second one. Do not overdo the polyurethane and work with the grain.

A decade ago, water-based polyurethane could not even be relied upon for dining room tables. In addition to being more difficult to apply and expensive than oil-based polyurethane, these coatings were less durable.

Because of the many improvements in industrial technology, things are quite different now than they were in the past.

People have recognized that water-based solvent is significantly more environmentally friendly than oil-based polyethylene.

This product can be used on various wood surfaces due to its versatility. You may coat furniture, deck, and furniture.

When polyurethane bubbles have dried, what’s the best way to fix them?

Your finish is full of bubbles, and you are probably sobbing. If you are worried, do not be; there are some solutions available, some of which will require more effort and time than others.

Using steel wool

Dry bubbles can be removed using steel wool, and you rub the surface. If you do not add another coat, you may have to buff the entire surface to match if scratches are visible.


Begin sanding using 400-grit sandpaper or higher on the surface. This will polish your piece but also sands out any surface bubbles.

You can apply sanding on the spotted area where bubbles are located. Of course, sanding vast coverage on the surface is also possible, even recommended.

Starting all over again

If you tried the above methods and they didn’t work, you could try removing the whole layer and starting the process over again.

Working on damaged areas before you start over saves time and makes it less likely that you’ll bring more damage to the surface.

It can be hard to start over, but it is worth it.

When using water-based polyurethane, do I need to sand the surface first?

You are not compelled to perform any steps unless expressly indicated in the instructions.

With the added benefit of offering optimal floor protection, sanding sealer improves finish adhesion.

Certain water-based polyurethanes can adhere to wood floors without the aid of a primer.

Before using any polyurethane, make sure you read the instruction carefully.

Water-based products can match the strength and toughness of oil-based ones now. In the past, using water-based solvents was not feasible.

Is a single coat of polyurethane enough?

A good finish cannot be achieved with just one coat of polyurethane. Using three layers of polyurethane, you may get a high-quality finish. How many coats of polyurethane are on a different surface?

Scratches and dents will still be visible after just one layer of paint. Brush marks, bubbles, and dust nibs are common after the first coat.

As much as polyurethane flattening chemicals are designed to eliminate bubbles and marks, the first layer rarely works.

It is necessary to sand out the defects and apply at least one more layer if these issues arise. You will notice a smoother, flawless finish after applying the second layer.

How To Apply Polyurethane To Wood Floors Without Bubbles

Oil-based polyurethane helps give wood floors a new, clean look. Usually, wood floors are hard to clean after they get scratched or stained quickly.

But here are a few quick and easy ways to put polyurethane on a wood floor. Follow the given steps carefully to apply polyurethane and get the best results.

  • To start, users need paint trays, sandpaper, a long roller, etc.
  • You can use a vacuum or mineral spirits, water, and white vinegar to clean the floor.
  • Use sandpaper with a fine grit to clean the floor.
  • Now, carefully put on the first coat of polyurethane.
  • Let it dry and wait for 7 to 8 hours at most.
  • After the floor is dry, sand it with thin grit sandpaper to eliminate bubbles.
  • After sanding, use a long roller to add another coat of polyurethane to the floor.
  • Now, let dry the 2nd coat of polyurethane on the floor and wait for 24 hours.
  • Now put on the third coat, but don’t sand it yet.
  • Once you’re done, let the floor dry for up to 24 hours.

How to prevent bubbles in polyurethane?

Use a flow additive to keep polyurethane from creating bubbles. Mineral spirits can be used to thin paint or varnish that is oil-based. Do not shake the can before applying it.

To avoid or even remove bubbles from your work, you should use water- or oil-based poly, allowing adequate drying time before applying any additional layers.

Mineral spirit is useful to prevent air bubbles when rolling.

The oil polyurethane is effectively absorbed by wool rollers, which do not produce bubbles during application. With water-based polyurethane, you can use foam rollers, mohair, or microfiber.

Final Thoughts

Learning to stop something from happening, like by adding some water or using poly differently, is part of the learning process.

You can keep your polyurethane paint from having bubbles if you carefully prepare the surface before applying the paint.

You can’t use sanding to fix big bubbles in polyurethane paint. You’ll have to remove the whole coat and put the polyurethane on again.

Following these steps should help minimize the creation of bubbles and make your wood finishing projects more successful.

Frequently Asked Questions