How to get bumps out of polyurethane finish- professional tips

Polyurethane finish is widely used in all sorts of DIY projects. The variety of polyurethane finishes is large. The number of options for applying a polyurethane finish is great as well. Every method has its benefits and downsides. It is all about knowing, how to fix polyurethane mistakes.

In this article, we will look into different ways of applying polyurethane, discuss the common mistakes that might occur, talk about how to get bumps out of polyurethane finish, and much more. This article will be undoubtedly helpful for anyone, who is about to be applying polyurethane on a wood surface.

The main cause of bubbles in polyurethane

Let’s look into the main causes of your polyurethane finish to form bubbles.

  1. One of the main reasons for polyurethane bubbles is the can being shaken before applying polyurethane finish. You have to carefully stir it before application.
  2. Chosen the wrong brush for application.
  3. Something is stuck in the polyurethane coating while it’s drying out.
  4. The coat of polyurethane is too thick.
  5. The weather conditions aren’t suitable. It might cause air bubbles if there is too much moisture.
  6. Applying polyurethane with a foam brush.

Will polyurethane bubbles disappear on their own?

In most cases, when you apply polyurethane, the air bubbles that do get created will disappear within just a few minutes.

If the air bubbles are big, they won’t vanish on their own. What you could try doing is bursting them before the polyurethane finish is dry.

It also depends on the type of polyurethane you are using. For a water-based one, you can try using a heat gun. Sometimes it might help remove the air bubbles fast.

If you have used an oil-based polyurethane, let the polyurethane finish dry fully. Then proceed with sanding them down.

How to apply polyurethane without polyurethane bubbles?

Before starting your project, protect your floor by placing a cloth on top of it. That way you will not have any stains left on the floor surface.

So, how do you apply polyurethane without air bubbles?

Step 1 – Remove the dust particles

The bare wood surface you are going to apply polyurethane layer to must be absolutely clean. Start with a vacuum cleaner and remove the bulk of dust nibs. Once the bulk of it is gone, use a tack cloth to remove the rest of the dirt.

Step 2 – Sand down the area

Never apply polyurethane finish on a surface that hasn’t been sanded. The surface has to be as smooth as it can be to ensure that no polyurethane bubbles appear in the process.

Start with 80-grit sandpaper for the rough wooden surface of the item. It is important to cover the whole area to ensure a smooth finish.

Then take fine grit sandpaper and lightly sand to finish the job for the perfect result. Fine-grit sandpaper is usually 120-220 grit.

Step 3 – Remove the dust nibs

After a fine-grit sandpaper job, remove all the sanding dust off the surface. Take a damp cloth and clean the area. This way, you can also check whether the entire surface is perfectly smooth. If the cloth catches the wood, you will need to sand it down more.

Step 4 – Preparation of polyurethane finish

If polyurethane has been sitting on the shelf for quite some time, it can split into 2 layers. You have to mix them again, before using them. The most common mistake that can lead to polyurethane bubbles is shaking the can. Refrain from doing that.

Instead, what you can do is stir slowly until the two layers are mixed.

Look at the consistency of water-based polyurethane. If it is too thick, you have to thin it. Otherwise, you can use it just like that. Make sure you apply thin coats, to avoid bubbles.

For the perfect finish, it is recommended to apply at least two thin coats.

To dilute the polyurethane finish, you have to add any solvent base product in a proportion of 3:1. Stir slowly to avoid bubbles.

Step 5 – Apply the first coat

Choose the brush according to the type of polyurethane you have. Usually, you need a synthetic brush for water-based polyurethane and a natural bristle brush for oil-based polyurethane.

To prevent polyurethane bubbles, don’t leave the excessive finish on the side of the can and dip the brush into the can slowly. The brush strokes must be even. Don’t rush.

Take a bit of polyurethane finish onto the brush and apply slowly onto the surface from one side to the other one. It has to be thin coats to prevent tiny bubbles.

Once you have applied the polyurethane finish onto the whole area, including the sides, you have to wait a day for the finish to dry completely.

Some production companies recommend applying another polyurethane finish on top of the first one, while it is still wet. On one hand, it will give you better adhesion, on the other hand, it won’t give you a chance to remove bubbles.

Step 6 – Lightly sand the first coat of polyurethane

After the polyurethane finish is dry, it is time to lightly sand it again. Use fine-grit paper and lightly sand the entire area.

If you have big polyurethane bubbles, use rough sandpaper or even steel wool to get rid of them before applying the next coat.

Don’t apply too much pressure, as the idea is in removing polyurethane bubbles and not the polyurethane finish.

Use a tack cloth to get rid of all the dust and dirt.

Step 7 – Apply the final coat of polyurethane

The final coat has to be a bit thicker than the first one. Use a bit more pressure for the final coat of polyurethane.

Some experts recommend to apply polyurethane finish in one direction only to prevent brush marks. If you follow the grain of the wooden surface, you won’t get any brush marks whether you apply it in one direction or both directions.

Once you have finished applying the polyurethane finish, let it dry for a day.

If you aren’t happy with the final look of your project, you can always apply more layers of polyurethane finish, as long as you repeat the sanding and cleaning steps, and give it enough time to dry.

How to fix polyurethane mistakes?

It is quite common to make polyurethane mistakes when working with a polyurethane finish.

Tiny bubbles appear on the surface if the application wasn’t done correctly and the surface wasn’t prepared properly.

Luckily, in most cases, you can fix it. Follow the information below.

1. How to get bubbles out of polyurethane

The reasons polyurethane bubbles form on the surface include the wood that hasn’t been sanded properly, the incorrect application process, or the evaporation of solvent that happens sooner than the area around.

To fix polyurethane bubbles, you have to sand the affected area slightly. Then apply polyurethane finish again. If you use a foam brush, the key is to not apply too much pressure on it as when you do, the bubbles in polyurethane form.

The sanding should be done with finer sandpaper. It is important to remove any dust afterward.

You can also try to use a heat gun to remove bubbles in polyurethane. Use a heat gun on the fresh layer of water-based polyurethane until the bubbles stretch and disappear.

2. How to fix runs in polyurethane finish

While applying the fresh coat of polyurethane, you might notice drips and other imperfections.

The key is to let the layer dry fully before trying to fix the polyurethane mistakes. There is a big chance you won’t even notice anything the next day.

If there are runs left after the coat of polyurethane has dried, you can sort them out by using 220-grit sandpaper. Sand down the area to even the coat of polyurethane level and then apply an additional coat for a smooth finish.

3. How to remove polyurethane off the floor, hands, or clothing

It is one of the common polyurethane mistakes to have drops of polyurethane on the floor after you have done working on your project. It is easy to remove them as soon as you dripped polyurethane.

Use a prepared in advance wet cloth. If the drops have already dried out, you can remove them using mineral spirits.

Soak a cloth with mineral spirits and rub the area until they are gone.

If you have some polyurethane on your hands, it can also be removed with mineral spirits. Wash your hands with soap thoroughly after that.

If you have polyurethane on your clothes, they must be washed asap. Rinse it with water first, then apply mineral spirits. Keep rubbing the spot with it until the stain is gone. Then a piece of clothing can be washed.

4. How to fix uneven polyurethane finish

The common sign of the uneven finish is the dark spots and marks on the surface. Such a layer will take way longer to fully dry as in some areas polyurethane is going to be thicker. The causes of it include bad preparation of the wooden surface, bad quality of polyurethane, and improper mixing.

To fix this, you will have to sand the area with 220-grit sandpaper. Then remove the remnants and apply the second coat of polyurethane. Make sure you apply thinner coats to prevent bubbles.

Wait for each coat to dry fully before applying another one. On average, you will need three coats to get the perfect result without bubbles in polyurethane.

5. How to fix polyurethane layers separation

This problem occurs when the layers do not stick together well. This can happen over time as well. The main causes of this are the old product, unprepared surface, the wood being too oily, and the application of thick layers.

Make sure the quality of the polyurethane you are using is good and that it is within the expiration date. Prepare the item properly, including all the steps of sanding and cleaning.

To fix such an issue is possible by removing the first coat on top and applying a new coat using another polyurethane. To improve the adhesion between the layers, it is recommended to sand polyurethane after each layer before applying a new one.

6. How to fix discoloration in polyurethane

A bit of discoloration, when the polyurethane finish turns yellow, is somewhat natural and occurs over time. Such an issue affects oil-based polyurethane only. The causes include direct sunlight, excessive moisture in the air, and minerals. Fortunately, there is a way to prevent that.

Choose water-based polyurethane to prevent it from turning yellow over time. Don’t leave the piece of furniture under direct sunlight. Do not use denatured alcohol on the polyurethane surface.

To fix the discolored layer of dried polyurethane, you will have to start over by sanding the surface and applying a new layer of coat on the surface. Do not use a foam roller, and rather opt for a brush.

7. How to fix rough polyurethane finish

This problem is usually just cosmetic and only affects the look of the project. It happens when you don’t pay enough attention to the preparation of the surface. It can be the result of the polyurethane being of poor quality.

To fix this, you typically sand the top layer of dried polyurethane, and remove all the remnants by wiping it with a cloth. We suggest you apply the second coat of polyurethane using a new can of the product. Choose a water-based one to avoid other issues and imperfections.

If after doing everything above, the surface stays rough, your only option will be to remove all polyurethane wood using steel wool and apply it again.

8. How to avoid orange peels in polyurethane finish

If the end result gives you orange peels, that means you used the incorrect method of applying polyurethane. You should use a brush or spray and not a roller. If you use a roller, it might soak polyurethane unevenly, resulting in uneven layers. The orange peels also appear at very low temperatures.

To prevent this from happening, you have to use a brush for application. Move a brush in back and forward directions, so it doesn’t leave brush marks. If you only have a roller, make sure it soaks the polyurethane well. Always give each layer enough time for polyurethane to dry.

If you have happened to get such a result, to fix it, remove the second coat by sanding it down and applying another new coat of polyurethane.

9. How to fix streaking in polyurethane finish

The marks from the brush are also a known problem when working with polyurethane. It occurs when the layer dries out faster than it can disappear. When you don’t apply enough polyurethane and the layer is too thin, it results in streaking as well.

Don’t try to save money and get a decent-quality brush. Use the sanding sealer before the polyurethane application for the top result. If polyurethane is too thick, the paint thinner will help you to get the right consistency.

To remove the marks, you have to grind the top layer of dried polyurethane. Make sure you apply a new layer evenly to prevent it from forming bubbles. For the matte finish, choose polyurethane that has zinc oxide in its formula.

10. How to fix alligatoring in polyurethane finish

This term is used for the polyurethane finish that looks like alligator skin. It has a lot of cracks and the texture is far from being good-looking. That happens because of cold weather, and excess moisture in the air, you apply thick layers of polyurethane, the surface isn’t prepared the right way and also the quality of polyurethane makes a difference.

To prevent this from happening, consider what area you are going to be working in, and the weather report does matter. Check the expiration date of polyurethane before starting, and don’t forget to shake the can gently.

To sort this out, buffing of the top layer will be required. Then apply a new layer of polyurethane following the instructions above. For hardwood floors, applying multiple coats is essential.

11. How to fix cratering in polyurethane finish

This is the result of dirt getting on top of polyurethane. The dust particles have silicone in them, which causes cratering on the top layer of polyurethane.

When you work with polyurethane, make sure you remove all the dust from the area to prevent cratering from happening. The tack cloths are a must. No chemicals should touch the surface as they can also affect the way the polyurethane finish looks like.

To get rid of cratering, grind the surface, clean it thoroughly, and apply a few subsequent coats of polyurethane again. To avoid large bubbles, let each layer of polyurethane dry first.

12. How to fix scratches on the polyurethane finish

Over time, the polyurethane finish can be scratched due to daily usage. Never sand the area too rough, be gentle. Every layer of polyurethane must be thin. Wait enough time for each layer to dry before you apply another one or start using the item.

If you apply too much polyurethane, it won’t dry properly and a few issues will appear over time.

Fixing scratches is possible by removing the damaged layer and reapplying a new one, considering the steps described above.

13. How to fix blushing on the polyurethane finish

If you have noticed some white spots in the polyurethane finish, this is the indicator of the water stuck inside the layer. If you haven’t prepared the wood surfaces accordingly, the water will get through the layer if the weather changes to humid.

When working with polyurethane, apply it when the weather is dry. Always wait enough time for the layers to dry properly. Never apply too much polyurethane.

Fixing these spots is possible by grinding the damaged layer and applying another coat on top of it.

How to apply polyurethane coat? Professional tips

1. The brush you are going to be using for applying a polyurethane layer makes a great difference in the final result. With the correct brush, you won’t need to fix polyurethane bubbles later.

A foam brush is one of the best brushes for applying a water-based polyurethane coat. They are quite cheap and provide a great result you will be happy with.

2. Try to stay away from foam rollers. Improper brush preparation will cause bubbles to form in a water-based polyurethane coat.

3. It is important to apply a thin coat of polyurethane to eliminate imperfections. You will also save a lot of time as you won’t need to sand it down. Excess polyurethane always leads to bubbles.

4. If you struggle to apply polyurethane because of its thick consistency, you have to thin polyurethane before applying the next coat.

Use mineral spirits for oil-based polyurethane and just water for water-based polyurethane.


How do you buff imperfections in polyurethane?

Wait until water-based polyurethane is fully dry. Usually, it takes 24 hours. Use 220-grit sandpaper and lightly sand the area. Remove any dust and apply a new coat of polyurethane evenly.

Why does my polyurethane look bubbly?

There can be a number of reasons for your polyurethane finish to bubble. The most common one is shaking the can before applying the first coat. Make sure you gently stir polyurethane and use the correct brush for application.

How do you get bubbles out of acrylic polyurethane?

The standard procedure includes sanding the bubbles down, wiping the surface from remaining dust and dirt, and applying another coat of polyurethane.

Will a heat gun remove bubbles from polyurethane?

It is a well-known method of removing bubbles of polyurethane. You have to position the heat gun a few inches above the wooden surface. In a few seconds, the bubbles will disappear.

At the end

Before starting any project that requires the application of polyurethane, you have to know the information about this chemical. Hopefully, this article was helpful to gain knowledge about polyurethane’s properties. Our tips and tricks will be helpful to anyone who might work with this material.

If you have friends who are planning a DIY project, please share this article with them, so they also know how to work with polyurethane and how to avoid common mistakes. If you have accidentally made mistakes, follow the instructions above to fix them. If you have any questions left, post them in the comment section below.

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