How to Fix Polyuthane Mistakes — 17 Issues and Solutions

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If you’re unsure how to fix polyurethane mistakes, your project can quickly go from bad to worse. Using the wrong technique can worsen the mistake, leading to costly repairs or even requiring you to start over from scratch.

So to help you avoid making things worse, I’ve created this comprehensive guide to fix streaks, marks, or bubbles in polyurethane for a flawless result.

Common Problems With Polyurethane: An Overview

Polyurethane Mistakes	Solution
Dust and entrapped insects	To fix the issue, use a toothpick to remove the unwanted things and apply a new coat of polyurethane finish.
Polyurethane runs	Light brush
Blushing	Moisten a cloth with alcohol and use it to wipe the affected area.
Deeper scratches on the polyurethane finish	Sand the surface and reapply the fresh polyurethane coat finish.
Cloudy polyurethane finish	Clean the surface using mineral spirits, sand it, and then apply polyurethane finish to resolve the cloudy finish.
Cratering	Sand the surface and apply a new polyurethane coat finish.
Alligator skin	The solution to the problem is to sand the surface and apply a fresh layer of the polyurethane finish.
Streaking in polyurethane finish	Sand the surface, and then apply a new polyurethane coat finish
Orange peel effect	Smoothen it by lightly sanding and then apply a fresh polyurethane coat finish on top.
Roughness in a polyurethane finish	Lightly sand using smooth, fine-grained paper.
Polyurethane discoloration	Make it smooth by sanding and adding a new layer of polyurethane finish to make it look new again.
Polyurethane separation	Sand the surface and apply a fresh layer of the polyurethane finish
Uneven polyurethane finish	Refinish the surface by smoothing it with sandpaper and applying a new layer of the polyurethane finish.
Polyurethane puddles	Clean the surface with mineral spirits, then sand it before applying a new polyurethane finish.
Polyurethane bubbles	Sand it gently to smooth it, and apply a fresh layer of the polyurethane finish. Make sure to tap any bubbles that appear during the process.

Issue #1: Bubbling

Bubbling is one of the common polyurethane mistakes that can negatively affect the overall appearance of a finished product. It occurs when small air pockets form and get trapped within the finish as it dries.

Understanding the causes can help prevent and fix polyurethane bubbles from occurring. So, here are several potential causes of bubbles in polyurethane:

Shaking The Can of Polyurethane

To prevent the formation of bubbles during the application of polyurethane, it is important to refrain from shaking the can. Agitating the can of polyurethane can result in the entrapment of air, which manifests as unsightly bubbles when the product is applied.

Wrong Application

When applying polyurethane, using improper techniques, such as not following the direction of the grain of the wood or applying thick coats, can cause bubbles to form in the finish. These bubbles prevent the polyurethane from effectively protecting the wood from moisture outside.

Improper Brush Preparation

To ensure a smooth polyurethane finish, it’s important to properly prepare both the wood surface and the brush. This involves cleaning the wood and soaking the brush in the solvent.

It’s also important to know that air bubbles can become trapped in the finish as it hardens, particularly between dust particles and in the area where the natural bristle brush and ferrule meet.

Wrong Brush Type

If the brush type is incompatible with the coating surface, the application process may become challenging and can result in the formation of bubbles.

High Humidity

Bubbling can also be caused by high humidity in the air, leading to moisture becoming trapped in the polyurethane.

Thick Polyurethane Coats

Another factor contributing to bubbling is applying thick layers of polyurethane. A thick coat takes longer to dry, and the slower evaporation process can result in more air becoming trapped within the coating.

How to Fix Bubbles of Poly

Step 1: Stir the Poly Can Without Shaking

Before using polyurethane, stir the can gently, avoiding rapid shaking. This will ensure a consistent composition throughout the can and prevent any air bubbles from becoming trapped.

Step 2: Clean the Surface Before Poly Application

For best results, I recommend sanding the surface and wiping it down with a damp cloth before applying the first polyurethane layer.

To remove any air bubbles and prevent bubbling after application, dip the cloth in mineral oil for oil-based polyurethane and alcohol for water-based polyurethane before wiping the surface.

Step 3: Apply Thin Poly Coats

I wouldn’t advise applying thick coats of polyurethane, as they have a lengthy drying time and can create opportunities for air to become trapped during application. My tip is to opt for thin coats instead.

Step 4: Tap the Bubbles Before They Dry

If air bubbles appear after applying the polyurethane finish, gently tapping them with the top of the brush can flatten them out. However, this method is only effective when the finish is still wet, as it won’t work once it has dried.

Step 5: Dry the Poly Coats Well

If bubbles appear in the polyurethane finish after it dries, the solution is to sand the area and reapply the polyurethane using proper techniques to prevent new bubbles. Sanding between coats can also help prevent separation and promote adhesion.

Issue #2: Cloudy Finish

The occurrence of a cloudy polyurethane finish is often caused by the entrapment of zinc oxide within the layers of the polyurethane coating.

Here are reasons why a cloudy polyurethane finish can occur when applying polyurethane to wood surfaces:

How to Fix

Ensure that the polyurethane finish coat is dry.
Remove any sources of heat or flames from the surrounding area.
Use a cloth with mineral spirits to wipe the surface and remove debris and dust
Continue wiping the surface with the clean cloth until the blotches have been completely removed, and then allow the surface to dry.
Using sandpaper with a fine grit of 220, sand the surface until the cloudy polyurethane has disappeared and the polyurethane finish has been removed.
Thoroughly clean the surface, and then apply three thin coats of polyurethane finish, making sure to allow each coat to fully dry before applying the next one.

Issue #3: Scratches

Scratches on a polyurethane finish can be unsightly and can detract from the overall appearance of the surface. These scratches can be caused by various factors, including the following:

How to Fix

Step #1: Locate the Scratches

The initial step is to assess the depth of a scratch on a surface. I’ve found that deep scratches usually mean I’ll need to do a bit more sanding and finishing to get things looking good again.

Step #2: Sand the Scratched Parts

The surface should be sanded with 220-grit sandpaper or higher, ensuring not to apply excessive force during the sanding process to avoid damaging the surface.

Step #3: Clean the Area

Clean the surface well to remove debris and dust. A dirty surface can cause problems when finishing.

Step #4: Apply a Coat of Poly

Apply the polyurethane finish smoothly and evenly with a soft brush. Keep the thickness the same throughout. I usually go for thin coats and let each one dry before slapping on another. And sometimes, a bit of light sanding between coats gives you that perfect, smooth finish.

Issue #4: Uneven Finish

This is another one of the most common polyurethane mistakes. It refers to the inconsistent appearance of the finish, with some parts looking smoother or lighter and more uniform than others. There are several reasons why an uneven polyurethane finish may occur.

Let’s take a look at some of the common causes of this issue:

How to Fix

Step #1: Sand the Uneven Finish

To achieve the desired effect, utilize fine-grit sandpaper to sand the entirety of the surface. To fix this polyurethane mistake, do not apply too much pressure, as the surface can be easily marred.

Step #2: Clean The Wood Surface

Use a wet cloth to wipe the surface thoroughly and eliminate any dust or debris. Skipping this can lead to difficulties, as dirty surfaces pose issues during application and drying.

Step #3: Apply the Polyurethane Evenly

To finally fix uneven polyurethane finish, use a soft brush to apply thin and even coats to achieve a uniform finish. Let each coat dry fully before adding the next one. Personally, I go for at least three coats, and sometimes a light scuff sanding between them can make all the difference for that smooth finish.

Issue #5: Cracked Finish

At times, you might observe cracks or crazing on the surface of your wood after the polyurethane has dried.

To fix this issue, start by cleaning the surface using steel wool dipped in mineral spirits and let it dry. Next, remove the existing polyurethane and apply a fresh coat to finish the process.

Issue #6: Puddles

Puddles in a polyurethane finish refer to areas of excess material that have accumulated and failed to level out during the drying process. These pools of finish can be unsightly and can compromise the overall quality of the finish.

Here are two common causes of puddles in a polyurethane finish:

Poor Drying Time

It is important to wait for the first layer of polyurethane to fully dry before applying the next coat. Rushing the process can lead to unwanted brush marks that cannot be easily reversed.

Thick Poly Coats

Puddles can form in a polyurethane finish if thick layers are applied. This can occur when the applicator has too much finish or when multiple coats are applied too quickly.

How to Fix

Step #1: Wipe the Poly Finish with Mineral Spirits

Use a rag soaked in mineral spirits to wipe off oil-based polyurethane. For water-based polyurethane, use a damp rag for 5-10 minutes. It is essential to act quickly with water-based polyurethane as it dries faster than oil-based polyurethane.

Step #2: Sand the Wood Surface and Repeat the Process

If the surface has dried entirely, and you were unable to wipe it off, then you may need to redo the sanding natural process entirely and reapply the polyurethane coats.

However, when reapplying, it’s essential to use thin layers and allow each coat to dry completely for several days before applying the next one.

Issue #7: Peeling Finish

A peeled polyurethane finish can result from thick application layers or failure to sand or clean the wood surface. To fix this, use a paint stripper to remove the old finish, sand and clean the wood, and apply thin layers of polyurethane with sanding in between.

Issue #8: Streaks

Streaks in a polyurethane finish are visible lines or marks on the surface of the finish, indicating an uneven distribution of the material. These polyurethane mistakes can ruin the overall appearance of the finish, making it look unprofessional and subpar.

These are the several causes why polyurethane finish streaks may occur in a polyurethane finish:

How to Fix Streaks of Polyurethane Finish

To fix streaks in a polyurethane finish, screen the surface and apply a new polyurethane layer. Sand between each coat with a fine-grit sandpaper.

If you notice low gloss levels or brush streaks, apply an additional coat of polyurethane to those areas. Wait for it to dry completely before reapplying polyurethane with some sanding in between.

How to Remove Polyurethane Streaks

To remove polyurethane streaks, allow the polyurethane to dry completely. Then, gently sand the surface with fine-grit sandpaper (220 grit), being careful not to sand too much.

After sanding, clean the surface with a tack cloth or soft cloth, and apply a new coat of polyurethane using thin layers and brushing in the direction of the wood grain. Allow each layer to dry completely before applying the next. Repeat the process until the streaks disappear.

Issue #9: Orange Peel Effect

The bumpy texture, known as the orange peel effect, can happen when a roller is used instead of a spray or brush. This effect is caused by an inadequately napped roller. The orange peel effect can also be caused by extremely low temperatures.

How to Fix the Orange Peeling Effect

Allow the polyurethane to dry completely before attempting to fix the orange peel effect.
Use fine-grit sandpaper (such as 220 grit) to sand the affected areas. Be sure to lightly sand to avoid removing too much of the finish.
Clean the surface thoroughly to remove any dust or debris.
Apply a thin coat of polyurethane, making sure to level it out as much as possible.
If the orange peel effect persists, try thinning out the polyurethane with mineral spirits or another recommended thinner.
Consider using a different applicator, such as a fine-nap lambswool roller or a microfiber roller for water-based polyurethane. When using a sprayer, it is recommended to use a fan with a size of 4-5 inches and spray at a distance of 6-8 inches from the surface.
Finally, make sure to apply the polyurethane when the temperature is between 65° and 70° Fahrenheit and avoid applying it in very low temperatures.

Issue #10: Blushed Finish

Blushed finishes refer to a milky or cloudy finish on a polyurethane surface that can occur during the drying process. These polyurethane mistakes are usually caused by humidity, moisture, or cold temperatures during the application.

The following are the other possible causes for blushing in a polyurethane finish:

How to Fix Blushes on the Finish

Dampen a cloth with alcohol and gently wipe the blushed area without applying excessive pressure. Apply alcohol directly onto the blushed surface and allow it to evaporate completely.
Next, repeat the process of wiping the surface with the damp cloth soaked in alcohol until all the blushing is gone from the surface.
Smoothly sand the surface using 180-grit sandpaper to eliminate excess blushing. Keep sanding until the wood has a dull appearance.
Lastly, apply a light coat of fresh polyurethane finish and wait for it to fully dry. Repeat the process with a second coat to complete the fix.

Issue #11: Discoloration

Discoloration in polyurethane finishes refers to changes in the color or hue of the surface. Some common causes of discoloration are:

How to Fix Discoloration

Use 180-grit sandpaper to sand the discolored area until you remove the top layer of the finish.
After sanding, use a clean cloth to wipe the surface to remove dust and debris.
Apply polyurethane finish to the sanded area smoothly and evenly.
Allow the polyurethane to dry completely per the manufacturer’s instructions before applying a second coat.
If necessary, apply a second coat of polyurethane to the finished surface after the first coat has completely dried.

Issue #12: Surface Roughness

Surface roughness is a common problem that can occur when applying polyurethane. It can be frustrating to see a rough surface on your otherwise smooth surface, but you can easily learn how to fix this polyurethane mistake. One important step is to understand the causes of roughness.

Poor Surface Preparation

Inadequate cleaning of the surface before the application of polyurethane finish can result in roughness on the surface once it dries, caused by the presence of debris and dust.

Contaminated Poly Product

Roughness of the surface may result from using substandard or previously opened polyurethane products that have been contaminated with other chemicals.

Poor Sanding Between Coats

It is important to sand lightly between each layer of polyurethane to ensure strong adhesion between the surfaces and prevent roughness from occurring.

How to Fix

To fix surface roughness and restore the glossy finish, it is necessary to thoroughly sand and screen the surface properly.
Make sure to wipe the surface properly with a cloth after applying each layer of polyurethane finish to prevent the accumulation of moisture, dust, and water between the coatings.
Lastly, once each polyurethane layer has fully dried, sand the surface gently with fine-grit paper to avoid causing any damage.

Issue #13: Runs

Polyurethane runs occur when the finish is applied too thickly or unevenly, resulting in the excess polyurethane finish forming droplets that run down the surface.

These polyurethane mistakes can also occur when the finish is applied in humid or warm conditions, causing it to dry slowly and run.

How to Fix Polyurethane Runs

While brushing the surface, inspect it carefully by looking at the reflection of light on the surface. By moving your head and the wood, you can easily spot any runs or imperfections in the polyurethane finish.
To fix runs in the polyurethane finish, use a brush to remove the excess finish or move it to an area with less application.
If you notice runs in the finish after it has dried, wait until they become harder before doing a gentle sanding to eliminate them. Once the runs are gone and you’re satisfied with the results, apply an additional polyurethane coating for an improved finish.

Issue #14: Separating Issues in Poly Finish

Poor adhesion between polyurethane coat and layers is a common cause of separation in a polyurethane finish. If you observe a separation between polyurethane layers, it could be due to the following reasons:

Application of excessive layers
Poor adhesion of oily wood to the finisher
Insufficient or not lightly sanding between polyurethane coats
Failure to clean the surface between each coating
Use of expired product
Contamination of the polyurethane
Improper mixing of the polyurethane finish

How to Fix Separation of Polyurethane Finish

Step 1: Sand the Existing Surface

Sand the whole surface with a fine-grit sandpaper. Don’t sand too hard because it can damage the surface easily.

Step 2: Clean The Wood Surface

After each polyurethane layer, wait until the surface is completely dry before using a cloth to wipe away any debris and dust. This step should be performed before applying the next coat.

Step 3: Apply Poly Finish

Using a soft brush, apply a thin and even layer of polyurethane finish over the entire surface to ensure uniform thickness. Allow the first coat to dry completely before applying a second coat.

Step 4: Sand Between Poly Coats Lightly

Here’s a tip that has served me well: after each coat dries, give it a light sanding with fine-grit sandpaper—think 320 or higher.

This will provide adhesive properties to the finish and help the next coat to stick well to the previous one. I usually go for at least three coats to get that nice, durable finish. And remember, if you feel the need, a light scuff sand between coats can make all the difference.

Issue #15: Alligator Skin Polyurethane Finish

Alligator skin finishes are polyurethane mistakes that occur when the finish dries with a texture similar to the scales on an alligator’s skin. This issue can arise for several reasons, including the following:

Expired or low-quality polyurethane products.
Applying thick layers of polyurethane
Incomplete removal of the previous polyurethane coat layer leads to interconnected cracks known as crazing.
Cold weather conditions
High moisture content

How to Fix This

Use a paint scraper or sandpaper to remove the alligator skin texture and any loose or flaking polyurethane.
Sand the surface thoroughly with 220-grit sandpaper to create an even and smooth finish.
Clean the sanded surface with a tack cloth or a clean, lint-free cloth to remove any dust or debris.
Apply a new polyurethane coat using a high-quality brush or a sprayer. Be sure to follow the manufacturer’s instructions and apply the polyurethane in thin, even coats.
Once the first coat is dry, lightly sand the surface with 220-grit sandpaper to promote adhesion before applying the next coat. Repeat this process for each additional polyurethane coat.

Issue #16: Cratering Finish

Cratering is a common issue with polyurethane finishes, which is characterized by the formation of small, bowl-shaped depressions or craters on the surface of the finish.

How to Fix Cratering

Star by lightly sanding the surface to fix polyurethane finish cratering.
Use a clean cloth to wipe the sanded surface.
Follow the manufacturer's instructions to apply a thin coat of polyurethane.
Let the polyurethane dry completely.
The surface should have a smooth finish and be free of craters after drying.

Issue #17: Trapping Insects & Dust

Trapping insects and dust in a polyurethane finish is a common issue that can occur during the drying process. Insects and dust can easily get stuck in the wet finish and become embedded in the surface as it dries, resulting in an unsightly and uneven polyurethane finish.

How to Fix a Finish With Trapped Insects or Dust

If the insect lands on a wet surface, remove it using a needle or toothpick.
Apply a small quantity of finish to the area where the insect has landed.
If the insect lands on the drying surface, wait until the surface is completely dry.
After the finish has dried, use 400-grit sandpaper to gently sand the area and remove the insect.
Avoid wet sanding, as the lubricant can mimic the finish and hide the cuts.
Apply a thin coat of polyurethane finish to the sanded region and allow it to dry completely.

How to Fix Rough Poly Application on Floors

Step #1: Sand the Floor

To eliminate rough areas and achieve a smooth surface, sand the floors using 220 fine-grit sandpaper. This can be done using a handheld sander or floor sander.

Step #2: Clean the Floor

Once the sanding process is complete, it is important to clean the floors thoroughly to prevent debris and dust from getting trapped under the next layer of polyurethane.

I usually use a specialized floor cleaning tool to ensure that I get everything up. This will help ensure a smooth and even application of the next polyurethane layer.

Step #3: Apply a Coat of Poly

Use a clean brush or roller to add another layer of polyurethane on the floor. Remember to follow the instructions provided by the manufacturer about how long to wait for the polyurethane to dry before adding another layer.

Step #4: Lightly Sand the Floor Surface

After the second polyurethane coat has completely dried, use fine-grit sandpaper to sand the floor again. This will help eliminate any rough spots or bumps in the finish.

Step #5. Clean & Buff the Floor Surface

This involves cleaning and restoring the shine of the floor surface. To do this, use a special cleaner made for hardwood floors and a soft cloth or machine for buffing. If, despite your best efforts, you’re still dealing with roughness, it might be time to call in the pros. Trust me, sometimes it’s the only way to nail that perfect finish.

The Best Way To Use Polyurethane and How to Fix Other Issues

Polyurethane is a popular choice for protecting wood against moisture, weathering, and temperature variations. If you want to apply polyurethane, here are some questions and answers to help you do it effectively:

What Will Happen If You Recoat Poly Too Soon?

Let me tell you, patience is key when you’re working with polyurethane. I’ve learned the hard way that not waiting long enough between coats can result in all kinds of headaches like bubbles, an uneven finish, or even peeling. The solvents in the new coat can mix with the previous coat, causing these issues if the previous coat has not cured fully.

What Can You Do When You Applied Too Much Polyurethane?

If you apply too much polyurethane, it can become sticky. To fix this, you must remove the excess within 30 minutes of applying polyurethane.

After it dries completely, use sandpaper that’s 320 grit or finer to lightly sand the surface. This will make the finish even and thin.

Can You Put Another Coat of Polyurethane Without Sanding?

Technically, you can slap another coat of poly on without sanding, but honestly, I wouldn’t recommend it.

Sanding helps to create a surface that the next coat can adhere well to, ensuring proper adhesion between the coats. Without sanding, the new coat may not bond well to the previous coat, resulting in the peeling or flaking of the finish.

How To Repair a Damaged Poly Finish

Use mineral spirits and a cloth to wipe the damaged area and remove any dirt or dust present.
Allow the area to dry completely.
Use sandpaper with a grit of 320 or finer to gently sand the damaged polyurethane finish.
Clean the surface and wipe off any dust.
Put a thin and uniform layer of polyurethane on the affected areas while moving in the same direction as the wood grain.
Wipe off any extra polyurethane and let it dry for at least 24 hours.
Gently use sandpaper on the dried polyurethane finish to eliminate any bubbles or dust nibs.
Repeat the process until the desired results are achieved.

What to Do When Poly Isn’t Adhering to Wood

To resolve problems with polyurethane not sticking, use 320 grit or finer sandpaper to gently sand the current polyurethane finish, then wipe the surface clean and apply a fresh, thin layer of polyurethane in the direction of the wood grain.

Can You Touch Up Poly?

It is possible to touch it up as long as the mark or damage has only affected the polyurethane coat and not the wood underneath.

This is the process to touch up a polyurethane finish:

To begin the process of touching up a polyurethane finish, start by cleaning the entire area meticulously to eliminate any dust or dirt. A gentle cloth dampened with hot water or a mild cleaning solution can be used for this purpose.
After cleaning the current finish, allow it to dry completely for several hours before proceeding.
Using 220-grit sandpaper, gently sand the damaged area of the finish. It is important to be cautious while sanding to avoid removing more finish than required.
Use a foam brush or small brush to apply a thin layer of the new polyurethane finish on the sanded region, matching the shine and color of the existing finish as closely as possible.
Allow the newly applied finish to air dry completely for a period of 24 to 48 hours, following the instructions provided by the manufacturer.
If needed, use sandpaper to gently sand or buff the new finish and apply additional touch-up layers until the finished surface is smooth.

How to Buff Imperfections In Your Polyurethane Finish

To buff out imperfections in polyurethane, use a light touch when sanding with sandpaper [1] that has a grit of 1500 or finer.

How Does Vinegar Work With Polyurethane?

When cleaning wood to eliminate grime and tough residue from the surface, vinegar is frequently applied.

However, it is essential to exercise caution when utilizing vinegar to avoid harming the polyurethane finish. Here are some points to remember when using vinegar on top of polyurethane.

Dilute vinegar with water (1 part vinegar to 3 parts water) before cleaning a polyurethane finish.
Test vinegar on a hidden area first to ensure it won't damage or discolor the finish.
Use vinegar sparingly on a polyurethane finish to avoid damaging it, even when diluted.
Use a soft, lint-free cloth or sponge when cleaning with vinegar, and avoid scrubbing too hard to prevent scraping or other damage to the finish.

FAQ

Why is polyurethane not drying evenly?

Uneven drying of polyurethane can be due to insufficient surface preparation, such as incomplete cleaning or sanding. Alternatively, if a thick layer of polyurethane was applied in a single location, it could also cause uneven drying.

More about fixing tips and tricks here:

Conclusion

The process on how to fix polyurethane mistakes requires patience, attention to detail, and the right tools and techniques. Whatever the issues are, there is often a solution that can help you achieve the desired finish.

By following the 17 solutions I’ve outlined above, you can feel confident in your ability to correct polyurethane mistakes and achieve the look you want for your project.

Author
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Robert Johnson

Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You've probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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