Polyurethane finishes will without doubts offer your wooden surfaces amazing touch. Bubbling, however, can compromise the good look of polyurethane finish on your structure. So, it is important that you know how to get bubbles out of dried polyurethane
If you have applied polyurethane over a wooden structure in the past or at some point in your DIY projects then you must have had an encounter with a bubble problem after it has dried. so how do you go about bubble removal?
Scuffing and sanding the bubbles using 120-grit or finer sandpaper would be the first step of rectifying the bubbles issues. If the bubbles on the surface of your structure are extensive, consider sanding using a palm sander.
Wipe clean the sanding dust with the help of damp cloth.
Finish the whole process by applying a fresh coat of polyurethane finish, ensure you move the applicator gently to avoid turbulence and formation of more bubbles.
This articles will help you solve many different polyurethane bubbles related problems. So, it would be best if you kept reading.
Main Causes Of Bubbles In Polyurethane and How to Avoid Them
Everyday we talk about polyurethane bubble problems without knowing their causes, in this section, I’ll talk about bubble issues and how to solve them:
Using the Wrong Brush
For an excellent finish, you need to choose the right kind of brush based on the type of polyurethane you intend to use.
Use a brush with natural bristles (made from animal hair) for oil-based polyurethane. They carry a lot of your finish from the can to your surface and last longer. Water-based polyurethane, on the other hand, works better with synthetic/nylon bristle brushes.
If you use natural bristle brushes with water-based polyurethane, the brush’s bristles clump together and lose their shape, and they are more likely to leave brush marks behind.
Improper Brush Preparation
Before applying polyurethane onto your prepared surface, you should dampen your brush in a solvent to remove air bubbles caught between the bristles and in the ferrule.
Soak your brush in water(for water-based polyurethane) or mineral oils (for oil-based polyurethane). Soaking the brush also softens the bristles to make your application even better.
Let the brush soak until air bubbles stop coming out from the ferrule, then remove the brush and gently wring out the solvent.
You can also drag the brush across an old newspaper (gently) to dry it out, then use your brush as you usually would.
Shaking the Cans Before Application
The two most common (proven) beliefs among wood finishing painters are that you should never shake the can or wipe your brush along the side of the can to get rid of excess product.
Both activities lead to bubbles forming in the poly, and you may transfer them to the surface as you apply the finish.
How to Apply polyurethane and avoid Bubbles in the Dried Polyurethane
Clean Your Work Surface – Polyurethane accentuates all the features of your surface – including the inconsistencies. So, before applying the first coat of your finish, take some time to properly sand the area then get rid of the sanding debris using a vacuum and a tack cloth.
You can also use a cloth dipped in mineral oils(For oil-based polyurethane) or denatured alcohol( for water-based polyurethane) to wipe the surface.
Stir the Contents of the Can – Gently stirring the polyurethane before application helps get rid of gas bubbles that had formed before. Doing this reduces the risk of you transferring those bubbles to your surface and ruining your finish.
Apply Thin Coats, Gently – A polyurethane finish looks better when the finishing surface has thin coats. Thick layers tend to be uneven and are more likely to attract dust. They also take longer to dry between coats.
“Tip-Off” Each Section of the Surface – Tipping off refers to running your brush across the surface immediately after applying your finish. Do this after each new application to minimize brush marks and bubbles.
Sand Between Coats – After applying your first coat, let the poly dry entirely before applying the next layer. Sand the surface to get rid of dust or debris that got stuck there during the drying process. Then apply the next coat.
NOTE: Before sanding, test on an inconspicuous part of the surface to ensure that the poly is completely dry. If the finish “balls up” or seems wet, let it dry some more.
Getting Rid of Bubbles In Your Dried Polyurethane Finish
Polyurethane bubbles cab demoralize you after spending your time, money and other hard earned resources in finishing your wooden structure. It is therefore important that you eliminates the bubbles at the earliest opportunity possible.
Here are some of the things and precautions that you must take to ensure that you have the best finish possible.
1.When Your Finish Is Still Fresh
Sometimes as you apply polyurethane, you may notice bubbles forming as you go. To get rid of these before your varnish dries up, dab on the bubbles with the tip of your brush or brush very lightly along the surface you are finishing to flatten the bubbles.
2. After Your Finish Dries
If you miss the bubbles when the polyurethane is still fresh, you can even get rid of them after the finish has dried. Do this by sanding out the bubbles then apply a fresh coat of the product.
How to Sand Out Bubbles from Your Finish
Step One – Use 120 grit or finer sandpaper to scuff sand the bubbles. If the bubbling is extensive, you may use a palm sander. The trick here is to sand very lightly.
Step Two – Use a damp cloth to wipe away the sanding dust.
Step Three – Apply a fresh coat of polyurethane, moving the brush slowly to avoid creating more bubbles.
Moving of the brush so quick causes trapping of air between the bristles creating air bubbles that then get transferred to the surface.
Here’s How to Fix Polyurethane Bubbles:
How Do You Smooth Out Dried Polyurethane?
If you wonder whether you can sand to smooth out your dried polyurethane, then I’d like to affirm that it is okay to sand your polyurethane finish.
There are two ways that you can use to end up with a smooth polyurethane finish. They are:
- The dry sanding of the final coat involves a simple use of the sandpaper. This method is the most preferred and used by the most out there.
- Wet sanding, there’s a combined use of wet/dry sandpaper with the mineral spirits or water.
I would not recommend dry sanding to everyone, especially not beginners, as this method tends to leave scuff marks on the polyurethane.
It would help if you stayed keen not to mess up your entire work while trying to do away with the bubble. Using any scrubber with higher than 600-grit sandpaper, you will likely end with the final coat that is cloudy and scuffed.
If you must go the dry sanding way, here’s how to do it right and safely.
Sanding as a method of rectifying polyurethane bubbles is only appropriate if your surface has enough coats of polyurethane.
If your surface has a single coat of polyurethane, then it is likely that any form of sanding method will reach the wood’s bare surface, which will force you into applying the coat.
How to Dry Sand the Final Coat of Polyurethane
For you to successfully dry sand a polyurethane finish, you will need a number of tools. Some of these tools are as highlighted below.
Tools needed to Dry Sand Polyurethane Final Coat
- 600-grit sandpaper
- Sanding block
- Shop vac/Vacuum cleaner
- A Tack cloth
- Respirator/ Nose Mask
- Mineral spirits or water
The steps you should follow to dry sand over your polyurethane finish properly are:
Step 1: Vacuum Clean the Surface
You sand the final coat of the polyurethane finish intending to remove bumps, dust particles, and other forms of imperfections.
Using a vacuum cleaner helps you eliminate any present dust particles from the surface of the wood.
Ensure that you have your shop vac hovering across every inch of the space, paying close attention to the crevices in the corners, especially if you are working on a wooden floor.
If you are working on smaller surfaces like a table or a chair, you won’t necessarily need a vacuum cleaner. Instead, use a tack cloth.
Step 2: Wipe the Surface
Once you are done vacuuming your wooden surface, there are chances that some dust particles are still on the surface. You can get rid of the dust particles with the help of water or mineral spirits.
Wipe on the surface with a cotton cloth dipped in mineral spirit if you are working with an oil based polyurethane and water for water based polyurethane.
Note: You can use water to wipe both water based and oil based polyurethane finishes.
You might not need to go through the wiping process, especially if you got it right with your vacuum cleaning task.
The only thing that will want you to undertake this procedure is because it guarantees you the confidence of working with a very clean surface.
Step 3: Allow Water to Evaporate
After cleaning and wiping over your surface, you should allow it enough time to dry.
The drying time of your surface is determined by the amount of liquid/formula you applied. If you used a lot of liquid, it would take a long to dry.
As the water evaporates, inspect your surface for any form of imperfection that needs correction.
Sometimes, you will notice the dust present on the surface, making your polyurethane finish appear bad; the next step will solve this problem.
Step 4: Sanding
Dust particles characterize sanding. Considering that they will be coming from a polyurethane finish, you must have your respirator or face mask on.
The dust particles from wood are reputable for causing different health-especially breathing complications. That’s why I insist that you must protect yourself at all costs.
Put the 600-grit sandpaper on your sanding block and swipe gently at the areas with dents, bubbles, or dust particles.
You must be gentle to avoid altering the smoother sections of the finish.
Using a sanding block help improve your accuracy. Ensure that you are sanding in the direction of the wood grain.
A 600-grit is fine; however, you can still choose to use a finer grit to stop your final product from looking cloudy.
Step 5: Cleaning of the Surface
It would be best to use your tack cloth to wipe the surface. After cleaning, you should re-inspect your finish to see if there are no more imperfections.
Until you are satisfied, there’s always more to do.
Step 6: Finish With Use a Finer Grit
It would help if you went for the finer grit sandpapers at these last processes of smoothening your polyurethane finish. Ensure that you don’t, at any cost, sand against the direction of the wood grain.
Repeat steps 5 and 6 until you have a smooth polyurethane finish.
How to Wet Sand the Final Finish of Polyurethane
You must have read it before that the wet sanding option is safer for the two. There are limited chances that your surface will be scratched when you wet sand.
Even though wet sanding is considered safer, you still need to be careful as there can be bad days, especially if you are not careful.
Tools Needed for Wet Sanding Polyurethane Final Coat
- 400-grit wet/dry sandpaper
- A sanding sponge
- Shop Vac/Vacuum cleaner
- Tack cloth
- Face Mask/Respirator
- Mineral spirits or water
Steps to Wet Sanding the Last Coat of Polyurethane
The first 3 steps are similar to those of dry sanding.
Step 4: Put Some Mineral Spirits or Water In a Cup.
Quarter fill the cup with mineral spirits or water. Mineral spirit is only preferred for the oil based on polyurethane.
You can use water for both water and oil based polyurethane.
Step 5: Soak the Sandpaper or Sanding Sponge in the Water.
Dip your chosen sanding tool in the water in the cup until it soaks up, just enough.
You can have the tool soaked overnight, but that will mean that you won’t have to pour water on the polyurethane surface.
Alternatively, you can soak it for fifteen minutes and pour water over the polyurethane finish.
Step 6: Sanding the Surface
Once you have poured some little water, begin sanding the wet surface, adding water periodically.
The water you pour on the surface will help prevent the finish from becoming cloudy.
Step 7: Wipe the Surface
The water drops you keep adding to the surface may obstruct your view, making it essential to remove them often.
From time to time, wipe the surface using a clean cloth as you keep track of your finish.
If the particles on the surface of your finish are persistent, you should repeat steps 6 and 7 until you get the results you want.
Step 8: Allow It Time to Dry the Buff
Once you are satisfied that all the imperfections are over, allow your surface to dry.
It is standard that you allow it up to 24 hours for drying.
Use a lint-free rag to buff the finished surface. At this point, you will have a smooth, shiny finish.
How Many Coats of Polyurethane?
Should you apply one coat of polyurethane to your wooden surface? No! A single coat of polyurethane would not get the job done.
If you are working with a water based polyurethane, it would be best if you applied up to 5 coats for the very best outcome on your structure. Other people would go as far as applying 7 or 8 coats of water based polyurethane finish.
For the oil based polyurethane, you should apply 3-4 coats over your wooden structure. Those number of coats will give you a high gloss finish. If there are surface runs on your finish, then you add a few more coats.
Polyurethane is a versatile wood finish. Amidst its versatility, this finish is “fragile” and needs proper handling in terms of application and general interaction.
Poor handling of polyurethane can cause some health complications. In terms of wood finishing, a poorly applied polyurethane can bubble, compromising the beauty as well as services.
Bubble does occur from time to time, and it should not be a deterrent from using this amazing finish. All you need to know is…
How to Get Bubbles Out of Dried Polyurethane
All you need to remove bubbles from your polyurethane finish is to sand (wet or dry) lightly to remove the imperfections.
You should follow sanding by wiping off the surface with either a mineral spirit (oil based polyurethane) or water for both the oil based and water based polyurethane finishes.
Even as I conclude this discussion, I hope you found this post helpful to your quest of ending with a polyurethane finish with no bubbles. And that you will end up with a finish pleasing to your eyes.
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