How Do You Smooth The Final Coat Of Polyurethane?

Many people wonder, “How do you smooth the final coat of polyurethane?”

The full answer lies in this article. That means I would like to give you all you need to know to make a perfectly smooth finish on PU. Let’s scroll down!


How Do You Smooth The Final Coat of Polyurethane? A Quick Answer

There are nine main steps to have a smooth finish of PU. First, you need to prepare essential items. To get started, you have to get rid of dirty marks, clean the working areas, and wipe the project. Then, you finish the large rooms, both sides of the project, and small spaces, respectively. Lastly, sand the coat and wait for it to dry.

Why Do You Need A Smooth PU Finish?

Having a smooth PU finish is like a secret in the woodworking field for those who have not known. The reason might have its roots in the low number of people who fully understand its value.

It is an excellent way to create beautiful finishes looking like real glass. Particularly, suppose you own an old and cheap wood with ugly PU applied; buffing would save your item.

Besides, smoothing the finish means you can see no bubbles, brush strokes, or other mistakes on your wood product.

Other than that, the water-based PU is relatively harder to apply long and well on any surface. That is when you need the buffing method for the best result.

How To Have A Smooth PU Finish? A Step-by-step Guide

Once you want flawless results, stick with the nine steps below. I use those techniques for an oil-based PU product. However, you can consider trying other kinds of PU. Just keep in mind to prepare well and try your best.

1- Items required

The first two tools you have to buy are a paint roller and an orbital sander. I suggest you use the BOSCH Power Tools sander due to its flexibility, various speeds, and durability. But if it costs too much, an ENERTWIST or the Makita is also a good choice.

Plus, other materials needed for this project include pieces of sandpaper, mineral spirits, PU, wipe-on PU, 6-mil plastic sheeting, and synthetic sanding pads.

2- Remove pencil marks by sanding

After you’ve already had your luggage, let’s get started on your journey.

First, take the orbital sander and remove any marks like the pencil ones. You should draw the light pencil lines with suitable grits little by little.

For example, with open-grained and old woods like ash baby-butt smooth, you can begin to sand at 80 grit. End with up to 120 grit would give better results and save you time. For some, they try to sand to 220 grits. Unluckily, the quality of the wood is not worth their effort.

Conversely, birch, maple, or other closed-grained woods, sanding through any grit steps to 220 grits is a better option. That increases the finish’s look.

Smooth PU finish (Source: woodmagazine)

3- Keep working areas clean

You can create no good painting project once your work area is a pigsty. That means you should vacuum the floor, workbench, and the task before starting. The action prevents dust, dirt, and other factors leading to a less flawless finish.

Plus, making the place clean helps you reduce the workload overall.

What’s more, you should protect the floors and unpainted areas from spills and drips. Using the 6-mil poly would help. You can make use of the poly many times before tossing them. Hence, it is worth funding.

Also, I do not want sand and finish on the same day. That is to avoid the dust remaining in the air when I sand. For those who are more careful, taking clean pieces of cloth would cease any mistake.

4- Wipe the wood item

The next step is to take a lint-free cloth to wipe the wood. Do not use water cause that may make grains appear. Instead, the solvent like mineral spirits would help. Soak the fabric in the solvent and start to clean from on down under.

Suppose you do not have a new tack cloth, take your old cotton T-shirt would save your money. That can remove all the dust alike.

Wait for the spirits to dry and move to the next step.

5- Use a roller

Now it comes to the fun part: apply the PU. I suggest you use a roller on flat and large surfaces. Saving your time and energy is the tool’s benefit.

Plus, a roller often gives better results in eliminating puddles, brushstrokes, and thin spots compared to brushes. Besides, the coat is smoother.

When you roll the PU down, ensure the surface is fully covered.

Also, to avoid bubbles while moving, you should prepare an extra PU sprayer.

After you have done a coat, dip the roller into the mineral spirits again. Then, please keep it in a closed plastic bag for subsequent use.

You often have to apply from two to three coats. Cause the first layer of PU can easily peel off after a few hours. For instance, cabinet surfaces require around two coats and those of the tabletops need three layers for better protection.

6- Coat both sides at the same time

A few people focused on rolling the top side without even giving the bottom a quick look. The consequence is the focused-on top becomes cup, warp, or twist.

That is the reason why I suggest you finish both sides equally.

To apply the PU on both sides, coat the bottom first. Then, you should quickly paint the top’s surface. That would save more time.

Also, you might not give the bottom side a second coat. Cause when you flip the top over to paint the bottom, there might be some fingerprints, spots, or drips. That is not worth trying.

7- Finish tight or small spaces

I suggest the wipe-on poly product to coat the small or tight spaces such as legs, doors, or face frames. It is pretty easy to apply and gives you an impressive hand-rubbed look.

Keep in mind to use it once the large areas’ coat is fully dry. That is to prevent you from making any dirt on the skin.

Also, you should wear a cotton rag and a glove. Then, get rid of them when one coat is done.

Besides, the wipe-on poly coat is pretty thin. Therefore, it would be helpful if you had more coats than usual.

Maybe from four to eight layers is suitable. The drying time of the liquid is also relatively short. As a result, it often only takes a day to complete the task. Of course, you should make sure the humidity and temperature are perfect.

8- Sanding

The next step is to use sandpapers or pads to sand the surface. This stage would make sure your project is free from hair, dust motes, or drips. Plus, it helps rough the surface and prepares well for the next coat.

Suppose you meet some headstrong kinds of dust; you can sand up to 280 grits. Do not forget to use mineral spirits to wipe off the dust. Then paint another coat as usual.

Sanding the surface (Source: woodworkingclarity)

9- Let it dry

Last but not least is to wait. Put the PU-coated item in a free-dust area and let it dry in at least 24 hours.

Bear in mind to maintain the temperature and humidity balance as well as the room clean.

Take a look at this video to know more about having a flawless PU finish:

How Do You Smooth The Final Coat Of Polyurethane? People Also Ask

1- Should you sand the final coat of PU?

It depends. However, I do not sand the final coat most of the time cause I already have a smooth surface.

In case you notice the layer still has bubbles, nibs, or streaks, you might need some pieces of sandpapers.

2- Why is the PU finish rough?

There are two main reasons for the case. First, you may have put the last layer of PU in an unclean area.

Hence, the surface is full of dust motes or hair. The second reason is that you wait too long time before wiping or brushing the PU-applied area.

3- Is two layers of PU enough?

I suggest you use from three to four coats of PU for the best result. For the reason that the material is pretty easy to peel off.

But you may notice it takes a longer time to dry alike. So applying the substance is time-consuming overall.

4- How to fix not good PU?

Keeping sanding and re-applying the PU is my advice. Suppose you have a lousy coat of PU; you should sand the surface first.

Then, put a light PU coat on it. Do not forget to let the layer dry. Lastly, check if it is smooth.


In summary, above are a bit of information related to the question, “How do you smooth the final coat of polyurethane.”

The two most crucial steps you should stick in mind to successfully flatten the coat are to sand the surface and apply the PU.

Plus, keeping the surrounding areas clean and free from dust is another tip to do the project.

Hopefully, the article will help you achieve your woodworking goal in the best way.

Further Reading: 

Tags: #Polyurethane  #Closet #Brush #Coat #Primer #Waterproof #Paint #Spray #Blinds #Wood 

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