It is Sanding the final Layer of Polyurethane Necessary?

We all love polyurethane as a finish on different wooden surfaces such as tabletops, wooden floors, to say the least. These formulas are everything a wooden structure owner desires to decorate and protect the uppermost parts of their respective structures. In my many years in the woodworking industry, I’ve experimented with different methods of application of poly products, some have worked perfectly, yet others fell just short of expectations. One question that most of my readers keep asking is, It is Sanding the final Layer of Polyurethane Necessary? Well, it’s the right time for me to answer this question, and here’s what I have to say:

No, it would be best if you did not sand the final coat of polyurethane. Instead, it would be best to spray it or spread it in a nice, uniform, and level way. The most important thing that you must do is sand the previous coats to create a level and even base for your final layer.

If you have to sand it, which I strongly discourage, you’ll have to use a 2000+ grit and follow it with an auto buffing compound. It would help if you let your polyurethane cure completely before doing the buffing; otherwise, you might ruin the whole thing. Usually, the curing time of polyurethane is at least 2 weeks; it can take up to 4 weeks.

How Many Coats of Polyurethane is Too Much?

Well, usually, 2 layers of polyurethane get the job done on your wooden surface. If you feel like adding, then 3 layers must be the maximum. Anything more than 3 layers of polyurethane on your wooden surface is considered more. Applying, say, 4 layers would make your surface “thick and may increase bubbles’ chances of formation.

How Do You Remove Brush Marks from Polyurethane?

It takes a lot of effort, time, and even money to do a complete project of applying polyurethane finish to a wooden structure. Such an amount of work comes with many expectations, usually to get the most seamless finish possible. Sometimes, it is frustrating when the whole thing doesn’t go to plan, and you end up with brush marks on your finish. Much as it can be frustrating and demoralizing, it’s not final because you can always remove the brush marks. So, here’s how to remove brush marks from a polyurethane finish:

• Step One

Using fine-grit sandpaper, sand down the brush marks lightly, ensuring that you apply even pressure on the entire surface that contains brush marks.

• Step Two

With the help of a soft cloth, remove all sanding dirt and grit traces from the surface. It is important to remove these particles because if they get caught under your finish, the whole thing gets ruined again.

• Step Three

Apply a little amount of polyurethane finish to the brush, ensuring that you wipe off any extra finish. This process will ensure that the area does not get too much finish that may be catastrophic to the whole process.

• Step Four

Follow the above step by gently applying the finish to the area you have sanded using the brush’s fewest possible strokes. You may need to use many light coats until you achieve the desired finish. You must not apply a lot of the formula to the surface. In case it appears thick, you can use a rag to wipe the thick areas until it’s level. Give your formula enough time to dry before further processes.

How Long Should You Wait Between Coats of Polyurethane?

Most people, especially the newbies, get it wrong when it comes to the amount of time required between polyurethane coats. In the process, they end up messing the whole thing forcing an unwarranted repeat of the process. So how long should you wait between coats of polyurethane?

After cleaning the wooden surface and applying the polyurethane’s initial coat, allow it at least 2 hours before recoat. If you have to wait up to 24 hours or more, ensure that you sand the surface slightly, then follow it with another coat. Apply 3 coats on a bare wood surface and 2 coats on a surface that has a finish.

How Long Does Polyurethane Take to Harden?

There are two aspects of the hardening of the polyurethane finish. The first being “drying time” and the other “ curing time.”

It takes water-based polyurethane about 6 hours to dry, while its oil-based counterpart needs up to 24 hours to dry. The curing time of both formulas can span up to 30 days or more, depending on the prevailing atmospheric conditions.

How Can I Make Polyurethane to Dry Faster?

The best way to make your polyurethane formula dry faster following application is by ensuring that you use a thin coat. Application of thin layers allows for faster evaporation of dissolved substances hence faster drying time.

Additionally, you can speed up the drying time of your formula by working in a well-ventilated room. Improved air circulation facilitates evaporation hence faster drying.

Another factor that facilitates the faster drying of your polyurethane is the type of formula you use for your projects. Using faster drying formulas such as MinWax help boost the speed at which your surface dries following application.

Why is My Polyurethane Not Drying?

Having worked with different polyurethane types over the years, I found it quite common amongst the oil-based polyurethane formulas to take longer to dry or fail to dry at all. So what could be the cause of this? Many people rush to conclude that the polyurethane formula might be bad, which is not always the case. It’s more likely that the wood you’re finishing has natural oils or you might have applied oil to the wood, and it has not dried.

The failure of polyurethane to dry normally is in the first coat because it is the one that comes into contact with the wood. Once the first coat dries, you will not experience any other problems with the subsequent layers’ drying.

Virtually all the exotic woods except the mahogany have natural oily resin to the extent that you can feel it upon touch. Your polyurethane formula contains a mineral-spirits solvent that dissolves the resin. As soon as you apply your polyurethane formula, the two mix so that the oily resin hampers the polyurethane’s drying.

You will also experience polyurethane failure to dry if you apply the formula to linseed or any other oil provided that the oil has not dried totally. If you apply poly to any surface that contains oil, ensure that the surface has dried completely for your project to be successful.

If it is the case that you have already applied polyurethane to your wooden structure and it is not drying, you can try to fasten the drying process by: 

• Opening the windows for proper air circulation in the room. Free flow of air enhances evaporation, which may boost the chances of faster drying.
• Heat the formula’s surface using a heat gun or blow dryer; these devices will help improve the drying rate of the surface.
• If the above steps are not helpful, you may be forced to strip the whole of the polyurethane using a strong solvent like a lacquer thinner or acetone; alternatively, you can use a paint stripper and start over the entire project.

Note

Before you apply polyurethane finish to any oily exotic wood, ensure that you wipe over the surface using naphtha, acetone, or lacquer thinner. These compounds will help remove the oiliness. After all the solvents or oily components dry, you can go ahead and apply your polyurethane finish.

Another solution to applying polyurethane formula to exotic woods with oily components is by applying the first coat of shellac to help “seal in” the oily resins on these woods. Shellac has a reputation for drying well on the oily exotic woods.

If you have applied oil to your wooden surface and intend to follow it using polyurethane, allow the oil on the wood to dry properly before considering applying the poly. It usually takes up to 1 week for the oil to dry well.

How Can You Tell if Polyurethane is Bad?

So, how do you tell whether or not your polyurethane formula is bad? Well, all you need to do is examine the formula. 

Check the formula keenly to see if it is clear and free of particles. If there is crud in the poly, try filtering it with the help of a cheesecloth. After filtering, brush it on a piece of wood; if the result is fine, then go ahead and use the formula.

If the poly in question is water-based and too thick, add some water to thin it (usually not more than 10 percent). Follow it by testing your thinned poly formula on a piece of wood; if the formula appears fine, then you can use it. Otherwise, it is a bad polyurethane.

Conclusion

You need to apply your polyurethane formula in the best possible way to end up with a desirable finish. Having worked with these formulas, I can boldly say that polyurethane, though easy to apply, is delicate, and a slight mistake in the application can ruin the hard work and efforts channeled towards the entire process. You must do a proper application and ensure that you are not applying to an oil surface, just to mention a few precautions. Even so,

Do You Sand the Final Coat of Polyurethane?

I’m against the sanding of the final polyurethane coat; all you need to do is to apply nice and thin layers and allow your formula enough time to dry. Sanding of the final coat may call for subsequent finishing processes, which may prove costly and time-consuming.

I hope that you have all your questions regarding the sanding of the final coat of polyurethane answered at this point. In case you have a question, opinion, or suggestion regarding this post, please share it with me in the comment section below.