May 5, 2022

Can I use an orbital sander between coats of Polyurethane?

Most people assume that an orbital sander is only good for sanding wood. However, when sanding wood, an orbital sander isn’t any better than a palm sander or (even) a sanding block. The secret to using an orbital sander between coats of polyurethane is to make sure you’re using a pad with dense foam and taking it slow.

What happens if I don’t sand between coats of Polyurethane

  1. There will be a buildup of dust and bubbles. These elements are inevitable and will get stuck in between the coats. With the first application of Polyurethane, bubbles will begin to form and to handle this. You need to sand each layer. Regardless of how clean the workspace is, sanding the coats down individually is essential to deal with the sanding dust and bubbles. Dust particles are found everywhere, especially in wood workshops, and sand getting stuck between layers will make the finish look unpleasant. The dirt will be permanently stuck in between finishes, and eventually, it will also cause the finish to crack. The damage will take only a few months to become noticeable. Therefore, the time taken to sand is worth it.
  2. You will experience poor adherence. Most of the coats you add after will struggle to stick efficiently to the wood. Each layer requires sanding because the coats won’t stick seamlessly with the collection of dust, bubbles, and other impurities. Instead, they will stick to the dust, which is less secure. Oil-based Polyurethane is primarily one of the finishes that requires sanding because it is slippery. It is likely that without effective layer-by-layer sanding, the chemical solvents will not bond appropriately. Oil-based polyurethane layers are meant to fuse, but when they come into contact with foreign elements like air and dust, they can sit on top of each other. The result is that the topcoat will peel off in a brief period. 
  3. Brush marks remain permanently. Not being able to remove brush marks will significantly bring down the aesthetic value of your project. Unsightly and painful errors are often fixed through sanding. Brush marks are almost inevitable regardless of the skill of the user. Polyurethane is a thick and heavy liquid; therefore, you need to sand it down and use a fine foam brush to prevent them from remaining on the finish. Light sanding and a new final polyurethane topcoat should help remove any minor imperfections. 
  4. Cracking is a common problem that results from adding several coats to a project. Too much Polyurethane will dry faster in warm temperatures, which can happen between coats. Fast drying solvents can be uneven, leaving room for moisture to enter and cause the finish to crack. Light sanding to even out the Surface combined with another skinny coat of Polyurethane will prevent the problem from occurring.

Do I need to sand between coats of Polyurethane?

Polyurethane is a fast drying agent that requires sanding to avoid the buildup of dust and bubbles. It would be best if you took the time to sand between coats of Polyurethane. Sanding will prevent the finish from peeling or cracking. Any minor imperfections are also solved by sanding. 

Can you put too many coats of Polyurethane

Uneven Layers

Adding too many coats of Polyurethane will cause you to have unbalanced layers. This uneven finish will be weaker than a finish with the appropriate amount of Polyurethane layers. The extra layers will need to be sanded off to make it even.

Yellow Look Finish

Adding an excessive amount of polyurethane coats to your finish will damage the aesthetic. It will end with a yellow look that will only worsen over time. The yellowing results from oxidation, and to prevent this, you will need to scrape off the old layers. 

Peeling

Peeling is a common problem for finishes that have too many coats. Adding too many coats will make the overall finish thicker, making it softer. Soft finishes often peel off. You will need to get a razor blade and cut off the peeling area to correct the overcoating problem. 

Increased Waiting Time

Applying Polyurethane is meant to be a fast and straightforward process. Using an excessive number of coats will lead to an extension of the process. Each coat will need its own time to dry before the next can be applied. Therefore, this result is not favorable and should be avoided to prevent damage to the product.

Overall you will sacrifice the wood you intend to protect by overcoating it with Polyurethane. Bare wood and furniture need to receive the correct number of coats to help increase their durability.

Can I use an orbital sander between coats of paint?

An orbital sander is a potent machine that is too aggressive for a coat of paint. It is unlikely that the coat of paint will require such power to handle the blemishes. Typically, 400 grit sandpaper will be enough to provide good sanding when done by hand. Using a palm sander will overshine the finish and reduce its layers. This machine will likely remove the finish rather than only shining it. 

Second coat of Polyurethane

Two coats are a sufficient amount of coating. It is strong enough to be hard and durable without peeling or cracking. It is also a manageable amount of work to do for a beginner. It will also offer you enough protection against UV rays and moisture. For areas that experience a lot of traffic, you will likely need three coats. 

Minwax polyurethane sanding between coats

The sanding procedure will help improve your finish’s adhesiveness and make it last longer. It is essential to sand between coats of Minwax polyurethane. This process will prevent bubbles and dirt from remaining in the finish permanently. See our post about the use of polyurethane with wax.

Wet sanding polyurethane

  1. You will need mineral spirits mixed with water in a cup.
  2. Soak the sanding sponge in the solution.
  3. Add water to the Surface and begin sanding.
  4. Wipe the Surface dry of any excess water.
  5. Allow the wood enough time to dry, then buff it with a dry cloth.

Sanding Polyurethane between coats

Sanding Polyurethane between coats is an important task that will help to preserve the wood and finish. It prevents bubbles and dirt from compromising the adhesiveness of the finish.

Mineral spirits between coats of Polyurethane

Mineral spirits help to thin the coat of Polyurethane. It means you can add more coats without overcoating the wood. 

David D. Hughes
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