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What are Polyurethane Finishes?

Polyurethane finishes leave a protective coating on treated wood.
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  • Written By: Amy Hunter
  • Edited By: Bronwyn Harris
  • Last Modified Date: 17 December 2014
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    Conjecture Corporation
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Many amateur and professional wood workers consider polyurethane finishes to be the easiest to apply and most durable of all types of wood finish. There are two different types of polyurethane finishes, water-based and solvent-based. Both leave a strong protective coat on the wood, and they each have advantages and disadvantages.

Solvent-based polyurethane finishes are the older and more established form of finish. A solvent-based polyurethane finish undergoes a chemical reaction during the process of curing. The chemical reaction leads to the polymers bonding strongly to one another. Once this process occurs, the finish cannot be broken down and dissolved in mineral spirits.

Solvent-based polyurethane does have disadvantages. As you can imagine, the fumes you encounter while working on wood with this solvent-based finish are overwhelming. It is important to work in a well-ventilated area.

Another drawback of solvent-based polyurethane finishes is that they can yellow the wood finish slightly. This will not typically be noticeable on darker colored wood, but on extremely light wood, it can cause a noticeable color change. The finish will continue to darken over time.

Water based polyurethane finishes have their drawbacks and advantages as well. The chemical reaction that causes the bonding in solvent based polyurethane is not present in water-based polyurethane. This means that the water-based finish is not as durable.

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Water-based polyurethane is, however, quick to dry and easy to clean up, as it cleans up easily with water. While you should always work in a well-ventilated area, the fumes of water-based polyurethane are not nearly as strong as the fumes from solvent based finishes.

Both water-based and solvent-based polyurethane finishes can provide a beautiful and glossy finish. Regardless of the type of polyurethane you choose, the process is similar. The most important step to creating a lustrous finish on your wood is to apply multiple thin layers of polyurethane to the wood.

To apply a polyurethane finish, start by sanding the wood. Vacuum or wipe the wood to remove all dust and lint from the piece. Apply a thin coat of polyurethane and allow it to cure. Water-based polyurethane typically takes around one hour to dry, although humidity will increase this time. Solvent-based polyurethane needs around four hours to dry.

Repeat the sanding, cleaning and application step at least three more times. For the final application of polyurethane, sand the piece with wet and dry paper. After the final coat of polyurethane has dried, buff the wood with a buffing wheel. Whether your polyurethane finishes are water- or solvent-based, this process will leave you with a high-gloss finish.

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Discuss this Article

anon122766
Post 4

It is a very useful article.

In my house, after the PU coat of gates and external doors, the applicator used wax to do the buffing to provide smooth finish. However, the wax is now started coming out in the form of fine white powder and the gates and door look very unseemly. What is the best method of wax buffing and how can it be remedied? Any suggestion is greatly appreciated. thanks. --Kannan

anon80090
Post 3

is a polyurethane finish advisable for a marble floor? I am advised not to wax my marble floor because marble cannot "breathe" under wax. Does polyurethane allow marble tiles to "breathe"?

anon72217
Post 2

Thanks a lot.

anon65635
Post 1

Good! which are the solvents for polyurethane resins to dissolve and what is the solubility.

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