How to Select and Spray Polyurethane Finish

wood varnish polyurethane finish

As you complete your woodworking projects, you will want to add a finishing coat to the wood surface for protection. This will add a layer of shine and prevent your wood material from drying out. Polyurethane is a popular choice for top coats that can be applied to wood to give it a glossy luster that is long-lasting. ​

​How to Select Your Polyurethane Finish

​There are a LOT of different types of finish you can apply to your wood. In most instances, polyurethane is the ideal protective finish for wood. ​However, lets go through the pluses and minuses of each of the common finishes

​Comparing Polyurethane to Other Finishes

Some people choose polyurethane over spray paint, polycrylic, or other finishers because it has a more durable finish that does not chip or cracks over time. In general, polyurethane is your standard "go-to" all purpose finisher. 

Polyurethane is a mix of resins and oils that provide a glossy sheen to wood surfaces. Unlike many other lacquers, polyurethane is a thicker coating that may need thinning prior to use.

There are a number of specialized finishers to compare up against polyurethane:

​Varnish vs Polyurethane

​Unfortunately, the term "varnish" is often used interchangeably to mean any type of protective finish you put on wood. However, there is a unique type of finish called varnish. 

Varnish is made up of a combination of solvents, resin, and oil. When dry, varnish has a similar look and feel that polyurethane does, including that characteristic, light-yellow tint that oil-based poly has.

In general, varnish is better used on outside wood, with polyurethane better used on wood that will be inside. Spar varnish, or marine varnish, is a specialized type of varnish that is especially great outdoors, as it has a UV protector in it.

You should also use spar varnish on outdoor wood that will be near water (think a boat dock or beach chairs).

​Shellac vs Polyurethane

​Shellac is made up from a base of insect secretion and then mixed with alcohol. Weird, huh? Shellac is all natural, which makes it a great, all-natural finish that is very safe and toxin-free. 

Shellac dries fast and adds a nice, warm sheen to the wood.

Unfortunately, shellac can be easily damaged, and does not do well around water or heat. Keep shellac off of surfaces that might experience either of these elements. It also does not respond very well to cleaning products.

Shellac is great to use on products that won't be heavily used and require a toxin-free finish. Otherwise, stick with polyurethane.

​Tung Oil vs Polyurethane

​Tung oil is a beautiful oil finish that you rub into wood as a finisher. Tung oil is unique because it soaks into the wood, rather that other finishes that just sit on the surface and dry.

As a result, you'll need a lot of tung oil in order to create a solid, waterproof finish. Tung oil is expensive when compared to other finishes like polyurethane, so it'll cost you a lot more to use tung oil.

You'll need to apply anywhere from 5-10 coats of tung oil, and it takes several days for each coat to dry. After every coat, you have to lightly sand the wood. And, you'll have to refinish your wood piece with tung oil every year. So, as you can say, it takes a lot more work. 

However, tung oil is truly the best finish to bring out the natural color, grain, and patterns of your wood.

Tung oil is best used for pieces of wood where you want the grain and color of the wood to show through. Ornate pieces such as scroll work, clocks, picture frames - pieces that won't get touched and used often.

If your surface is going to get used often, such as countertops, furniture, or flooring, stick with polyurethane.

​Oil-based vs Water-soluble

​Oil-based polyurethane needs additional time to dry but uses fewer coats per application. It is harder to clean up and releases more VOCs per use.

Water-based polyurethane takes less time to dry but needs more application coats per finish. It releases less VOCs and is easier to clean up with just soap and water.

Related: ​How to ​Apply Polycrylic

wood varnish polyurethane finish

How to Pick Your Polyurethane Sheen

​There are four finish sheens of polyurethane to select from: matte, satin, semi-gloss, and gloss. These sheens are listed in order from least shiny to most shiny. Generally speaking, sheen is a measurement of how much light is reflected back off of your surface. 

You'll need to select which type of sheen you want, but there are common applications for each. 

Matte vs Satin Finish

​A matte finish will provide the lowest amount of sheen, giving you virtually no shine to the wood that you apply it to. Satin, which is currently the most popular polyurethane finish, provides a very subtle but noticeable amount of shine. 

​As a finish, matte is rarely a good selection. Yes, it all comes down to personal preferences, and there are rare situations where it works best. But your wood will almost always look better with a slight amount of shine. Matte has a tendency to make the wood look dull. 

Lower gloss finishes, whether matte or satin, shows scratches, imperfections, and dirt much less than glossier finishes. These lower gloss finishes are also a lot easier to clean.

​Satin vs Semi-Gloss Finish

Satin and semi-gloss are actually more similar than they are different. ​When measured, these two finishes are within 15-20% of eachother for total amount of reflected light. However, you will probably notice the difference, especially if you saw them side by side. 

Our recommendation is to use satin finish for the majority of your wood surfaces, including your wood floors. Use semi-gloss for highlights, such as cabinet faces, doors, furniture, and woodwork.

Again - this is truly a matter of personal preference. Both satin and semi-gloss polyurethane finishes work well across almost all types of wood.

​Semi-Gloss vs Glossy Finish

​Glossy is a bright, shiny finish that will bring out the colors of any wood. It will also show any and all dirt, fingerprints, and scratches as well.

You can replace semi-gloss finish with a glossy finish if you want. Gloss can look good when you have really nice, ornate woodworking pieces.

Be careful to use it sparingly, and try to limit your usage of gloss finish to wood pieces that don't get much use.

How to Spray Polyurethane

Understanding how to spray polyurethane can help you finish your wood piece quickly and seamlessly. These steps can help you spray a polyurethane finish that looks pristine and professional on any wood surface.

​​Invest in the Right Equipment

Next, you need to think about how to spray polyurethane. You have the option of using a spray can or spraying polyurethane with HVLP equipment. While a spray can may seem like an efficient and easy way to apply polyurethane to your woodworking project, it can clog during use and prevent you from getting a clean, smooth surface.

Investing in an HVLP sprayer can produce a finish that is seamless and prevents spatters or runs. It is easier to hold and operate an HVLP sprayer, and the investment into the equipment will come in handy if you decide to use other finish types later.

An HVLP sprayer can be used in a variety of lacquer and varnish applications, giving you plenty of versatility with this investment.

​​Read our​ Complete Buying Guide on the Best Jigsaw.

​Prepare Your Surface

Before you begin spraying polyurethane with HVLP equipment, you need to prep your wood surface, so it will allow the poly to adhere.

Use sandpaper to smooth out your wood piece. You’ll want to start with 100-grit sandpaper and move your way down to 220 grit or finer grit sandpaper to get a soft and smooth surface to your wood.

This will help the polyurethane to stick and prevent you from asking yourself, “Can I spray polyurethane?” Yes, you can, but only once you have prepared the surface for application.

Related: ​How to Laminate Wood​​​

​Ventilate the Area

Because polyurethane gives off VOCs, it needs a well-ventilated area for application. Try to coat your wood piece outdoors. Open the windows or turn on an exhaust fan if you must spray polyurethane with HVLP equipment inside.

When spraying your poly coating, you’ll also want to take some additional safety precautions such as wearing safety glasses and a mask. Spraying polyurethane gives off a fine mist of particles that can easily go in your eyes and mouth. To prevent this risk, don the right safety equipment to ensure you are protected.

​Start at One End of the Surface

Now, you are ready to begin the application process. Get your sprayer ready to apply polyurethane at one end of your wood piece. You will work your way across the piece in a left-to-right pattern that uses a small amount of overlap.

Overlap is important as it provides full coverage of the polyurethane as you apply it. You need to be careful of your total overlap area as too much overlap can cause uneven coating of the polyurethane while too little overlap can miss spots.

Keep your coverage even and ​apply lightly, moving slowly as you spray.

Related: ​How to Stain Plywood​​​

​Perfect Your Application

Keep your HVLP sprayer level as you work. You may be tempted to use an arcing motion, but this will only create an inconsistent application of the polyurethane. You want to apply a thin, even coat of poly with each application.

You need to continually move the sprayer along as you work. Do not spend too much time in one area as you will develop runs that will ruin the finish of your wood project.

As you apply the first coat of polyurethane, if done right, you will have a light coat of the finish on your wood piece. It may not be uniform or provide complete coverage, but you will apply additional coats that will even out the appearance later.

It is always best to apply too little of the poly coating to your wood surface than too much. Too much polyurethane can be difficult to work with and prevent you from getting an even coverage that looks uniform when completed.

Related: ​Polycrylic vs Polyurethane: What are the Differences and When to Use Each​​​

glossy wood finish polyurethane

​Apply Multiple Coats

You will need to allow your polyurethane finish to dry before you are able to apply additional coatings. Keep in mind that oil-based polyurethane may take up to six hours to dry, depending on the product and how thickly you applied it. Water-based polyurethane will dry at a quicker rate of about two to three hours.

Once your first coat of polyurethane is dry, get ready to apply a second. You will need to use the same technique you used in the first application. Use a steady, level hand and apply a thin coat on the second pass.

You will need to repeat this process two to three times, depending on the desired look you are trying to achieve. Let it dry thoroughly after each application and when completed.

​​Read our​ ​Step-by-Step Guide on ​how to build your own
DIY Dining Room Table.​

​Common Polyurethane Questions

​How Long to Let Stain Dry before Applying Polyurethane?

​A common mistake to is not wait long enough in between coats of polyurethane. You need to make sure to let your ​stain dry thoroughly before applying ​polyurethane. 

The reason for this is because you ​don't want the polyurethane solvent to react with your stain. If your stain isn't completely dry, it is still susceptible to react to the chemicals that are in the poly application.

Always read the instructions for your specific stain, as they will tell you how long to wait. Generally, 24 hours is a good rule of thumb.

Keep the area where your stain is drying well ventilated to help it dry faster. Stain dries faster in lower humidity as well.  

​How To Thin Polyurethane?

​A super simple way to thin polyurethane is to use mineral spirits. 

There are a lot of myths floating around about how to thin polyurethane, and the benefits it provides for bonding. To be clear, most of these myths are untrue, and thining poly does not create a stronger bond.

Thining your polyurethane does give you several benefits. For starters, the polyurethane will dry faster. So, if you're in a hurry, this is a good way to speed the process up. 

Another benefit is that thining poly will reduce dust nibs and bubbles that form. This is due to the same reason as #1 - the poly dries faster. Faster-drying polyurethane doesn't create as many bubbles on your surface.

For this reason, we recommend thining out your final coat of polyurethane, to help reduce the number of bubbles that form. 

​​How Many Coats of Polyurethane are Necessary?

​Its worth starting by saying "it all depends on your personal preference". There is no fixed number of coats that is perfect. With that being said, here are some guidelines to follow:

  • Always apply at least two coats of water-based polyurethane, and at least three coats of oil-based polyurethane.
  • When applying to high traffic areas such as wood floors, use 4-6 coats of polyurethane.
  • More coats of polyurethane will give you more protection, but will also give you more shine and "stick".
  • If you opt to thin one or several of your coats, then you will need more coats for full protection.
  • There isn't a number of coats you reach that are "too many." However, after several coats, each subsequent coat of polyurethane has a reduced effect.

​How Long for Polyurethane to Dry?

It generally takes polyurethane 2-6 hours to dry, depending on a variety of factors, such as how many previous coats you have, temperature and humidity of the area, and a few other things.

Here are instructions from Minwax for their fast-drying polyurethane, to give you an idea what they recommend:

Recoat within 2 hours of application. If unable to do so, wait a minimum of 72 hours, then lightly sand and recoat.

Sanding with a very fine sandpaper takes out the bumps, air bubbles, and imprefections that develop during the drying process. Don't ever sand your final coat of polyurethane.

​As an aside, don't mix up drying time with how long it takes polyurethane to cure. The curing process takes several weeks. If the polyurethane is still giving off any smell, then its still curing. 

​How Long do Polyurethane Fumes Last?

​This is similar to the previous observation, as the fumes are directly related to the polyurethane curing. 

As a rule of thumb, count on it taking 30 days for the polyurethane to fully cure and stop emitting those awful (and toxic) smells. The fume smell should start to disapate within 10-14 days of application. 

​Low humidity and a temperature as close to 70 degrees as possible will help it cure faster. Good ventilation also helps, so open up the doors and windows and put on as many fans as you can.

​How to Get Polyurethane Off of Your Hands?

​For starters, try to wear rubber gloves when applying polyurethane. This will keep this issue at bay. However, if you still end up with polyurethane on your hands, start by rinsing with mineral spirits. 

Rinse the mineral spirits off, and scrub your hands with lava soap. You might need to do this process several times.

When you've removed all of the urethane, lightly soap and rinse your hands one last time.

Conclusion

You’ve now completed the spray application of polyurethane for your wood piece. These steps on how to spray polyurethane make the process simple and straightforward, so you can continue to apply it to any wood surface you are working with.

Spraying a poly coating on your wood projects will help protect them, keep them from damage, and extend their lifetime.  

​Check out our other related ​How To Guides

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