Varnish and polyurethane are two of the most popular wood finishes, and there’s hundreds of varieties of each of them on the market. Trying to decide which one to use is a one-way ticket into a wood-staining rabbit hole.
The interesting thing is that, at the end of the day, varnish and polyurethane are actually the same thing. Both finishes create a thick layer that protects wood from water, rot, fungus, UV light, and scratches. However, there are some key differences that make different formulations better suited for specific applications and projects.
In this guide, you’ll find information about the different kinds of home projects for which polyurethane or varnish are appropriate, so you can narrow it down and figure out which kind you need.
Contents [ show ]
- What Is Polyurethane?
- How to Choose a Polyurethane Type
- How to Apply Polyurethane
- What Is Varnish?
- How to Choose a Varnish
- How to Apply Varnish
- Final Thoughts
What Is Polyurethane?
Polyurethane is a synthetic resin made from chemicals to imitate natural substances. It’s a very resistant type of plastic that was developed in the 1930s. Outside of woodworking, it’s used to make plastic bags, bottles, and children’s toys. It’s very resistant and dense, making it appropriate for structures that undergo heavy use, like floors and decks.
Modern polyurethanes protect wood from heat, water, and scratches. There are interior and exterior grade options, and even some products designed for boats.
There are two kinds of polyurethane available on the market: water and oil-based. The main difference between them is mainly the aesthetic you will achieve at the end.
Water-Based
These types of polyurethane provide a clear finish, preserving the wood’s natural color. They dry faster than oil-based products —they’ll be ready in just a couple of days instead of a week. Another advantage of water-based products is that they produce less odor. However, this type of polyurethane can create dangerous fumes. Another thing to note is that they usually require several coatings to achieve the same level of protection as oil-based polyurethane products.
Oil-Based
Oil-based products are the jack-of-all-trades of the polyurethane world. There are oil-based polyurethanes for boats, indoor floors, yard furniture, you name it. These products tend to enhance the natural color of the wood, making them more aesthetically pleasing. They are perfect when you want to replicate the look of a certain wood type.
Their main drawback is that it takes several days for the layers to dry, but these types of finishes are more durable than water-based products. They are ideal for projects that get heavy use, like hardwood floors.
How to Choose a Polyurethane Type
- For projects that will get a lot of use, like floors and decks, use an oil-based polyurethane for better durability. Oil-based products are resistant but not completely rigid, meaning the layer will not break off as the wood bends, but will move with it.
- For outdoor furniture, go for a water-based polyurethane. This option has the best properties to protect against damage from water, fungus, and rot.
- To enhance the natural color of the wood, water-based products are your best bet. Be careful about the number of layers you use so it doesn’t end up being too glossy.
How to Apply Polyurethane
1. Clean the Wood
Use a damp cloth to clean the wood you’re going to waterproof. If you’re dealing with a large project, you could alternatively use a power washer to save some time. Let it dry for as long as it needs to, and make sure dust, debris, and rain don’t fall on it, as these could compromise the sealant’s quality.
2. Sand It
Applying a new mix of polyurethane on top of a pre-existing one always requires sanding. With time, wood develops imperfections and cracks that you need to sand down to improve the final look of the polyurethane finish. To get the smoothest result, use a 120-grit sandpaper.
2. Apply the First Layer
Always read a product’s label before applying it, and follow the instructions. However, as a rule of thumb, you want to apply more than one layer of polyurethane, especially if you’re working with a water-based product, because they require more layers. To apply the first layer, use a brush. If there are any spots that become saturated, just wipe them down with a rag.
4.Let It Dry
Once you have evenly applied the first layer, let it dry for however long it’s stated on the product’s label. With water-based products, you can usually apply subsequent layers right away, but with oil ones, it’s better to let the oil soak into the wood for a day or so before applying a new layer.
What Is Varnish?
Varnish is a general term used to label many types of synthetic sealants, including resins, solvents, and polyurethane. The common denominator among these types of finishes is that they all form protective films around the wood. They offer protection against UV light, heat, sunlight, water, and scratches.
In its most basic form, varnish is made out of an oil, a resin, and a solvent. Because of the wide variety of products out there, there’s not one single aesthetic that describes all varnishes. It all depends on what type of look you’re going for.
Most of these products come in single cans but it’s not uncommon for them to include a catalyst that you need to mix.
There are many types of colored varnishes, but since tints don’t penetrate wood, tones can suffer from wear with time. For this reason, you should always aim to apply more than two layers of varnish when finishing wood.
The Most Common Types of Varnish Include:
- Resins
- Shellac
- Alkyd
- Lacquer
- Polyurethane
- Acrylic
How to Choose a Varnish
Since there’s an overwhelming and downright confusing number of varnishes, picking one may be difficult. Thankfully, unless you’re a professional, companies have taken care of this by clearly labeling varnishes based on not just their formulations but also on the best applications to use them for. More often than not, cans of varnish will explicitly say what they’re meant for. However, for a better general idea, here’s a breakdown of what each type accomplishes.
Resins
Resins are one of the essential ingredients of varnish, although by themselves they’re more of an aesthetic cover rather than anything practical.
Shellac
Shellac is a “spirit varnish” that’s often mixed with a catalyst. It offers a clear finish, exposing the grain of the wood. It provides minimal water resistance, and for that reason, is better suited for indoor use.
Alkyd
This is the most common type of varnish you’ll find in paint and hardware stores. It’s usually just labelled as “varnish”. Alkyd is made with a synthetic resin and mixed with an oil. It’s usually a clear finish that offers good protection against sunlight, water, and temperature changes.
Lacquer
This finish is often used in industrial operations because it’s one of the fastest to dry. This product has a wide range of uses for larger-scale projects.
How to Apply Varnish
1. Clean the wood
Use a damp cloth to clean the wood before you get started with the varnish. Using a power washer is also a great option if you’re dealing with a large project. After giving it a good wash, let the wood dry, but be mindful about dust or debris falling on it.
2. Sand It
Always sand wood before applying any type of product on it. Use a 200-grit sandpaper to get rid of any imperfections or cracks. The easiest way to accomplish a good sanding is to work your way along the grain of the wood.
3. Use Thinner
If you’re using oil-based varnish, you may want to thin it slightly with some mineral spirits like turpentine or paint thinner. Follow the products instructions to know exactly how much varnish and solvent you need to mix. Remember that you are going to apply several layers, so don’t worry about going overboard with it.
4. Apply the Varnish
Apply the varnish to the wood with a brush. Just like with the sandpaper, work your way along the grain of the wood. Once you have a applied a thick layer, let the first layer dry for a couple of hours.
5. Apply More Layers
Once it’s dry, sand the wood again. It’s recommended you do this process two or three times. However, make sure it’s dry enough to sand it, otherwise It’ll get messy.
6. Let the Last Layer Dry
Apply the last layer of varnish, and let it dry for as long as the product label says. Make sure the room where you’re storing your project is well-ventilated as varnish can produce dangerous fumes.
Final Thoughts
Woodworking is by no means a simple hobby, and looking for information about the vast number of finishes is not a straightforward job, especially when all these products are so similar. However, it’s gratifying, and there’s nothing better than seeing something you built last for years with a nice and elegant coat of polyurethane or varnish on it.
FAQs
How can you tell the difference between varnish and polyurethane? ›
While polyurethane is water- or oil-based plastic resin, varnish is older and made from resins, oils, and solvents. Because of the higher ratio of solids, varnish is less susceptible to ultraviolet light damage. This protection makes varnish an excellent choice for projects such as outside decks and exterior furniture.
Which is better polyurethane or varnish? ›Varnish works well for exterior finishes on decks and patio furniture. Polyurethane works better on wooden surfaces that are indoors. While varnish is durable and inexpensive, it's best suited for softer woods. Polyurethane dries quicker and requires fewer coats but won't hold up in the outdoors.
Is polyurethane more durable than varnish? ›Polyurethane is more durable and protect against scratches. Water-based polyurethanes dry very quickly and have a low toxicity level, making these products ideal for DIYers who don't want to deal with safety equipment or be left vulnerable to bad weather if working outside.
What are 2 disadvantages to using varnish as a wood finish? ›| Advantages | Disadvantages |
|---|---|
| Can be applied without a mask | Can stain the wood if they're not applied appropriately |
| Preserve the natural colour of the wood | Harder to apply in the summer |
| Have an anti-yellowing UV filter | Water-based urethanes can be catalyzed |
Under most circumstances, a varnish product can be applied over a polyurethane coating. It is very important to test in a small, inconspicuous spot to see if the varnish achieves the desired result, and forms proper adhesion to the polyurethane.
Can you put polyurethane over varnished wood? ›If you mean a polyurethane varnish over a traditional resin varnish, yes, you can. However, it is a good idea to scuff-sand thoroughly and get the sanding dust off before doing that. In addition, to be more sure about adhesion, coat the surface with a dewaxed shellac and then coat with the polyurethane.
What are the disadvantages of polyurethane? ›- Poor thermal capability.
- Poor weatherability.
- Attacked by most solvents.
- Utilize toxic isocyanates.
- Flammable.
Polyurethane wood finish is used to coat surfaces, protecting them from scratches and helping to resist water damage. Learning how to apply polyurethane can give wood furniture and flooring a glossy, smooth finish while improving its durability.
What is the toughest varnish for wood? ›Polyurethane is a totally man made set of synthetic organic compounds first invented in World War II. It is a polymer (poly = many, mer = part) made from the reaction of diisocyanate with a diol. It is arguably the hardest & most durable of all topcoats.
How many years does polyurethane last? ›Gloss oil-based varnish, polyurethane and Danish oil can last 10 or 20 years, though satin finishes and stains may fail sooner as pigments and flattening agents disable the driers. Water-based coatings and paints can also be viable longer than three years.
What is the toughest polyurethane finish? ›
Water-based polyurethane finish is the best polyurethane for hardwood floors, and many consider it the future of polyurethanes. High-level water-based polyurethane is as durable as oil, easier to apply, and better for you, your family, your pets, and the environment.
Which varnish is most resistant? ›Oil varnish:
Hard resins such as amber, copal etc are used which makes this type of varnish most durable.
The thicker the coating, the more solvent is trapped and the longer it stays tacky. (Varnish applied too thickly may retain a slightly tacky feel even after it has completely dried.)
How many times should you varnish wood? ›How many coats of varnish should I apply? You can apply as many subsequent coats of wood varnish as you need, but an additional two or three coats is the standard. Remember to tip-off and gently sand between each coat.
Why is varnish still tacky? ›A: Usually when varnish remains persistently sticky it's the result of application in a humid or cold environment. Sticky varnish can also be caused by too-thick application, or by re-coating an insufficiently dry layer. Traditional varnishes made in-studio (e.g. damar and mastic) are most prone to stickiness.
What is the best thing to use to put polyurethane on wood? ›Water based polyurethane can be applied with a synthetic bristle brush, foam brush, rag (if it's the wipe on type), or a spray on finish. My favorite tool to apply polyurethane (both oil and water based) is a foam brush because it's very easy to use and leaves a beautiful finish!
Does polyurethane need sanding between coats? ›Allow each coat to dry fully. To give the subsequent poly layers something to bond to, sand lightly between coats with 320-grit sandpaper wrapped around a hard block. Note: The first coat needs the most sanding to appear smooth; don't worry if it doesn't look as flawless as you'd like at first.
Is one coat of polyurethane enough to seal wood? ›The number of coats you'll need to apply will depend on several factors including the types of polyurethane, your desired appearance, and the level of protection you want. In general, it's wise to apply at least 2 coats of polyurethane to any wood surface, but it could require as much as 5 or 6 for some surfaces.
What happens if you don't put polyurethane over stain? ›While staining creates a rich, deep color that highlights natural wood grain, it does not provide long-term protection. Without a protective top coat, wood can be damaged easily due to contact with water, food, or sharp objects. A polyurethane top coat protects the wood from scratches, stains and water damage.
Does varnish penetrate wood? ›It is known that varnish does not specifically penetrate into the wood. It is the other way around. The first coat of varnish practically blocks the wood surface to supply added protection from unwanted moisture.
Should you polyurethane both sides of wood? ›
Not at all. In fact, all the evidence points the other way – that it doesn't make any difference whether the wood is finished on both sides or not. It will warp or not warp totally independent of how it's finished, because a finish only slows moisture exchange.
What will damage polyurethane? ›Most standard cleaning solutions contain either an alcohol or ammonia base, which over an extended period of time, can eat through the finish. At Grain Designs we also use low sheen urethane finishes. Common furniture cleaners such as Pledge furniture polish, may actually damage the topcoat of your furniture.
Is polyurethane waterproof or not? ›The short answer is yes, to a certain degree. There are several factors that make some polyurethanes more absorbent than others. Depending on the physical properties and material, thermoset polyurethanes can practically have zero water absorption compared to other known materials.
Is polyurethane just plastic? ›Strictly speaking, thermoset polyurethanes are NOT considered "plastic". Instead, the long flexible polymer molecules that comprise thermoset polyurethanes make this material a true elastomer.
Is it better to brush or roll polyurethane? ›Don't use rollers or foam brushes—they create bubbles. Your brush will be easier to clean, and will go longer between cleanings, if its bristles are dipped first in mineral spirits, if you're using an oil-based poly, or in water, if the finish is water-based.
Why does my wood feel rough after polyurethane? ›Whenever water or any stain or finish that contains water comes in contact with wood, it causes the wood fibers to swell, which is called “grain raising” or “raised grain.” After the water has dried the wood feels rough to the touch, and thinly applied finishes also feel rough.
Which type of varnish should never be used for furniture? ›Types of Varnish
Spar varnish is a natural varnish formulated to stay tacky; it should never be used for furniture.
Polyurethane Wood Finish
Polyurethane wood finishes are synthetic coatings that are highly durable and water resistant, making them the best clear coat for wood protection.
Application. Give the varnish a really good stir before you start. Brush it on in the direction of the wood grain, to get the best finish you'll need 2-3 coats. Make sure you leave 1 hour between each coat.
Is it better to use water based or oil based polyurethane? ›Oil based used to be unquestionably more durable. Today though, water based polyurethane has evolved with better formulations that are equally durable as oil based polyurethane. High quality water based polyurethanes is considered by many homeowners & flooring professionals to be equally durable.
How many coats of polyurethane is enough? ›
How Many Coats of Water-Based Polyurethane are Necessary for a Project? Two coats of finish are suggested for most interior projects. When sealing floors, you should apply three coats. However, do not apply more than two coats in one day.
Which is better water or oil based polyurethane for hardwood floors? ›Durability of Oil and Water-based Polyurethane
Both floor options can be great choices to finish hardwood floors. Opinions differ on which is better because of the physical properties of each finish type. Oil-based polyurethane is softer than water-based. This makes oil-based floor finishes more susceptible to dents.
ZAR
Polyurethane provides a clear coating that can prevent scratches and other damage.
Epoxy offers higher levels of rigidity and adhesion than polyurethane, making it better suited for harder surfaces.
Why is my polyurethane not getting hard? ›If you have already applied the polyurethane and it isn't drying, you can try applying heat—for example, from a heat lamp or blow dryer. It will speed the drying, just not very much.
What are the three types of varnish? ›- Oil varnishes. These varnishes use linseed oil as solvent in which hard resins such as amber and copal are dissolved by heating. ...
- Spirit varnishes or lacquers. ...
- Turpentine varnishes. ...
- Water varnishes.
Acrylic Varnish
Its water-based design ensures a toxin-free varnishing experience and produces far less odor than oil-based varnishes. Acrylic varnish is also known for its versatility—not only can you use it for indoor and outdoor projects, but you can also use it on certain non-wood materials.
Polyurethane, varnish, and lacquer are tried-and-true sealants with excellent waterproofing properties. For best results, apply the wood finish at room temperature, ideally between 65 to 70 degrees Fahrenheit.
What is one advantage of varnish over polyurethane? ›While polyurethane is water- or oil-based plastic resin, varnish is older and made from resins, oils, and solvents. Because of the higher ratio of solids, varnish is less susceptible to ultraviolet light damage. This protection makes varnish an excellent choice for projects such as outside decks and exterior furniture.
Does varnish need two coats? ›For a very durable finish and one that needs to be very tough, say on a kitchen table, coffee table or end table etc, 2 to 3 coats of varnish should be enough on the top, with 1 to 2 coats on the legs/base. For chairs, benches, chests and other such pieces, 1 to 2 coats should do the trick.
How do you prevent brush strokes in varnish? ›
Thinning each coat of varnish with mineral spirits allows the finish to flow out more smoothly, making brush marks less likely to remain as it dries.
What grit sandpaper before varnish? ›Use 120-grit sandpaper to smooth the surface. This will help the varnish stick and will give you a smooth finish. If you removed the previous coat with sandpaper, you don't need to do this step. Thoroughly stir the varnish so it's a smooth consistency with no lumps.
Is it better to wax or varnish wood? ›VARNISH FINISH FOR ENHANCED PROTECTION
Compared to the waxed finish for wooden furniture, the protection offered by a varnish will be more durable over time. We recommend waxing especially for decorative purposes, to embellish a wooden piece of furniture while providing it with a certain degree of protection.
Sometimes the varnish doesn't cover completely evenly the first time around, so another coat will even everything out. I usually give my photorealist paintings 2 coats of varnish. I let the first coat dry for about 3-4 hours, then I gently touch the surface with my freshly-washed finger to ensure that it is indeed dry.
Should you wipe off excess varnish? ›Oil (boiled linseed oil, 100-percent tung oil and blends of oil and varnish) dries soft so all the excess must be wiped off after each coat. No built-up moisture resistance can be achieved.
Can you use a hairdryer to dry varnish? ›A hair dryer removes moisture. That's its job. At the end of the day, a blow dryer ensures a consistent varnish application, prevents frosting, and speeds up the varnish dry time.
What does a polyurethane finish look like? ›Water- Based vs.
Water-based polyurethane is clear and will remain clear overtime, while oil- based polyurethane generally has a yellow tint to it that intensifies the color of the wood overtime. Another consideration when determining which base is best suited to your needs, is what you need the finished surface for.
Polyurethane rubber or polyurethane plastic
Polyurethane (or 'PU') is so versatile and flexible: it simply is confusing. The material often looks and feels like rubber. Or like plastic. Certainly black, gray or white products can put you on the wrong track.
Because water-based polyurethane dry quickly, more coats can be applied in less time than with oil-based products. Water-based polyurethane begins milky-white in the can but dries clear.
Does polyurethane leave a shiny finish? ›Flat or matte polyurethane leaves the least shiny coating and conveys the look of natural, unfinished wood. Satin polyurethane has a low to medium sheen that helps conceal dirt and scratches, making it popular for flooring. Semi-gloss polyurethane and gloss polyurethane have a higher level of sheen and reflectivity.
What is the most durable finish for wood? ›
Polyurethane is the most durable option for indoor woodworking projects. It's highly effective at protecting cabinets, doors, furniture, and floors from scratches and abrasive damage. Polyurethane is also water-resistance and is intended to enhance the natural appearance of the wood with a statin or mid-gloss finish.
What is the disadvantage of polyurethane wood finish? ›- Poor thermal capability.
- Poor weatherability.
- Attacked by most solvents.
- Utilize toxic isocyanates.
- Flammable.
Polyurethane Wood Finish
Polyurethane wood finishes are synthetic coatings that are highly durable and water resistant, making them the best clear coat for wood protection.
There is no difference between the terms urethane and polyurethane. That might seem confusing, so here's a quick explanation. Polyurethane is a polymer. A polymer consists of repeating units that are chemically linked in a particular pattern.
Does polyurethane peel off? ›Its manufacturing process involves using recycled layers of leather bonded together before being attached to a polyurethane (PU) surface. Therefore, synthetic leather isn't something as strong and elastic as real leather, and when you stretch it too much, the PU overlay begins to peel off easily.
Does polyurethane wear off? ›Polyester and polyurethane guitar finishes are also more resistant to general wear, meaning that scratches and dings are harder to see and inflict. Poly finishes can remain shiny even after decades of use, and don't fade away in the areas that you'd typically make contact with.
Why did my clear polyurethane turn yellow? ›It is a result of leaching. Porous materials like brick, wood, and paint contain chemicals that can leach into your clear coat and yellow it. This is not due to the clear coat itself; it is due to the makeup of whatever you've sealed. Some of the chemicals that can leach are naturally present in porous surfaces.
What is better oil or water based polyurethane? ›Oil based used to be unquestionably more durable. Today though, water based polyurethane has evolved with better formulations that are equally durable as oil based polyurethane. High quality water based polyurethanes is considered by many homeowners & flooring professionals to be equally durable.
What grit sandpaper between coats of polyurethane? ›Allow each coat to dry fully. To give the subsequent poly layers something to bond to, sand lightly between coats with 320-grit sandpaper wrapped around a hard block.