When it comes to picking a sealant for furniture or paint, two top coats are usually at the top of every DIYers list; polyurethane and varnish. However, what’s the difference between both sealants? Here is the answer to that.
Varnish is an old finish that is gotten from the combination of resins, paint chemicals, oils, and solvents. Polyurethane however is a synthetic plastic polymer that is either water or oil-based.
Polyurethane doesn’t have as many chemicals as varnish. The main ingredients in polyurethane are polyols and isocyanates or diisocyanates. However, with varnish, there are several oils, resins, additives, and paint chemicals in the paint coating.
The extra additives and chemicals in varnish make the paint more toxic when compared to Polyurethane, especially water-based polyurethane.
But that’s not all. There is more to know about the differences between polyurethane and varnish and this post digs right into the topic. Let’s dive in.
What Is Polyurethane?
Polyurethane is plastic in liquid form. The sealant is a top choice among DIYers and painters due to its durability and strength. There are two categories of polyurethane; oil and water-based poly. Oil-based polyurethane is more durable than water-based poly but water-based poly is easier to apply.
Regardless of the type of polyurethane used, the finish is usually a thick and moisture-resistant film. This film prevents damages, dents, and moisture from damaging the paint and material underneath. The plastic-like polyurethane finish is birthed from the chemical reaction between polyols and isocyanates or diisocyanates.
There is also polyurethane designed for exterior use. This Polyurethane is designed with additives that make it UV resistant. Polyurethane is commonly used to cover furniture, exterior surfaces, and outdoor furniture. The finish can be applied by spraying, brushing on, or wiping on the material.
What is Varnish?
Varnish is an oil-based clear sealant. The word “varnish” is wrongly used as a household name for all sealants and top coats used to cover wood. However, varnish here refers to a clear top coat used to protect wood stains and material. Varnish is thick, strong, and water-resistant.
However, the sealant is dated. Varnish is one of the first wood sealants produced which is why most wood sealants are referred to as sealants. Since it’s an old sealant, the varnish is made up of several strong resins, chemicals, additives, and natural substances.
All these compounds are designed together to make the varnish paint stronger but they also make varnish more toxic. . There is also a wide range of varnish types to choose from. Each with its distinct feature and attributes. Acrylic varnish for instance is usually tinted with pigments making the finish colorful.
Varnish is commonly used for its resistance to UV rays, heat, and moisture. This is why varnish is seen on outdoor furniture and exterior walls.
However, varnish has one flaw. The sealant takes too long to cure and is difficult to clean and maintain. So is varnish better than polyurethane? The answer to this question depends on a few factors.
Polyurethane vs Varnish: Head to Head
Let’s go deeper into the make-up and features of both top coats to bring out the differences between them.
The Paint Make-Up
Varnish is an old finish. The paint make-up of varnish is a bit traditional when compared to polyurethane. Varnish packs a lot of compounds and natural matter in its paint formula. The formula includes tree resins, insect excretions (shellac), and fossil compounds.
Polyurethane however is a polymer that contains chemicals and strong binders. Polyurethane has more modern than traditional make-up. Polyurethane coatings contain polyols and esters. This makes polyurethane paint make-up more chemical-based while varnish has a more natural origin.
Related Read: Can You Varnish Over Polyurethane?
A key feature of any good sealant is flexibility. The sealant should be flexible enough to cope with temperature changes.
In terms of flexibility, varnish is more flexible than polyurethane. This is because varnish has a high level of plasticizers in the paint coating. Though polyurethane is also flexible, it’s not as elastic as varnish.
Polyurethane is more durable than varnish. This is because of the chemical nature of polyurethane. Also, the plastic-like texture of the polyurethane film makes it more resistant to chipping, dents, moisture damage.
Polyurethane when dry produces an ultra-thick plastic film that protects the wood finish. The most durable type of polyurethane is oil-based polyurethane.
Varnish is not as durable as polyurethane. The varnish contains a higher solids ratio compared to polyurethane. The solids in the varnish coating make it durable but most of these solids are gotten from natural matter. These solids aren’t as strong as the binders and chemicals in polyurethane.
Polyurethane dries faster than varnish. Water-based polyurethane can dry to touch in less than 1 hour. You can also subject the water-based polyurethane coating to regular use in about 24 – 48 hours meaning that the paint cures quickly too.
Varnish on the other hand will require several hours to dry and more hours to cure. Varnish can take up to 7 days (a week) to cure fully. The reason polyurethane dries faster is because the paint doesn’t have a high solid ratio. Most of the ingredients in polyurethane are liquids. The paint itself is plastic in liquid form.
Varnish however takes longer to dry and cure because of its high solid ratio. Since varnish has a higher solid to liquid ratio, the paint takes days to fully cure because it takes longer for the solids in the paint coating to dry.
Varnish is costlier than polyurethane. The cheapest polyurethane product is oil-based polyurethane. Then water-based polyurethane and varnish. The higher cost of varnish is due to the increased level of additives in the paint coating.
Varnish is more UV-resistant than polyurethane. This is because varnish is designed to cure when exposed to ultraviolet rays. When exposed to heat or UV rays, the varnish coating gets harder. So unlike most paints that will fade when exposed to UV rays, varnish benefits from the UV exposure.
The only type of polyurethane that is UV resistant is exterior or outdoor polyurethane. Ordinarily, polyurethane is not UV resistant and will fade if used on areas without UV protection.
With varnish, you have a broad range of choices. You can go for acrylic varnish which has a color tint, yacht varnish, and the likes. However, with polyurethane, your choice is limited to either water-based or oil-based polyurethane.
Clarity of Finish
Sealants like varnish and polyurethane are common for their clear top coat. These sealants when dry produce clear sheens on the material or paint. In terms of clarity, varnish is clearer than polyurethane. Also, varnish tends to remain clear and transparent for years. Polyurethane on the other hand, especially oil-based polyurethane tends to yellow over time.
Outdoor and Indoor Application
Polyurethane is designed primarily for indoor use. Polyurethane as explained earlier is thick and strong but not UV-resistant. As such, the finish is best suited for indoor application.
However, there is also polyurethane that can be used outdoors. Exterior polyurethane has additives included in the paint formula for UV-protection. But, exterior polyurethane is more expensive than regular polyurethane.
Varnish on the other hand is much more suited to outdoor application. This is due to the UV resistance and higher solid ratio of the sealant. Varnish is best used on outdoor furniture and exterior surfaces.
Paint Cleaning and Maintenance
Polyurethane is easier to clean and maintain than varnish for many reasons. For starters, polyurethane dries quickly so the paint coating is less likely to accumulate dust while drying. Varnish however takes several hours to cure.
The longer it takes for the paint to dry, the higher the possibility of dust nibs and grain settling in the finish. This debris will settle on the varnish and need cleaning up when the paint is dry.
Also, polyurethane repels dust and grease. Polyurethane as explained earlier is plastic. The plastic film doesn’t allow dust and grease to stick. So you can easily clean stains off of polyurethane.
Varnish however isn’t plastic. Varnish is a coat produced from natural matter and alkyd resins. As such, the varnish is more likely to allow dust nibs and stains to stick.
This means you’ll need more clean-up with varnish. Since varnish is also cleaned using solvents, the varnish coating might start to fade if exposed to consistent cleaning.
How easy is it to apply varnish and polyurethane? Varnish is much more difficult to apply than polyurethane. With polyurethane, you can apply it easily with a spray gun or paintbrush. Polyurethane also comes in spray cans so you just have to aim and spray even coats.
With varnish, however, you’ll find it more difficult to apply the paint. You’ll have to thin the varnish with a solvent before using it.
You have to wait longer before sanding or shaping varnish since the top coat takes forever to cure. You’ll also need multiple coats of varnish. This translates to a time-consuming paint application process.
Here is a chart that summarizes the differences between polyurethane and varnish.
|Paint Clarity||Very Good (up to 15 years)||Moderate if left unsealed|
|UV-resistance||Only exterior polyurethane is UV-resistant||Good|
|Cleaning and Maintenance||Easy||Difficult as you’ll need solvents|
Now that you know the differences between both paints. Which do you need?
Should I Buy Polyurethane or Varnish?
The answer to this question depends on your taste and needs. However, here are a few questions to answer before picking any of the top coats:
How Much Do You Have?
The biggest determining factor behind which top coat to use is the price tag. Varnish is more expensive than polyurethane. So, if you want a pocket-friendly alternative, go for polyurethane. The cheapest option is oil-based polyurethane as water-based poly is also expensive.
Indoor or Outdoor Use?
You should also consider the surface to be painted or coated. If it’s outdoor furniture, the varnish is better. For indoor furniture like desks, polyurethane is better.
Slow-dry or Quick-dry Paint?
If you need a sealant that will dry on time, polyurethane is better as it dries and cures quicker. Varnish will take up to 3 days to get dry and about a week to cure enough for regular use.
Do You Need UV-protection?
If you would be painting or coating a surface that will be exposed to UV rays, it’s better to go for varnish. That’s because varnish has additives that make the paint cure harder under UV reflection.
Polyurethane is not suited for UV protection. It’s more suited for indoor surfaces that will be shielded from UV lights. However, you can also go for exterior polyurethane.
Do You Want Easy Maintenance?
Polyurethane is easier to clean and maintain than varnish.
Do You Need Durability?
Polyurethane is more durable than varnish and as such is more suited to high traffic areas in the home. Varnish though UV-resistant is not as durable as polyurethane.
Polyurethane & Varnish Uses
Here is a chart that indicates the ideal uses of polyurethane and varnish based on the strengths and weaknesses of the finish.
|Indoor or Outdoor Use?||Indoor||Outdoor|
|Heat Resistance||Good||Poor or Moderate depending on the type of varnish|
|Cleaning and Maintenance Level||Low||Moderate|
|Finish||Clear plastic||Clear Top coat|
|Strength and durability||Good||Good|
Overall, polyurethane and varnish are both great paint types. I know how challenging it is to pick one of the two but I hope this post has made that decision easier.