To seal paint or surfaces, you can use polyurethane or varnish. But, what’s the difference between these two sealants?
Varnish is an old finish gotten from combining resins, paint chemicals, oils, and solvents. On the other hand, polyurethane doesn’t have as many chemicals and its main ingredients are polyols and isocyanates or diisocyanates.
There different types of varnish, but there are only two types of polyurethane; oil and water-based. In addition, some types of varnish come with a colored finish, while polyurethane has a clear coat finish (no paint pigments).
Polyurethane is a topcoat that protects surfaces from moisture, water, scratches, and other damage. When dry, it forms a glossy clear coat that protects the surface underneath.
There are two types of polyurethane; oil-based and water-based poly. Oil-based polyurethane is thicker and takes longer to dry but offers better protection than water-based polyurethane. There’s also exterior polyurethane used for outdoor surfaces.
You can apply it using a sprayer, brush, roller, or by wiping it on surfaces.
Varnish is one of the first wood sealant products, which is why most wood sealants are called “sealants”. Since varnish is old, the sealant is made of strong resins and chemical and natural additives.
Varnish is a sealant that protects surfaces from water, moisture, and other damage. There are different types of varnishes. For instance, acrylic varnish is a colorful and durable finish created by adding acrylic paint pigments to the varnish coating.
However, this sealant takes too long to dry fully (cure) and is difficult to clean and maintain.
Varnish vs Polyurethane
Let’s check the make-up and features of both top coats to bring out their differences.
The Paint Make-Up
Varnish is an old finish, and its make-up is traditional compared to polyurethane. It has a lot of compounds and natural matter in its formula. Its formula includes tree resins, shellac, and compounds.
On the other hand, polyurethane is a polymer that contains strong binders and polyols, and esters. This means it has a more modern than traditional make-up.
Related Read: Can You Varnish Over Polyurethane?
Varnish is more flexible than polyurethane it has a high level of plasticizers in the formula. However, polyurethane is also flexible, but not as elastic as varnish.
Polyurethane is more durable than normal varnish, but spar varnish is more durable than polyurethane. The plastic-like texture of polyurethane makes the coating more resistant to chipping, dents, or moisture damage. In addition, exterior polyurethane forms an ultra-thick plastic film that protects outdoor surfaces from weather elements.
On the other hand, the varnish is also durable. Varnish has a higher solids ratio than polyurethane, but the solids in varnish are gotten from natural matter. So, the solids aren’t as strong as the binders in polyurethane.
Polyurethane dries faster than varnish. On average, water-based polyurethane dries fully (cures) within 24 hours, while varnish takes 7 days (a week) to dry fully.
Polyurethane dries faster because it doesn’t have a high solid ratio. Most of the ingredients are liquids that evaporate fast. Varnish takes longer to dry because the high solid ratios take longer to evaporate from the coating.
Varnish costs more than polyurethane. The cheapest polyurethane is oil-based poly, then water-based poly and exterior. Varnish costs more because of the increased level of additives in the coating.
Varnish is more UV-resistant than polyurethane because it’s designed to dry fully when exposed to UV rays. So, the more the coating is exposed to UV rays, the stronger and harder it gets.
On the other hand, only exterior polyurethane is UV-resistant. Water-based and oil-based poly aren’t and will fade if exposed to UV rays.
Varnish comes in different types. For instance, acrylic varnish has a colored finish (gotten from acrylic pigments) and a strong and durable finish (gotten from varnish).
On the other hand, polyurethane has only two types; oil-based and water-based.
Clarity of Finish
Both varnish and polyurethane have a clear finish that doesn’t change the color shade of a surface. However, varnish has a clearer finish than polyurethane. Its finish remains clear and transparent for years, while polyurethane tends to yellow over time.
Outdoor and Indoor Application
Water-based and oil-based polyurethane are designed for indoor surfaces and exterior polyurethane is designed for outdoor surfaces. You can also use oil-based poly outdoors, but the finish won’t last as long as exterior poly.
On the other hand, the varnish is designed for outdoor surfaces.
Paint Cleaning and Maintenance
Polyurethane is easier to clean and maintain than varnish. That’s because it dries faster, so there’s less time for the dust to settle on the finish while drying. Varnish takes longer to dry, so more dust settles over the finish.
Also, polyurethane repels dust and grease because of its plastic-like finish. The plastic film doesn’t allow dust or grease to stick. So, cleaning it is easier.
On the other hand, varnish doesn’t repel dust, so you must do more clean-up. Also, to clean it, you must use solvents that can fade the coating if exposed to constant cleaning.
Polyurethane is easier to apply than varnish. You can apply it using a spray gun, paintbrush, roller, or rag. Also, polyurethane comes in spray cans that don’t need extra prepping.
On the other hand, you must thin varnish before applying it. Since it takes longer to dry, you must wait longer before sanding between coats. Also, you need multiple coats, meaning the application takes longer to complete.
If you want the best of two worlds, use polyurethane varnish. Polyurethane varnish combines polyurethane and varnish to create a super durable finish. This sealant is used to protect and seal indoor and outdoor surfaces.
The finish is durable, lasts longer, and offers a glossy sheen.
|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?
Do You Need Varnish or Polyurethane?
Before choosing one of the sealants, consider these things:
- Budget – Varnish costs more than polyurethane. However, acrylic varnish comes colored, so you don’t have to tint it. But, if you want a cheaper option, use oil-based polyurethane.
- Indoor or Outdoor – For indoor surfaces, use water-based polyurethane. For outdoor surfaces, use spar varnish or exterior polyurethane.
- Time – Varnish takes longer to dry, meaning its application takes longer. On the other hand, polyurethane dries fast and needs fewer coats, so its application takes less time. So, if you need to seal a surface faster, use polyurethane.
- Maintenance – Polyurethane is easier to clean and maintain than varnish.
- Durability – If you want a super durable finish, use spar varnish. If you want normal protection, use oil-based polyurethane.
Polyurethane and varnish are two durable sealants. However, these sealants have a different formulas, meaning their finish and features are different.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,