Polyurethane vs. Epoxy (What’s The Difference?)

You can use polyurethane or epoxy for your floor or concrete. But, what’s the difference between epoxy and polyurethane?

Epoxy is more durable and harder than polyurethane. As a result, epoxy is used for high-traffic surfaces such as factories or warehouses. In comparison, polyurethane is used for medium-traffic surfaces such as house floors.

Polyurethane is softer and more flexible than epoxy, but epoxy has better adhesive qualities, especially for concrete surfaces. Epoxy can cure even in humid conditions, while polyurethane is affected by humid conditions. 

There are more differences between these two coatings that we discuss down below. 

Epoxy Paint

What is Epoxy Paint?

Epoxy paint is a strong paint that comes in 2 parts; resin and hardener. You must mix both epoxy parts in a ratio of 1:1 before using. The mixture of both parts creates a strong layer (film) known as epoxy.

There are also 1 part epoxy paints that you don’t need to mix. But, 1 part epoxy isn’t as durable as 2 part epoxy. Also, there are different variations of epoxy. For example, you can get flexible epoxy, floor epoxy, fast-settings epoxy, etc.

Epoxy paint has impressive bonding qualities, especially for concrete and masonry surfaces. The increased bonding qualities are due to the chemical reaction when two epoxy parts are mixed.

Also, epoxy has a thick flow, meaning it will take the paint longer to dry and cure. For instance, 2-part epoxy flooring can take up to 7 days to cure. However, epoxy isn’t affected by humid conditions and will cure regardless of the humid levels.

However, epoxy can’t cope well with temperature changes because the finish is rigid. So, it’s best to use epoxy on floors and concretes that aren’t exposed to temperature changes. Also, epoxy tends to yellow over time if exposed to UV rays. 

Polyurethane

What is Polyurethane?

Polyurethane is a plastic-like sealant used as a topcoat (or sealant) to protect the material (or finish) underneath.

When dry, polyurethane forms a glossy layer over the surface. This glossy layer of polyurethane is water-resistant, chip-resistant, and sometimes UV-resistant. This makes polyurethane durable.

Since polyurethane contains plasticizers in its formula, the finish is flexible. As a result, polyurethane can cope with hot and cold temperatures.

Polyurethane has a quick-drying time. For example, water-based polyurethane cures within 24 hours, while oil-based polyurethane cures within 48 hours. You can also get different finishes for polyurethane, such as medium-gloss or high-gloss.

Epoxy vs Polyurethane

So which of these finishes is better? Let’s go deeper into the characteristics of both finishes to bring out their differences, strengths, and weaknesses.

Paint Make-Up

Paint Make-Up

Both sealants have different make-up and formation.

Polyurethane is obtained from the reaction between polyols and diisocyanates or isocyanate compounds. On the other hand, epoxy is obtained from the reaction between a resin and hardener, which you must mix manually.

The difference in paint make-up gives both finishes some different features. For instance, epoxy is known to be thicker than polyurethane because you have to mix two equal coatings (or parts) to make epoxy.

Flexibility

Paint flexibility refers to the elasticity of the paint.

Polyurethane is more flexible than epoxy. That’s because polyurethane has plasticizers in the paint coating. The plastic nature of the polyurethane film makes it stretch and contract based on temperature changes. This gives polyurethane improved flexibility.

On the other hand, epoxy paints are more rigid, hard, and brittle. So, the epoxy floor will crack if exposed to temperature changes.

Paint Drying

Polyurethane dries faster than epoxy. For example, water-based polyurethane dries enough for a re-coat within 8 hours, while oil-based polyurethane dries enough for a re-coat within 24 hours. On the other hand, epoxy must cure for 7 days before you can use or clean it. 

However, epoxy isn’t affected by humid conditions, while polyurethane is. So, if the humidity levels are too high, polyurethane will take longer to dry than epoxy. 

Paint Adhesion

Epoxy has better bonding qualities than polyurethane, especially for concrete surfaces. That’s because epoxy is made from two compounds that improve paint adhesion; resin and hardener. When mixed, these two compounds produce an epoxy paint that will bind to any material. 

Polyurethane also has good adhesive qualities but doesn’t stick as well as epoxy. That’s because polyurethane doesn’t penetrate the surface as much as other sealants.

However, for both sealants to stick, you must prep the surface before applying them. 

Durability

Both sealants are durable and strong enough. For instance, polyurethane is more flexible and can adapt to temperature changes. So, if used outdoors, polyurethane is more durable than epoxy.

However, for basement floors or indoor concrete, epoxy is more durable than polyurethane. That’s because epoxy forms a thick layer that is strong, hard, and durable. Since indoor surfaces aren’t exposed to temperature changes, the epoxy finish will last years before it starts to chip off. 

Paint Hardness

Epoxy paint is harder than polyurethane. When dry, 2-part epoxy forms a hard sheen layer that is hard, durable, and strong. The hardness of epoxy makes it ideal for surfaces that will see heavy usage.

On the other hand, polyurethane has a thick plastic-like finish that is softer than the epoxy finish. 

Paint Application

To apply polyurethane, you can use a spray gun, paint roller, paintbrush, or a rag (wiping it on the surface). However, epoxy paint can only be applied with a roller.

Paint Variety

Polyurethane offers more shades, types, and finishes than epoxy. Polyurethane has two types; oil and water-based. But, you can choose different sheen finishes; satin, medium-gloss, or high-gloss polyurethane finish. 

On the other hand, epoxy has a limited range of choices. All you get with epoxy is a strong and hard coating since epoxy isn’t designed for decor or aesthetics.

Indoor or Outdoor Use

For outdoor, polyurethane is better than epoxy. That’s because polyurethane is flexible and can cope with temperature changes. 

For indoors, epoxy is better than polyurethane. That’s because epoxy forms a hard, rigid coating that can withstand heavy weights and high foot traffic. That’s why epoxy is used in warehouses or factories.

Do You Need Polyurethane or Epoxy?

Before you make that decision, ask yourself a few questions.

  1. Budget – Get the paint you can afford. Two-part epoxy is more expensive than polyurethane. 
  2. Indoor or Outdoors – For indoor floors, use epoxy. For outdoor floors, use polyurethane.
  3. Surface You Will Paint – Use polyurethane for decorative, kitchen, or dining surfaces. Polyurethane offers a more decorative finish. For concrete floors in your garage, use epoxy.
  4. High-traffic Areas – For surfaces exposed to heavy weights, such as cars, use epoxy. Epoxy can withstand more weight than polyurethane. However, for patios or walkways, use polyurethane because it’s more flexible.

Related Read: Can You Put Epoxy Floor Over Paint?

Using Polyurethane Over Epoxy

You can use a polyurethane top coat over epoxy. You will get a hard, strong, durable, and flexible finish. Since epoxy has better paint adhesion, you can apply it first and then apply the polyurethane.

Epoxy is stronger than polyurethane and can be a great undercoat option. When epoxy cures, you can seal it with 1-2 coats of polyurethane. The polyurethane will make the epoxy resistant to water, moisture, scratches, and UV lights.

So, if you apply polyurethane over epoxy, you will get a durable finish that is strong enough to withstand heavy weights. But, also flexible enough to cope with temperature changes. So, it’s the best of the two worlds.

Tip: The best polyurethane to use over epoxy is oil-based polyurethane.

Final Words

The main difference between polyurethane and epoxy is the flexibility of polyurethane and the rigidity of epoxy. Polyurethane is more flexible and can cope with temperature changes; this makes it ideal for outdoor surfaces. While epoxy has a harder and more durable finish, it is ideal for indoor surfaces such as basement floors.

However, you can apply polyurethane over an epoxy finish to get the features of both sealants. 

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