Does UV Resistant Epoxy Exist?

Epoxy resin is a unique thermoset plastic which is made by liquid materials reacting with each other and irreversibly forming an inert highly crosslinked solid polymer (plastic) structure.

Epoxy is used in a wide variety of applications for coatings and adhesives, including on concrete, wood, FR plastic, PVC, glass and metals. It has outstanding toughness, hardness, mechanical strengths and durability, which makes it 4 times stronger than concrete.

However, some drawbacks of epoxy are its poor scratch and UV resistance. It tends to discolor (amber) rapidly upon exposure to UV and even with indoor applications, epoxy still ambers over time; the degree at which it will discolor depends on the specific formulations and ingredients used.

It can range from severe discolouration (browning) to slight ambering, all dependent on the product. It is important to mention that not all epoxy coatings in the market are the same, some are better than others.

There Is No Such Thing as a UV Resistant Epoxy

UV Exposure-Related Damages

In the coating industry, some polymers, such as polymethyl methacrylate (MMA), polyaspartic acids, and aliphatic polyurethane, are photochemically stable between the 300 and 400 nm where the UV lights are, because they do not absorb them. Only light that is absorbed is capable of initiating photochemical processes and irreversible damage to the coatings.

When the epoxy coating is exposed to UV light, either directly or indirectly, it causes a noticeable and permanent damage as a result of photo degradation, including loss of gloss, ambering (i.e. a yellow discoloration), and for the coloured one chalking and breakdown of the coating may also result.

UV rays from the sun turn epoxy yellow and an epoxy floor exposed to sunlight will always eventually amber. The ingredient selection in the formula to produce somewhat a colour stable epoxy is very crucial. Many of standard plasticizers, modifiers and amine curatives are not suitable for the purpose and tend to discolor readily.

Does UV-Resistance Epoxy Exist?

There has been great advancement in stabilizing epoxy coating in the recent years. One approach is using a combination of UV absorber with HLAS (Hindered Amine Light Stabilizer). This combination is very effective in delaying the damaging effect of UV on epoxy coatings, but unfortunately it is not permanent.

Eventually in outdoor applications the UV stabilizers would be full or washed away and no longer effective. Nevertheless, the UV stabilizer approach is sufficient to enhance colour stability of epoxy in indoor applications, especially when the sun’s lighting is strong from large windows.

How long these UV stabilizers are effective is hard to tell, it could take from a few months to a year to amber. Hence, epoxy can be made to be UV resistant for a few months or even year, but never for long term.

There are also UV blocking additives, but these zinc nano additives interfere in the epoxy-amine reaction producing incomplete cure and inadequate mechanical strength. Other non-zinc-oxide nano types are colored and cannot be used with clear epoxy coating.

The efficiency of these nano additives is not proven in all formulations, and some care has to be taken to ensure its workability in a given formula. Even with that, the UV blocker will not make epoxy as colour stable as aliphatic polyurethanes, polyaspartic acid, or acrylics.

The greatest misconception in the market is that a clear coat of aliphatic urethane (or polyaspartic acid) will protect your floor from turning yellow from the sun. This is a myth. It is true that the aliphatic polyurethane will not discolour (turning yellow or amber), but your floor beneath it is still susceptible to UV and will amber because the sun goes through the clear urethane, and yellows the epoxy floor.

Only coloured (pigmented) aliphatic polyurethane or polyaspartic acid can protect the floor beneath it from UV.

Take a look at our product review.