UV Exposure and Epoxies
Despite several excellent properties including low shrinkage, good chemical resistance, curable at low temperatures, and the absence of byproducts or volatiles, epoxy resins are susceptible to ultra violet (UV) damage and their durability is reduced substantially when exposed to outdoor environments. All epoxies will break down in direct sunlight because their chemical structure becomes unstable when exposed to UV light. Because of this, epoxies are better suited for indoor coatings in facilities such as factories, warehouses, commercial kitchens, offices, and homes. Even indoors epoxies can have film issues and thus yellow due to light coming from windows; however this is not a problem if the windows are laminated with a UV blocker. Epoxy floors can also be damaged by UV light from fluorescent tubes. Similarly, IR heat lamps in bathrooms can cause problems over time. Although UV exposure leads to film issues, there is not much of a risk of chalking or cracking on indoor floors as they do not need to contend with rain or extreme temperature fluctuations.
Something important to keep in mind is that all floor coatings will eventually degrade and discolor; the difference is epoxies are unusually susceptible to UV exposure. Some resinous flooring products 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.
There are epoxy formulations that can delay the damaging effects of UV light. One approach is using a combination of UV absorber with HLAS (Hindered Amine Light Stabilizer) however, eventually in outdoor applications the UV stabilizers will have maxed out there ability to absorb or will be washed away and no longer be effective. Nevertheless, the UV stabilizer approach is sufficient to enhance color stability of epoxy in indoor applications, especially when there is minimal lighting from windows. How long these UV stabilizers are effective is difficult to say; epoxies can typically be made to be UV resistant for a few months or even a year, but never for the lifespan of the floor.
Additionally, there are UV blocking zinc nano additives available but these additives prevent the epoxy from curing properly, which causes it to have inadequate mechanical strength. Other non-zinc-oxide nano types are colored and cannot be used with clear epoxy coatings. The effectiveness of these nano additives is not proven in all formulations and even with the additives it will still not make the epoxy as UV stable as aliphatic polyurethanes, polyaspartics, or acrylics.
One misconception a lot of resinous installers have is that a clear coat of aliphatic urethane will protect the floor from discoloring. While it is true that aliphatic urethanes will not discolor, it will not protect the epoxy base coat because the UV light will actually penetrate the aliphatic topcoat. However, colored aliphatic urethanes can protect the floor from UV damage. To see an excellent case study on a project using this strategy check out this link: https://www.highperformancesystems.com/warehouse-sealing-nj.
With all of this in mind the best way to have a long lasting epoxy floor is to get a industrial flooring expert with substantial experience to evaluate the condition of your epoxy floor. To learn more about epoxies and resinous flooring generally check out my previous blog posts on “How To Prevent A Coating Failure,” “What Types of Substrates Can Epoxy Be Applied Over,” and “Epoxy vs. Urethane Floor Coatings.”