Aliphatic urethane is the type of urethane that is most commonly used as the topcoat for epoxy floor systems. There are two other types of urethane: aromatic and waterborne. Aliphatic, however, is a better choice for concrete sealing because it will not turn to the color amber when exposed to UV light (from the sun), like aromatic urethanes will. While waterborne urethanes also will not amber, they are not as strong as aliphatic, which offers excellent abrasion and chemical resistance, as well as strong color and gloss retention. Aliphatic urethanes are most well known for offering UV stability and protection from the suns rays, and are highly resistant to severe weather, due to their chemical composition. Their bonds are extremely strong, and they typically last for a long time.
Urethanes in general are used as a topcoat for epoxy floor systems, meaning they rarely are used as a standalone product. Epoxy floor systems are a series of products that are used on rougher floors that feature heavy traffic, such as in airports, commercial retail stores, or industrial settings. They typically consist of a primary coat of a basic epoxy, designed to bond to the substrate on the surface, much like an acrylic surface sealer. Because the particles of material are larger than with penetrating sealers, the epoxy will not delve within the concrete, instead pooling on the surface to be spread out evenly during application.
After this epoxy base coat, you are ready to add the urethane topcoat. An aliphatic urethane, while slightly more expensive than aromatic, is really the only choice of topcoat. Aromatic will yellow at the slightest sunlight and will also not last nearly as long, as it is not as strong of a bond.
Ghostshield offers an aliphatic urethane product Urethane 645. The Urethane 645 is a two-component urethane and is a great choices as a topcoat for your epoxy-sealed floors that offer an excellent level of protection.