PennCoat Epoxy Coatings – Aliphatic Urethanes

PennCoat Epoxy Flooring - Aliphatic Urethane Top Coat

Aliphatic Urethane

You can choose among several classes of topcoats when you need to protect a surface such as a floor. Two popular types of topcoats are those made from epoxy and those made from aliphatic urethanes. The epoxy topcoat will give good results in a range of applications, but aliphatic urethanes display superior performance, including resistance to abrasion, chemicals and UV light. They are environmentally friendly and emit little odor. These characteristics stem from the primary ingredient in aliphatic urethane: hexamethylene diisocyanate (HDI) and its homopolymer.

Hexamethylene Diisocyanate

The structure of HDI is a six-carbon hexane chain with an isocyanate group (N=C=O) at each end. The two isocyanate groups are symmetrical and equally active. The formula for HDI is C8H12N2O2, with a molecular weight of 168.19 grams per mole. HDI, which is aliphatic, or straight-chained, is superior to urethanes made with aromatic, or ring-like, isocyanates and to most epoxies because it doesn’t discolor when exposed to light. The homopolymer of HDI consists of repeating units of the HDI monomer. Polymerization gives aliphatic urethanes their great durability and hardness.


Epoxy is a mixture of resins and hardeners that offer good protection to surfaces when used as a coating or grout. It also forms an ultra-strong adhesive. An epoxy grout coat is commonly used for seamless flooring systems. Typical products contain transparent two-part thermosetting epoxy with 100 percent solids, consisting of one part hardener and two parts resin. Some epoxy floor coverings have been engineered to provide good UV resistance, low odor and excellent clarity.

Urethane vs Epoxy

Coatings such as epoxy topcoat and aliphatic urethane provide long-lasting protection to areas such as garage floors and food and pharmaceutical production floors. However, the structure of the urethane gives it a three-fold advantage in wear-resistance. While an epoxy coating is harder, aliphatic urethane is more scratch resistant. It also can tolerate greater temperature swings and is a much better protectant against humidity. You can get a higher gloss with aliphatic urethane. The urethane typically has tensile strength of 7,000 psi compared to epoxy’s 2,100. The coefficients of friction are close: 0.6 vs 0.7, respectively. Both products have a pot life of 45 minutes. Aliphatic urethane is usually available in clear satin or high gloss and in multiple colors, while epoxies are often clear-only. PennCoat uses both products for industrial and commercial floor-coating applications.