There are numerous epoxy suppliers on the market and the common message from installers is that "all epoxies are the same, they just have a different labels on them." This is not always true. The base resin may be the same for all companies, but each manufacturer will usually have their own blend of additives that make the end product a little different. These additives may include;
- Anti-foaming agents
- UV stabilizers
- Solvents to extend working time/pot life
- Thinning agents to lower viscocity
From a chemistry standpoint, two part epoxies are convertible coatings meaning the two parts (Part A - Resin and Part B - Hardener) chemically react with each other during the curing process. This chemical cross-link produces a chemical change and forms the hard film. On a very basic level, cured epoxies are just a layer of hard plastic.
There are four basic classifications of epoxy:
1) Bisphenol-A (Bis-A) - This is probably the most common for general purpose epoxy resins. Most floor coating epoxies are Bis-A.
2) Bisphenol-F (Bis-F) - This is more tightly cross-linked epoxy with better chemical resistant properties. Oftened sold as a "chemical resistant" epoxy, these tend to be more expensive.
3) Novolac Epoxy - These are the "bread & butter" coatings for secondary and even primary containment applications. The cross-link of these epoxies is three dimensions and therefore much more dense giving them superior chemical resistance to strong acids (98% sulfuric acid) and caustics (50% Sodium Hydroxide).
4) Polyamide Epoxy - These two part epoxies are often "solvent based" epoxies that often require a 20-30 minute induction or "sweat-in" time. They often have long working time (2-4 hours) with fast recoat and cure times (1-2 hours). However, they are limited to just 6-8 mils WFT per coat because of the solvent. Polyamide epoxies work very well in wet or immersion environments.