What Type of Epoxy Are You Using and Why?
Posted by Steven Wadsworth on
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.
You are spot on with the assessment that many installers feel all epoxies are the same with different labels. To be honest, I cannot blame them from feeling that way. With the constant consolidation of manufacturers and the big getting bigger to leverage buying power of base resin like Bis A and F they start undercutting to win work and take a “me too” stance with the material. The salespeople turn over frequently and are not trained to sell the value or difference in what is inside the can and fundamental differences between resin and cure. In short, applicators are in general being misled in to thinking it is all the same.
If I may, to add to your notes on bullet point number 4. Also consider there are additional resin/cure combinations available to broaden the spectrum of offering to the end user. Without getting to crazy here, another to consider is polyamine cured epoxy. The amine cure typically provides a more durability an chemical resistance. Epoxy Phenolics are also available for high temp applications that some Novolac’s might struggle to reach.