Epoxy resins carry strained, three-membered epoxide rings that open and crosslink with amine hardeners. The result is unmatched adhesion and chemical resistance for primers, floors, linings and composites.
Most coating epoxies are glycidyl ethers: molecules made by reacting a bisphenol or phenolic resin with epichlorohydrin so that each end carries an epoxide ring. The standard liquid resin is based on bisphenol A; bisphenol F versions are thinner and more solvent-resistant; novolac epoxies carry more rings per molecule for maximum chemical and heat resistance.
When mixed with an amine hardener, each active hydrogen opens one ring and the network grows in three dimensions. The aromatic backbone and dense crosslinks give epoxies their hallmark adhesion to steel and concrete, hardness, and resistance to water, fuels and many chemicals.
That same aromatic structure absorbs UV, so standard epoxies chalk and amber outdoors. They usually serve as primers and intermediate coats, topcoated with polyurethane or polyaspartic where appearance matters. Reactive diluents thin resins for self-leveling floors, at some cost to chemical resistance.
The base resins and modifiers behind epoxy primers, floors and linings.
Used forGeneral-purpose floors, primers, tank linings and composites.
The workhorse standard liquid epoxy. Excellent adhesion, but chalks and ambers in sunlight.
Full profileUsed forReference compound and high-purity crystalline grades.
Commercial liquid resins are mostly this molecule plus small oligomers.
Full profileUsed forLow-viscosity, crystallization-resistant floors and linings.
Lower viscosity and better solvent resistance than standard BPA resin.
Full profileUsed forTank linings, secondary containment, acid and solvent resistance.
Higher functionality means denser crosslinks and better heat and chemical resistance.
Full profileUsed forWeatherable epoxy topcoats and UV-resistant clear systems.
Saturated rings resist UV chalking far better than standard BPA resins.
Full profileUsed forCuts viscosity of floor and self-leveling epoxies.
Reduces viscosity but also crosslink density. Use sparingly where chemical resistance matters.
Full profileUsed forHighly efficient viscosity reducer for epoxy resins.
More volatile and a skin sensitizer; many formulators prefer heavier diluents.
Full profileUsed forReacted with bisphenols to manufacture epoxy resins.
Not used in coatings directly. IARC lists it as probably carcinogenic (Group 2A); residuals in resins are kept very low.
Full profileThe epoxide ring is a strained triangle of two carbons and one oxygen. An amine nitrogen attacks the less hindered carbon, the ring springs open and a hydroxyl group is left behind. A primary amine has two hydrogens, so it can open two rings, and the hydroxyls formed along the way help adhesion.
Getting the ratio right matters more than with most chemistries. Using EEW for the resin and AHEW for the hardener, parts of hardener per 100 parts resin = AHEW × 100 ÷ EEW. Off-ratio mixes leave unreacted material that softens the film and reduces chemical resistance.
Epoxy cure depends strongly on temperature. Below roughly 10 °C (50 °F) many systems slow dramatically, and humid air promotes amine blush on the surface.
R′–NH₂Amine hardenerR–CH(OH)–CH₂–NH–R′β-Hydroxy aminephr hardener = AHEW × 100 ÷ EEW
Generalized ratings (5 = best). Hardener choice and formulation shift these considerably.
| Resin | Typical EEW | Viscosity | Chemical resistance | UV resistance | Typical use |
|---|---|---|---|---|---|
| Bisphenol A | 182–192 | Medium | Floors, primers, linings | ||
| Bisphenol F | 165–175 | Low | Self-leveling floors, linings | ||
| Epoxy novolac | 172–181 | High | Tank linings, containment | ||
| Hydrogenated BPA | 210–240 | Low | Weatherable topcoats | ||
| With reactive diluent | Varies | Very low | Thin, flowable floor systems |
Uncured epoxy resins and amine hardeners are among the most common causes of occupational allergic contact dermatitis. Sensitization builds with repeated skin contact.
Always follow the product’s Safety Data Sheet, your employer’s safety program and local regulations. This page is general reference information, not a substitute for them.
Epoxide equivalent weight: the grams of resin that contain one epoxide group. Standard liquid bisphenol A resin is about 182–192 g/eq. It is used with the hardener’s AHEW to calculate the mix ratio.
The aromatic bisphenol structure absorbs UV light, which breaks down the surface. Outdoor epoxies are usually topcoated with a UV-stable polyurethane or polyaspartic.
BPF resins have lower viscosity, better solvent resistance and less tendency to crystallize in cold storage. BPA resins are the economical, general-purpose standard. Many floor systems blend both.
A low-viscosity glycidyl ether, such as C12–C14 alkyl glycidyl ether, that thins the resin and reacts into the network. It improves flow but lowers crosslink density and chemical resistance.