You have the epoxy resin picked. Now the hardener column on the data sheet has a dozen options, the mix ratios range from 11 to 50 parts, and the wrong pick gives you a coating that blushes in the cold, a casting that cracks on demold, or a laminate that softens at the service temperature you promised. The curing agent, not the resin, sets most of what the cured part actually does: how fast it gels, how long you have to apply it, how hot it has to cure, what color it ends up, how rigid or tough it is, and whether it blushes. This guide compares the amine hardener classes on those axes and shows you how to calculate the mix ratio by weight so you stop eyeballing it.
The short version: An epoxy curing agent (hardener) reacts with the resin’s epoxide rings to build the crosslinked network, and the class you choose sets reactivity, pot life, cure temperature, color, glass transition temperature (Tg), flexibility, and blush tendency. Unmodified aliphatic amines (DETA, TETA, TEPA) are fast, cheap, and rigid but blush-prone. Cycloaliphatic (IPDA) and araliphatic (MXDA) amines give better color and chemical resistance. Polyamides and amidoamines trade speed for long pot life, flexibility, and damp-surface tolerance. Mannich bases / phenalkamines cure fast in cold, wet conditions. Polyetheramines (comparable to Jeffamine grades) add toughness and flexibility at lower Tg. Aromatic amines reach the highest Tg but cure slowly with heat, yellow, and turn brittle. You set the mix ratio from the hardener’s amine hydrogen equivalent weight (AHEW) and the resin’s epoxy equivalent weight (EEW): phr = (AHEW / EEW) x 100, by weight, because each epoxide group needs one amine N-H.
What a curing agent actually does
Amine-cured epoxy hardens because the nitrogen-hydrogen (N-H) groups on the amine react with the epoxide rings on the resin. Each active amine hydrogen opens one epoxide ring and forms a covalent bond, so a hardener with several N-H groups ties multiple resin chains together into a three-dimensional network. The density and rigidity of that network is what you feel as hardness, heat resistance, and chemical resistance.
This is why the hardener is the bigger lever, not the resin. Standard liquid bisphenol-A resin (DGEBA) is the same molecule across most suppliers, yet cure it with a small aliphatic amine and you get a hard, rigid part; cure the identical resin with a polyetheramine and you get a tough, flexible one. Pick the hardener to your performance target first.
The amine hardener classes, compared
The table below is the selection map. Read it top to bottom roughly fastest-and-cheapest to slowest-and-highest-performance. No single class wins every column; the right answer depends on your cure conditions and your service requirements.
| Hardener class | Cure speed | Pot life | Typical cure temp | Color / yellowing | Tg / heat resistance | Flexibility / toughness | Blush tendency | Typical use |
|---|---|---|---|---|---|---|---|---|
| Aliphatic polyamines (DETA, TETA, TEPA, AEEA) | Fast | Short | Ambient | Moderate, ambers | Moderate | Rigid, can be brittle | High | Low-cost ambient coatings, adhesives, casting (warm/dry) |
| Cycloaliphatic amine (IPDA) | Moderate (slow without accelerator) | Medium-long | Ambient to warm | Low, good gloss and UV hold | Moderate-high | Rigid | Lower | High-spec clears, flooring, gelcoats, composites |
| Araliphatic amine (MXDA) | Fast-moderate | Short-medium | Ambient | Low | High for an ambient amine | Rigid | Moderate | Fast chemical-resistant coatings, adhesives |
| Polyamides | Slow | Long (often 4-8 h) | Ambient (sluggish when cold) | Ambers | Lower | Flexible, tough | Low | Maintenance and marine coatings, flexible adhesives |
| Amidoamines | Slow-moderate | Long (up to ~30 h grades) | Ambient, tolerates damp | Ambers | Lower-moderate | Flexible | Low | Concrete primers, low-odor humid-cure coatings |
| Mannich bases / phenalkamines | Very fast, cures cold and damp | Short | Ambient and low temp (down to near 0 C) | Dark amber | Moderate | Moderate-flexible | Very low | Marine, tank linings, cold/wet jobsite flooring |
| Polyetheramines (comparable to Jeffamine D/T grades) | Slow | Long | Ambient to warm | Low | Lower (raise with co-cure or heat) | High, tough, ductile | Low | Toughening/flex blends, flooring, composites |
| Aromatic amines (e.g., MDA, DDS) | Very slow | Very long | Heat cure (often >120-150 C) | High, yellows | Highest (Tg ~150-210 C) | Brittle | Low | High-temp composites, electrical laminates |
| Anhydrides | Slow, heat cure + accelerator | Very long | Heat cure | Low | High | Rigid | n/a (not an amine) | Electrical castings, filament winding, potting |
| Imidazoles (catalytic / latent) | Tunable; latent at room temp, fast with heat | Long (latent) | Heat cure / one-component | Low-moderate | High | Rigid | n/a | One-component adhesives, electronics, powder coatings |
Aliphatic amines: fast, cheap, rigid, blush-prone
The workhorses. Diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) are small, low-viscosity, highly reactive molecules that cure at room temperature, build a tightly crosslinked network, and cost the least per pound. They have low color impact in the can and give excellent solvent and chemical resistance. The trade-offs are a short pot life, a brisk exotherm in mass, a rigid and sometimes brittle film, and the highest blush tendency of any class, especially in cold or humid air. Aminoethylethanolamine (AEEA), an aliphatic amino-alcohol in the same family, carries a hydroxyl group that speeds cure and improves adhesion, and is often blended in for that reason. Choose aliphatics when you are working warm, dry, and ventilated. (For why these blush and how to control it, see our amine blush guide.)
Cycloaliphatic and araliphatic amines: color, gloss, and weathering
When color hold and surface appearance matter, move to a ring-containing amine. Isophorone diamine (IPDA) is a cycloaliphatic amine prized for low yellowing, high gloss, good UV and weathering resistance, and a moderate Tg; it is a standard for high-spec clear coatings, flooring, gelcoats, and composites. It cures more slowly than an aliphatic amine at ambient and is often paired with an accelerator. m-Xylylenediamine (MXDA) is technically araliphatic (an aromatic ring with aliphatic amine groups); it cures faster than IPDA, reaches a relatively high Tg, and delivers strong chemical and water resistance, which makes it common in fast protective coatings and adhesives. To cut blush and improve handling on a cycloaliphatic, a modified grade such as the cyanoethylated IPDA (Michael adduct) pre-reacts some of the amine to raise its molecular weight and tie up free N-H.
Polyamides and amidoamines: long pot life, flexibility, damp tolerance
These reaction-product hardeners trade speed for working time and toughness. Polyamides give a long pot life (often four to eight hours), a slower cure, better flexibility, and good corrosion resistance, which is why they dominate maintenance and marine coatings; the cost is a softer film and sluggish cure when cold. Amidoamines are lower in viscosity, bond well to concrete, tolerate humidity, and have lower odor, with some grades offering pot lives up to roughly 30 hours. A useful property of both is ratio latitude: they tolerate moving off the exact 1:1 stoichiometry to tune flexibility, whereas a straight amine punishes off-ratio mixing with a sharp property drop.
Mannich bases and phenalkamines: cold, wet, and fast
When the job is a cold slab or a damp marine surface, a Mannich-base curing agent is built for it. Phenalkamines, the cardanol-based (cashew-nutshell-liquid) members of this class, cure very fast even near 0 C and in the presence of moisture, resist blush, and bond to marginally prepared surfaces, while the long aliphatic side chain of cardanol adds flexibility and excellent salt-water resistance. They are the default for marine coatings, tank linings, and cold-weather industrial flooring. The honest cost is dark color and a short pot life that follows from the fast cure.
Polyetheramines: toughness and flexibility
Polyetheramine D-230, D-400, and the trifunctional T-403 (comparable to Jeffamine D-230, D-400, and T-403 grades) carry their amine groups on a flexible polyether backbone. That backbone dissipates impact energy through segmental motion, giving high elongation, ductility, and damage tolerance instead of the brittle failure of a rigid system. They cure slowly with a long pot life and clear, low color. The trade-off is a lower Tg than rigid amines, which you raise by blending with a faster amine or by post-curing with heat. They are the standard tougheners and flexibilizers, used in flooring, composites, and coatings. For grade-by-grade selection and brand cross-references, see our polyetheramine selection guide.
Aromatic amines and anhydrides: high heat, with strings attached
Aromatic amines such as methylenedianiline (MDA) and diaminodiphenyl sulfone (DDS) reach the highest glass transition temperatures, with fully cured DGEBA systems running roughly 150 to 210 C. That heat performance comes with real costs: they react very slowly and need an elevated-temperature cure, they yellow more than any other class, and at a Tg far above the use temperature the network is brittle. Several aromatic amines also carry significant occupational-exposure and regulatory controls (MDA, for example, is a substance of very high concern subject to REACH authorisation), which confines them to specialized high-temperature composite and electrical work. Anhydride curing agents, used with an accelerator and a heat cure, give low color, high Tg, low exotherm, and good electrical properties, which is why they dominate castings, potting, and filament winding; they are not amines and follow a different ratio basis.
How to calculate the mix ratio: AHEW and EEW
Epoxy is not mixed by feel or by equal volumes. Each epoxide group on the resin reacts with exactly one active amine hydrogen on the hardener, so you match equivalents, and equivalents are a mass concept. Two numbers drive the math:
- EEW (epoxy equivalent weight) of the resin: the grams of resin that contain one mole of epoxide groups. A standard liquid DGEBA resin is about 182-192 g/eq (call it 190).
- AHEW (amine hydrogen equivalent weight) of the hardener: the grams of hardener that contain one mole of reactive amine hydrogen. It equals the amine’s molecular weight divided by its number of active N-H hydrogens.
The stoichiometric ratio, expressed as parts of hardener per hundred parts of resin by weight (phr), is:
phr = (AHEW / EEW) x 100
Worked example, DETA on standard DGEBA. DETA has a molecular weight near 103 g/mol and five active amine hydrogens, so its AHEW is 103 / 5 = ~21 g/eq. With a resin EEW of 190:
phr = (21 / 190) x 100 = ~11 parts DETA per 100 parts resin, by weight.
The reason this has to be by weight, and the reason you cannot reuse one hardener’s ratio for another, is that AHEW varies enormously between classes. Run the same resin against three hardeners:
| Hardener | MW (g/mol) | Active N-H | AHEW (g/eq) | phr with DGEBA (EEW 190) |
|---|---|---|---|---|
| DETA | ~103 | 5 | ~21 | ~11 |
| IPDA | ~170 | 4 | ~43 | ~22 |
| Polyetheramine D-230 | ~230 | 4 | ~60 | ~32 |
Same resin, and the correct weight ratio swings from 11 to 32 parts. Eyeball it and you will be badly off. Off-ratio mixing is not forgiving with straight amines: excess amine plasticizes the network, lowers Tg, leaves unreacted hardener that worsens blush, and reduces chemical resistance, while excess epoxy leaves unreacted epoxide and a soft, under-crosslinked part. Always set the ratio from the actual EEW and AHEW on the certificates of analysis for the specific grades you bought, not from a generic number, and validate cure on your own system. Note that catalytic curing agents and accelerators (imidazoles, tertiary amines) do not follow this AHEW math; they are dosed at a few phr, not at stoichiometry.
Where accelerators and latent curatives fit
Two situations call for an accelerator rather than a different primary hardener. The first is a slow ambient amine (IPDA, a polyamide, a polyetheramine) that you need to gel faster or cure harder in the cold. The second is a one-component or heat-cured system that should stay inert at room temperature, then cure on demand.
DMP-30, tris(dimethylaminomethyl)phenol (comparable to Ancamine K54), is the standard tertiary-amine accelerator: a few phr sharply lowers the activation energy and speeds room-temperature cure of amine systems. Imidazoles play both roles. At low loadings 2-methylimidazole and 2-ethyl-4-methylimidazole accelerate and can themselves homopolymerize epoxy to high-Tg, low-color networks, and they are central to latent one-component formulations that are shelf-stable cold and cure fast with heat, the basis of many electronics, adhesive, and powder-coating systems. 1-Methylimidazole (NMI) is a liquid tertiary-amine catalyst used similarly and as an anhydride accelerator. Combining a tertiary amine with an imidazole is a known way to raise cure rate further. The trade-off across all accelerators is the usual one: faster cure means shorter pot life and a higher peak exotherm, so dose to the gel time and mass you actually need.
Selecting by application
- Fast ambient coatings and adhesives (warm, dry shop): an aliphatic amine (DETA, TETA) for lowest cost and hardest, fastest cure, accepting blush risk and short pot life.
- High-gloss, color-stable, weatherable coatings, flooring, and clears: a cycloaliphatic or araliphatic amine (IPDA, MXDA), or the modified IPDA adduct where blush control matters.
- Flexible, tough, impact-resistant parts: a polyetheramine (D-230, D-400, or T-403), neat for maximum toughness or blended with a rigid amine to lift Tg.
- Cold or damp jobsites, marine, tank linings: a Mannich-base / phenalkamine for cure below 10 C, in humidity, and on marginal surfaces.
- High-Tg composites and electronics: an aromatic amine or anhydride for heat resistance (accepting heat cure, slow gel, and yellowing), or an imidazole-based latent system for a shelf-stable one-component cure.
- Long working time / large pours: a polyamide or amidoamine for extended pot life, flexibility, and damp-surface and concrete adhesion.
Buying epoxy curing agents
RawSource supplies the full amine-hardener range for coatings and industrial manufacturing formulators: aliphatic amines (DETA, TETA, TEPA, AEEA), cycloaliphatic and araliphatic amines (IPDA, MXDA), the cyanoethylated IPDA adduct, polyetheramines (D-230, D-400, T-403), the DMP-30 accelerator, and imidazole curatives (NMI, 2-methylimidazole, 2-ethyl-4-methylimidazole) in drums, IBCs, and bulk with CoA documentation. Tell us your resin EEW, target cure temperature and pot life, color and Tg requirements, and toughness target, and request samples to qualify cure and ratio on your own system.
Frequently asked questions
What is the difference between an epoxy resin and an epoxy hardener?
The resin carries the epoxide rings; the hardener (curing agent) carries the reactive groups, usually amine N-H, that open those rings and crosslink the resin into a solid network. They are co-reactants, not a base plus a catalyst, which is why they are mixed at a specific weight ratio rather than a small catalytic dose. The hardener sets most of the cured properties: speed, pot life, cure temperature, color, Tg, flexibility, and blush.
How do I calculate the epoxy-to-hardener mix ratio?
Use phr = (AHEW / EEW) x 100, where EEW is the resin’s epoxy equivalent weight and AHEW is the hardener’s amine hydrogen equivalent weight (the amine’s molecular weight divided by its number of active N-H hydrogens). For a DGEBA resin at EEW 190 cured with DETA (AHEW ~21), that is (21 / 190) x 100 = about 11 parts hardener per 100 parts resin by weight. Always use the actual EEW and AHEW from the certificates of analysis for your specific grades.
Which epoxy hardener cures fastest, and which gives the longest working time?
Mannich-base / phenalkamine and unmodified aliphatic amines cure the fastest, including in cold or damp conditions for the Mannich types, at the cost of a short pot life. Polyamides, amidoamines, and polyetheramines give the longest pot life and working time, trading away cure speed. An accelerator such as DMP-30 can speed a slow amine when you need a middle ground.
What is the difference between aliphatic and cycloaliphatic amine hardeners?
Aliphatic amines (DETA, TETA, TEPA) are small, fast, low-cost, and rigid, but blush-prone and more amber. Cycloaliphatic amines such as IPDA contain a ring, cure more slowly, and deliver low yellowing, high gloss, better UV and weathering resistance, and lower blush, which is why they are chosen for high-appearance clears, flooring, and composites. Araliphatic MXDA sits between them, curing fast with high chemical resistance.
Why does cured epoxy turn yellow, and which hardeners yellow least?
Yellowing comes from oxidation of amine groups and residual reaction by-products, accelerated by UV and heat. Aromatic amines yellow the most; aliphatic amines are intermediate; cycloaliphatic amines such as IPDA and polyetheramines hold color best, which is why they are used for clears and decorative work. No amine-cured epoxy is fully UV-stable, so a UV-exposed clear is usually protected with a separate weatherable topcoat.
Which epoxy hardener gives the highest heat resistance (Tg)?
Aromatic amines (MDA, DDS) and anhydride curing agents give the highest glass transition temperatures, with fully cured aromatic-amine DGEBA systems reaching roughly 150-210 C, but they require an elevated-temperature cure and tend to be brittle, and aromatic amines yellow and carry heavier regulatory controls. Among ambient-cure amines, MXDA and cycloaliphatic IPDA reach the higher Tg values, and any system’s Tg rises with a post-cure at elevated temperature.
Editorial note. This article is general technical guidance for coatings, adhesive, composite, and industrial formulation professionals. Cure speed, pot life, Tg, color, flexibility, blush, and the correct mix ratio depend on your specific resin, hardener grade, ratio, film thickness or mass, and cure environment, and must be validated on your own system; the Certificate of Analysis governs the EEW, AHEW, and grade you buy. Brand names (Jeffamine, a Huntsman product; Ancamine, an Evonik product) are used only nominatively to identify comparable chemistries; no affiliation or endorsement is implied. Amine hardeners are corrosive and can cause skin and eye burns and skin and respiratory sensitization, and several aromatic amines carry additional regulatory restrictions; review the current Safety Data Sheet (SDS) and use appropriate PPE before handling. Products are sold for industrial and professional use only. Nothing here is a medical, health, or safety claim. RawSource makes no warranty, express or implied, and assumes no liability for use of this information.
