How to use this guide
This guide helps procurement, EHS, and formulators align on the right curing agent family for a target application (flooring, protective coating, adhesive, composite, or repair mortar). The hardener is not just a “reactant” — it defines your usable working time, cure profile, surface tolerance, and a large share of the final mechanical/chemical resistance.
What “selection” really means
- Performance: adhesion, flexibility, chemical/solvent resistance, heat resistance, gloss/appearance, water spotting.
- Application: pot life, viscosity, wetting, tolerance to damp surfaces, recoat window, cure in cold conditions.
- Reliability: mix ratio sensitivity, blush/carbonation risk, batch-to-batch consistency, shelf life.
- Commercial: supply stability, packaging, hazards/labeling, and documentation readiness (SDS/COA).
Where it fits
- Typical systems: Bisphenol-A/F epoxies, novolac epoxies, reactive diluents, fillers/pigments, and additives.
- Applications: anti-corrosion primers and topcoats, tank linings, flooring (self-leveling, mortar, screed), adhesives/anchoring, composites, concrete repair.
- Constraints: VOC limits, cure temperature limits, humidity, substrate moisture, food-contact or potable-water requirements, and site EHS rules.
Fast decision map
Use the table below as a first-pass filter. Final choice should be validated with small-scale trials under realistic temperature and humidity.
| Curing agent family | Typical strengths | Common watch-outs | Best-fit use cases |
|---|---|---|---|
| Aliphatic amines e.g., TETA/DETA blends, modified amines |
Fast cure, strong early hardness, good adhesion | Blush risk, moisture sensitivity, higher odor/irritancy, short pot life | Fast-turnaround repairs, shop-applied systems (controlled conditions) |
| Cycloaliphatic amines often clearer, better aesthetics |
Better color stability, good hardness, balanced cure | Cost, may need warmer cure for full properties | Decorative floors, clear coats, color-sensitive coatings |
| Polyamides fatty-acid polyamides |
Flexibility, impact resistance, surface tolerance, longer pot life | Lower chemical/solvent resistance vs high-crosslink systems, slower cure | Primers, maintenance coatings, adhesive systems needing toughness |
| Phenalkamines cashew-derived backbone variants |
Very good damp surface tolerance, fast cure at low temperature, good corrosion resistance | Potential color, odor, formulation compatibility checks needed | Marine/maintenance, damp concrete, cold-weather field application |
| Aromatic amines high-performance curing agents |
High Tg/heat resistance, excellent chemical resistance | Slow at ambient, often needs heat, color/darkening, hazard profile | High-temperature service, aggressive chemical environments (when permitted) |
| Anhydrides typically heat-cured |
Very high electrical properties, low exotherm, good heat resistance | Needs elevated cure, catalysts, process control | Electrical encapsulation, composites, controlled manufacturing |
Key decision factors
- Application temperature & humidity: pot life and cure speed change drastically between 10°C and 30°C; humidity affects blush and surface defects.
- Target cure profile: “walk-on” time, sand/recoat window, full chemical resistance time, and maximum allowable downtime.
- Final properties: hardness vs flexibility, abrasion resistance, adhesion, and chemical resistance class (acids/alkalis/solvents).
- Substrate & surface condition: steel vs concrete; blasted profile; moisture; contaminants; surface prep capability on site.
- Mixing realities: manual mixing vs metering; risk of ratio error; batch size; heat build-up (exotherm).
- Regulatory/EHS: sensitizers, corrosives, VOC, labeling, and site acceptability.
Stoichiometry basics (how mix ratio is determined)
Epoxy cure is not “add a little extra hardener for speed.” Most systems are designed around near-stoichiometric reaction. Getting ratio wrong often shows up as soft cure, poor chemical resistance, amine sweat, blush, or brittleness.
Key terms you’ll see on technical data
- EEW (Epoxy Equivalent Weight): grams of epoxy resin containing one equivalent of epoxide groups.
- AHEW (Amine Hydrogen Equivalent Weight): grams of curing agent containing one equivalent of reactive amine hydrogen.
- Theoretical mix ratio: computed from EEW and AHEW; suppliers often provide recommended ratio by weight and by volume.
Practical ratio rules
- Always specify whether ratio is by weight or by volume (density differences can be large).
- Define acceptable ratio tolerance (e.g., ±2–3%) based on metering capability.
- For field kits, request packaging that enforces ratio (pre-measured packs) when possible.
Pot life, gel time, and exotherm (what changes in real production)
Pot life is not a single number — it depends on mass, container geometry, mix temperature, and whether you pour out the mix quickly. Larger batches self-heat, accelerating cure (runaway exotherm).
- Pot life (working time): time you can apply the mixed system before viscosity rises too much.
- Gel time: time to initial gelation under test conditions (useful for comparing hardeners).
- Exotherm control: mix smaller batches, use wider trays, avoid leaving mixed epoxy in deep pots.
- Temperature sensitivity: as a rough rule, higher temperature dramatically speeds cure; always validate at your lowest expected site temperature.
Blush and surface defects (why “it cured but failed”)
Many amine-cured epoxies can form amine blush (a waxy/greasy film) under humidity and low temperature. Blush can cause intercoat adhesion failure, cratering/fisheyes, or hazy appearance.
- Blush risk increases with: high humidity, low temperature, poor ventilation, excess amine, and slow cure.
- Mitigation: choose low-blush or modified amines, control conditions, wash/sand before recoating, and keep ratio accurate.
- Pinholes/foaming: can come from substrate outgassing (warm concrete), high viscosity, or aggressive solvents.
Choosing by application (quick guidance)
Protective coatings (steel, maintenance)
- Priority: adhesion, corrosion resistance, recoat window, surface tolerance.
- Often fits: polyamides or phenalkamines (field-friendly); cycloaliphatics (aesthetic systems); higher-crosslink amines for chemical service.
Flooring (concrete, industrial)
- Priority: pot life vs install speed, wetting/self-level, blush control, abrasion resistance.
- Often fits: modified amines/cycloaliphatics; phenalkamines for cold/damp conditions; check compatibility with pigments/fillers and slip additives.
Adhesives/anchoring
- Priority: toughness, bond strength, cure speed at site temperature, and ratio robustness.
- Often fits: toughened/modified amines or polyamides; consider thixotropy and sag control.
Composites & electrical (controlled manufacturing)
- Priority: Tg, heat resistance, electrical properties, low exotherm in thick sections.
- Often fits: anhydrides (heat-cure) or specialized amines; tightly controlled cure schedule.
Specification & acceptance checks
When comparing curing agents, ask for data you can verify on receipt and that correlates with performance:
- Identity: product name/grade, manufacturer, batch/lot traceability.
- Key QC items (typical): amine value / total amine, viscosity at stated temperature, color (Gardner/APHA), density, water content (where relevant).
- Reactivity indicators: gel time at defined conditions; pot life guidance with a reference resin (if available).
- Compatibility notes: recommended epoxy types (BPA/BPF/novolac), pigments/fillers, reactive diluents, solvents.
- Packaging: drum/IBC, lining, closures, nitrogen blanketing if applicable, labeling.
- Safety: current SDS, hazard statements, sensitization/corrosivity notes, PPE requirements.
- Storage: shelf life, temperature limits, crystallization/cloud point guidance, FIFO requirements.
- Logistics: lead time, Incoterms, availability of consistent grades, and change-control expectations.
Handling & storage
- Moisture control: keep containers sealed; moisture pickup can affect reactivity and blush behavior.
- Temperature: store within supplier range; warm gently (per SDS) if viscosity rises in cold weather.
- Contamination: use dedicated pumps/hoses; avoid cross-contamination with acids or oxidizers.
- EHS basics: many curing agents are skin sensitizers and/or corrosive—use gloves, eye/face protection, and ventilation.
Troubleshooting signals
If performance drops, these are common early indicators and what to check first:
- Soft or tacky cure: ratio error, poor mixing (scrape sides/bottom), low temperature, expired material, moisture contamination.
- Short pot life / runaway heat: batch too large, high starting temperature, fast hardener chosen, deep container geometry.
- Blush / greasy film: humidity + low temperature, excess amine, slow cure, poor airflow; wash/sand before recoat.
- Cratering/fisheyes: surface contamination (silicones/oils), incompatible additives, blush residue, improper solvent choice.
- Adhesion failure: surface prep, blush, outgassing, too long/short recoat window, undercure.
If you share your resin type (EEW), target cure schedule, site temperature/humidity, and symptoms, we can usually narrow down the likely cause quickly.
RFQ notes (what to include)
- Application: coating/flooring/adhesive/composite; substrate type; film thickness or casting thickness.
- Operating conditions: temperature range, humidity, outdoor/indoor exposure, chemical splash list.
- Targets: pot life, tack-free time, recoat time, full cure time, and final property priorities (hardness vs flexibility vs chemical resistance).
- System info: epoxy resin type and EEW; pigments/fillers; VOC limits; any reactive diluent constraints.
- Process: manual vs metered mixing; batch size; packaging preference (kits/drums/IBC).
- Commercial: monthly volume, destination country, documentation requirements (COA/SDS), and change-control expectations.
Need a supply-ready shortlist?
Tell us your epoxy resin type, temperature/humidity conditions, and target pot life + cure time. We’ll propose curing agent options (family + grade), with SDS/COA expectations and procurement-ready specs.
Educational content only. Always follow site EHS rules and the supplier SDS/technical data for safe handling and use. Validate formulation changes with controlled trials before production.