Epoxy is a two-part thermosetting system: resin and hardener react in a specified ratio to form a cured plastic. Reliable results come from treating metering, temperature, mixing, surface preparation and cure as one controlled process.
This guide explains the shared fundamentals. The instructions for the exact resin, hardener, coating or adhesive always take priority because mix ratios, pot life, recoat windows and suitable substrates vary.
Quick answer
Choose the epoxy system for the job, prepare a clean and sound substrate, meter the exact ratio, mix thoroughly, transfer or apply before the working time expires, and protect the work through full cure.
What you need to know
- Ratio is chemistry, not a way to adjust cure speed.
- Pot life is measured in a defined mass; a deep pail heats and cures faster than a thin film.
- Secondary bonding depends on clean, properly prepared surfaces.
- Fillers are selected for bonding, filleting, fairing or coating—not added at random.
- Cure time changes with product, hardener, mass and temperature.
Tools and materials
- Exact epoxy resin and compatible hardener
- Current technical data sheet and SDS
- Calibrated pumps or accurate scale approved for the system
- Clean straight-sided mixing pots and stir sticks
- Surface-cleaning and abrasion tools
- Selected fillers, fabric or reinforcement where required
- Application tools and suitable PPE
Step-by-step method
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Define the job
Decide whether the epoxy must bond, coat, laminate, fill or fair. Note the substrate, temperature, exposure, load and desired finish before choosing resin, hardener and filler.
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Prepare the surface
Remove contamination, weak material and gloss by the method approved for the substrate. Vacuum dust and complete any solvent cleaning before mixing.
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Condition and stage
Bring materials and the work into the permitted temperature range. Lay out tools, reinforcement and an exit plan so the mixed batch is not left waiting.
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Measure accurately
Use the manufacturer's pumps or ratio by weight or volume. Do not add extra hardener to speed the cure and do not estimate partial kits by eye.
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Mix completely
Scrape the sides, bottom and corners while mixing for the specified time. For critical work, transfer to a clean second pot and mix again if the instructions permit.
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Apply within the working time
Spread the epoxy promptly. A roller tray or thin film dissipates heat better than a deep mixing cup. Wet out reinforcement fully without flooding it.
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Control the cure
Keep the work within the required temperature and protect it from water, dust and movement. Observe the recoat window or wash, abrade and clean cured epoxy as directed.
Common mistakes
- Changing the resin-to-hardener ratio
- Mixing a batch larger than the stated limit
- Bonding over oil, dust, oxidation or an unknown coating
- Adding filler before resin and hardener are fully mixed
- Assuming tack-free epoxy has reached full strength
- Using a coating epoxy where a structural adhesive is required
Safety and limits
Epoxy components can irritate or sensitize skin. Avoid contact, provide ventilation and use the PPE required by the SDS.
A curing batch generates heat. Do not leave mixed epoxy in a large mass or dispose of reacting material in a way that can overheat.
Frequently asked questions
Can I add more hardener to make epoxy cure faster?
No. Use the exact ratio. Choose a faster compatible hardener or warmer approved conditions instead.
Why did my epoxy stay soft?
Common causes include an incorrect ratio, incomplete mixing, low temperature or incompatible contamination. Remove uncured material and diagnose the cause before recoating.
When should filler be added?
Mix resin and hardener completely first, then blend in the selected filler until the mixture reaches the required consistency.
Can epoxy bond every plastic?
No. Low-surface-energy plastics such as polyethylene and polypropylene require special treatment and testing, and some applications need a different adhesive.
Get the right materials for the job
Tell our team what you are making, what materials are involved and how the finished result will be used.
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This guide provides general educational information. Products, substrates, site conditions and regulations vary. Follow the current technical data sheet, package directions and safety data sheet for every product you use. Code-regulated, structural or safety-critical work may require a qualified professional.