Two Part Epoxy: How 2-Part Systems Work & Which to Use
Updated 17 October 2026
Almost every epoxy you can buy, from a tiny syringe of glue to a 30-litre river table kit, is a two part epoxy. One container holds the resin, the other holds the hardener, and nothing happens until you combine them. That simple idea hides a lot of variation: mix ratios of 1:1, 2:1 or 3:1, pot lives from five minutes to several hours, and cure profiles designed for anything from bonding metal to casting a 10 cm slab. This guide explains how 2-part systems work, why the ratio matters so much and how to pick the right one for your project.
For the wider picture of resin types and uses, see our epoxy resin hub.
How a two part epoxy system works
Part A is the epoxy resin itself, a liquid containing reactive epoxide groups. Part B is the hardener (also called the curing agent), usually based on amines. When they are mixed, each hardener molecule links to several resin molecules, building a three-dimensional cross-linked network. As that network grows, the liquid thickens into a gel and then into a hard solid.
Two consequences follow:
- The ratio is fixed by chemistry. Resin and hardener are formulated to react in specific proportions. Extra hardener does not make it cure faster; it leaves unreacted chemicals that make the result soft, sticky or brittle.
- The reaction gives off heat (exotherm). The more mixed resin sits in one mass, the hotter it gets and the faster it cures. That is why thick pours need specially slow formulas.
Single-part alternatives do exist, such as UV resin, which cures under ultraviolet light instead of with a hardener, but these are limited to thin layers.
Mix ratios: 1:1 vs 2:1 vs 3:1
| Ratio (resin:hardener) | Typical products | Typical working time | Typical max pour per layer | Best for |
|---|---|---|---|---|
| 1:1 | Coating, table top and bar-top resins, many craft resins, quick glues | 20–45 minutes | 3–6 mm | Flood coats, sealing, small art |
| 2:1 | Casting and deep pour resins, laminating systems | 40 minutes to several hours | 25–50 mm or more | River tables, moulds, thick castings |
| 3:1 or higher | Very slow deep pour casting resins, some marine systems | Hours | 50–100 mm, depending on product | Large single-pour castings |
Always check whether the ratio is by volume or by weight. Resin and hardener have different densities, so a 2:1 ratio by volume is not 2:1 by weight. Mixing by weight on digital scales is the most accurate method for anything more than a small batch.
Pot life, working time and cure time
- Pot life is how long a mixed batch stays usable in its container before it thickens. Because heat builds up in a cup, pot life is shorter than the time the resin stays workable once spread thin.
- Working time (open time) is how long it remains liquid enough to level, spread or self-release bubbles after pouring.
- Cure time is usually given in stages: tack-free, demouldable or handleable, and full cure, which is often 3–7 days at around 20–25°C.
Temperature has a big effect. As a rough rule, a 10°C rise in temperature roughly halves the working time, and a 10°C drop roughly doubles it. Below about 15°C many epoxies cure slowly and may stay tacky or develop amine blush.
Choosing a 2 part epoxy by project
Coating a tabletop or bar top
A 1:1 self-levelling coating resin is the usual choice, applied around 3 mm per coat. See table top epoxy for what to look for.
River tables and deep castings
Use a slow 2:1 or 3:1 deep pour resin and never exceed its maximum layer thickness. Our deep pour epoxy guide explains why exotherm control matters, and the epoxy volume calculator helps you work out how much to buy.
Woodwork, repairs and filling
Two part epoxy for wood comes in several forms: thin penetrating sealers, gap-filling adhesives and thickened putties. Our guide to choosing epoxy for wood compares them, and epoxy wood filler covers repairing rot, knots and holes.
Floors and protective coatings
Floor and industrial systems are also 2-part, but formulated for adhesion to concrete and abrasion resistance rather than optical clarity. See epoxy coating for an overview.
Clear art and embedding
For glass-like results, choose a low-colour resin with UV stabilisers. Our guide to clear epoxy resin explains how to avoid bubbles, haze and yellowing.
How to mix two-part epoxy correctly
- Condition the bottles to around 20–25°C; warm thick resin in a water bath.
- Measure precisely using graduated cups or scales, according to the ratio printed on the label.
- Mix for the full time, typically 3 minutes for small batches and longer for large ones, scraping the sides and base repeatedly with a flat stick.
- Transfer to a second container and mix again briefly, so unmixed resin clinging to the first cup does not end up in your work.
- Pour promptly. Spreading the mix out, rather than leaving it in a deep cup, slows the exotherm and extends working time.
Mixing mistakes cause most failures: soft spots, sticky patches and streaks are almost always caused by an incorrect ratio, poor scraping or a cold room. If you are just starting out, our epoxy resin for beginners guide covers set-up step by step.
Storage and shelf life
Unopened kits typically keep for around one to two years if stored sealed, upright and at a steady room temperature away from sunlight. Hardeners slowly darken with age and air exposure, which matters for clear work, so replace lids promptly and write the opening date on each bottle. Resin stored in a cold garage can crystallise and turn cloudy or grainy; warming the sealed bottle in hot water until it clears usually restores it. Never mix a fresh hardener with old resin from a different system.
Safety
Both parts can irritate skin, and the hardener in particular is a known sensitiser: repeated contact can trigger allergic dermatitis that is permanent. Wear nitrile gloves, long sleeves and eye protection, work in a ventilated space, and clean skin with soap and water, never solvents. The Irish Health and Safety Authority’s epoxy resins information sheet summarises the health effects and controls. For the chemistry of hardeners and cross-linking in more depth, see Wikipedia’s article on epoxy.
Disposal: never pour unmixed resin or hardener down the drain. Mix small leftovers together and let them cure fully, after which the solid can usually go in general waste; take larger quantities of liquid to a household hazardous waste site.
Watch it being made
Watch our first light-up resin table being made in the workshop, with dragons and creatures appearing in the resin art, and the colours, pours and finishing shown step by step.
Resin Art Dragons and creatures in resin art table My First Light-Up Resin Table. More builds on the Go Bespoke YouTube channel.
Frequently asked questions
What is 2 part epoxy used for?
Almost everything epoxy does: gluing, filling, coating, laminating, casting and floor coatings. The specific formulation determines whether it suits thin coats, thick pours or structural bonding.
What happens if you get the two part epoxy resin ratio wrong?
The cure will be incomplete. Too much of either part leaves soft, sticky or rubbery areas that will not harden with time. The only fix is to scrape off the uncured material and pour again.
Is 1:1 or 2:1 epoxy better?
Neither is better overall. 1:1 systems are convenient for thin coats; 2:1 and 3:1 systems are generally slower and designed for deeper pours with less heat build-up.
How long does two-part epoxy take to cure?
Typically tack-free in 6–24 hours and fully cured in 3–7 days at room temperature. Deep pour resins can take longer before they are ready to demould and sand.
Can you use 2 part resin without measuring exactly?
No. Eyeballing the ratio is the most common cause of failed pours. Use marked cups or scales every time.
Want to see two-part systems used on real builds? Watch resin pours and table builds on the Go Bespoke YouTube channel.
