Epoxy Mix Calculator — Resin & Hardener Ratios

Incorrect ratios result in epoxy that either never fully cures (too much resin), cures too quickly and becomes brittle (too much hardener), or remains tacky indefinitely. Always measure carefully and follow the manufacturer's specified ratio.

Check your product instructions. Many epoxies specify mixing by volume, but some are measured by weight. Resin and hardener have different densities, so the ratios differ between volume and weight measurements. When in doubt, use the method specified on the packaging.

No. Pot life is set by the hardener chemistry (fast, standard or slow), the batch mass and the temperature — not the resin-to-hardener ratio. A 1:1 epoxy can be a 5-minute hardware-store glue or a 45-minute structural system; both West System 105/205 (Fast) and 105/206 (Slow) share the same 5:1 laminating ratio yet the 205 Fast gels in about 9-15 minutes for a 100g batch while the 206 Slow gives around 20-25 minutes — same ratio, very different working time. Choose the hardener speed to suit the job, then size the mix.

Spread the mixed epoxy into a thin layer on a flat surface rather than leaving it in a cup. The mass of epoxy in a container generates heat that accelerates curing. Working in cooler temperatures also extends pot life — every 10°C drop roughly doubles your working time. Switch to a slow hardener for large glue-ups. Never add solvent to slow the cure.

Yes, epoxy is excellent for gap filling. Mix in wood dust or commercial thickeners to create a paste-like consistency. For structural gap filling, use a slow-set epoxy (30+ minute pot life) to allow full penetration into the wood fibres.