Soft spots, sticky patches and cloudy pours usually trace back to one thing: the mix. Epoxy is a chemical reaction between resin and hardener, and it only cures properly when both parts are measured and mixed correctly.
- Use the exact ratio on your product’s label, and only measure by weight if the maker gives a weight ratio.
- Mix slowly and thoroughly, scraping the sides and bottom of the cup.
- Pour soon after mixing. A full cup of mixed epoxy heats up and cures faster.
1. Read the ratio, and how it’s measured
Ratios vary by product: 1:1, 2:1, 3:1, 5:1 and others are all common. Some products give a ratio by volume, some by weight, and the two are often not the same, because resin and hardener have different densities. Use whichever the manufacturer specifies. Adding “a bit extra hardener” will not make epoxy cure faster; it leaves unreacted material and a soft or sticky result.
2. Measure accurately
- By volume: use clear, graduated mixing cups and read at eye level. Or use calibrated pumps if your system offers them; manufacturers such as WEST SYSTEM sell metered pumps for their resin and hardener (see the WEST SYSTEM User Manual & Product Guide).
- By weight: use a digital scale, tare the cup, and add each part slowly.
- Measure fresh for each batch. Don’t eyeball.
3. Mix (longer than you think)
- Stir slowly with a flat stick or paddle for the time your product’s instructions give, usually a few minutes.
- Scrape the sides, the bottom, and the corners of the cup repeatedly. Unmixed resin hides there.
- Two-cup method: pour the mixed epoxy into a second clean cup and mix again with a clean stick. This leaves any unmixed material behind in the first cup.
- Stir slowly to avoid whipping in air. See how to prevent epoxy bubbles.
4. Mind the heat
Curing epoxy gives off heat. A large mass of mixed epoxy in a cup heats up much faster than the same amount spread thin, which can shorten working time drastically. Pour promptly after mixing. For thick pours, use a deep-pour product and follow its maximum pour depth. See deep-pour epoxy for river tables.
5. Temperature matters
Cold resin is thick, hard to mix and traps bubbles. Store resin and hardener at room temperature before use, and work in the temperature range on the label. See curing epoxy in cold weather.
Safety
Wear nitrile gloves and eye protection, and work with good ventilation. Some resin products can release volatile chemicals; the EPA: Volatile organic compounds’ impact on indoor air quality explains why ventilation matters indoors. More: epoxy safety basics.
Still sticky after curing? Here’s how to fix it.