Epoxy cures through a chemical reaction, and that reaction slows sharply as temperatures fall. In a cold garage or shop, a pour that should be hard by tomorrow can stay tacky for days, or never cure right.
Check the data sheet first
Every product lists a minimum application and cure temperature on its technical data sheet (TDS). Many coating and casting resins want the room, the resin, and the surface all around 70–80°F, and some floor systems list a minimum surface temperature too. Treat the TDS as the rule, not general advice.
Keep everything warm
- Warm the resin and hardener indoors for a day before using them. Cold resin is thick, traps bubbles, and mixes poorly.
- Warm the space ahead of time and keep it warm through the full cure. A cold slab of concrete pulls heat out of a floor coating.
- Use dry heat. Unvented propane or kerosene heaters add moisture and CO2, which can cause amine blush (see our amine blush guide).
- Mind the dew point. If the surface is near the dew point, moisture can condense under the coating. Many floor-coating makers say the surface should be at least 5°F above the dew point.
Don’t overcorrect
Too much heat is a problem for deep pours. Thick river-table pours generate their own heat, and warming them can cause cracking, yellowing, or a runaway reaction. Follow the maximum pour depth for your product (see deep pour epoxy).
Common cold-weather mistakes
- Adding extra hardener to “speed it up.” This ruins the ratio and leaves soft spots.
- Turning the heat off overnight.
- Coating a cold, damp slab.
Measure your project carefully and buy a little extra resin.