Working time (also called working life) indicates how much time you have to work with the mixed epoxy resin (resin and hardener combined) before it kicks, or becomes so viscous that you can no longer work with it.
Epoxy manufacturers define working life with a reasonable safety factor built in so you know how much time you have to properly work with and handle the mixed resin.
When the resin and hardener components are combined together, it produces an exothermic (heat-producing) reaction. The greater the volume of the mixture, the greater the reaction between the molecules, the more heat generated—and the faster the mixture will kick.
There are a few things you can do to extend the working time for epoxy resin by slowing down the reaction between the molecules, which will reduce rate of exotherm.
- Reduce how thick the mixed volume is by adding it to a wider diameter mixing pot.
- Cool down the mixed material by putting the mixing pot in cool (not cold!) water.
- For large amounts of mixed resin, pour it out over the surface before spreading it around with an epoxy spreader.
- If working with thickened epoxy, such as a fairing compound, use a mixing stick to spread the mixture evenly around the inside of the mixing cup, to reduce its thickness.