Epoxy can remain soft if the resin and hardener are measured at the incorrect ratio or are not mixed thoroughly. Always follow the specified mixing ratio and mix the resin and hardener thoroughly for 2 to 3 minutes, scraping the sides and bottom of the mixing container as you work.

The two-cup mixing method can help ensure a more thorough mix. After initially mixing the resin and hardener, transfer the epoxy to a second clean mixing cup and mix again before applying. This helps prevent unmixed material from the sides or bottom of the first container from being applied to the project.

Cold temperatures can also slow the curing process and extend the amount of time required for the epoxy to harden.