TotalBoat Underwater Repair Epoxy has to be applied under normal ambient temperature conditions in order for it to cure properly. Keep in mind that it's an epoxy-based product, so the warmer the temperature, the shorter the working time and cure time will be. On the lower end of the temperature scale, 50°F is the general lower limit for getting the exothermic (heat-producing) reaction to happen at a reasonable rate. If the water is less than 50°F, the product will take a very long time to cure.