Gary, the west system manual will tell you which hardener to use according to the temperature of your work area. When you buy the resin, you buy metering pumps that make mixing very easy, and you buy the additive(powder) to mix up the fairing compound. There is a different powder to use if you are making glue. Always prime with clear mixed resin before you apply the fairing compound. The manual is very clear, and overall it is an easy product to use.____Grant.