Originally Posted by
speedracerntrixie
Yes for a full cure and for the epoxy to reach full strength it must be cured above 70 degrees. At work we cure all epoxies at 160 degrees or higher ( I'm a composites tech by trade ). For your application as long as you get enough cure to keep fuel from invading the molecular structure of the epoxy you will be fine. After initial application warm it up with a hair dryer and continue to do so one every hour until the epoxy is tack free. If you are building in a cold environment your glue joints will not be as strong as they would be had the epoxy been cured at a higher temp. Not to worry, the elevated temps of being transported in your car and sitting in the pits will take care of that and actually perform a post cure of sorts.
I'm going to disagree with you on some points of your post:
1)
for a full cure and for the epoxy to reach full strength it must be cured above 70 degrees
2)
If you are building in a cold environment your glue joints will not be as strong as they would be had the epoxy been cured at a higher temp
Per the West Systems website:
Each hardener has an ideal temperature cure range. At any given temperature, each resin/hardener combination will go through the same cure stages, but at different rates. Select the hardener that gives you adequate working time for the job you are doing at the temperature and conditions you are working under. The product guide and container labels describe hardener pot lives and cure times.
At no time does the manufacturer make any reference to strength and heat being inter-related. In fact, the website actually states:
CAUTION! Heating epoxy that has not gelled will lower its viscosity, allowing the epoxy to run or sag more easily on vertical surfaces. In addition, heating epoxy applied to a porous substrate (softwood or low-density core material) may cause the substrate to "out-gas" and form bubbles in the epoxy coating. To avoid out-gassing, wait until the epoxy coating has gelled before warming it. Never heat mixed epoxy in a liquid state over 120°F (49°C).
In a commercial manufacturing application, the chemical makeup of the epoxies used are different than what we as consumers and modelers will have access to through common sources. Years ago, I was working at Hexcel where we used pre-preg materials with varying epoxy compounds in the fabrication of aircraft parts. To increase strength and decrease cure time, the parts were vacuum bagged to 29" of vacuum and baked in an oven slightly hotter than you indicated. The vacuum bagging was what increased the strength, compressing the fabrics more tightly together and removing almost all of the air in and between the plys. The heat only decreased cure time and melted the epoxy coating so that it could flow between the fibers and actually "grab" the fabric plies, holding them together and filling the weave to make a solid, windproof surface.