I use an epoxy system specifically designed for ski and snowboard applications by QCM Industrial, a local company. The epoxy is designed to be flexed and resist impact at extremely low temperatures. The epoxy resin (EMV-0049) and hardener (ECA-032) are measured out and weighed to the gram, then mixed thoroughly. The boards are pressed with carefully controlled heating, on the top and bottom of the board, to cure the epoxy properly so it will develop its full properties. The manufacturer recommends a heated cure of 180F for this particular epoxy system.
Whenever you get a new batch of epoxy you should label the cans and always use them in sets. Mix a 100g test sample, cure it properly, and do a basic stress test on it (i.e., break it). Ensure it behaves as you expect, and as it has for you in the past. One time I got a can of resin that was incorrect, and the 100g sample showed the problem immediately. I took the cans and the sample back to the manufacturer, and they apologized and replace it right away.
If you’re selling your boards or skis, I highly recommend recording which batches of epoxy you use in each build. Save the tests so you can refer back to them if someone reports a problem.
Every epoxy system is different: some are measured and mixed by volume, and some are measured by weight. It is important you know which way you should measure for your epoxy. Mixing by volume with epoxy that needs to be mixed by weight will result in either too much hardener (and it will kick too fast) or too little, in which case the epoxy will not cure properly.
I use a “two-cup” mixing method. I use two cups which are individually large enough to hold the entire volume of mixed epoxy. I measure out the hardener into Cup A and the resin into Cup B. I pour the hardener from Cup A to Cup B, and mix thoroughly in Cup B. I then pour Cup B into Cup A, being careful to scrape the bottom and sides of Cup B to make sure I get any un-mixed resin out. I then continue to mix in Cup A. This ensures that no resin is left on the bottom of Cup B.
A good trick you can use to help you learn if you’re mixing well or not is to add a very small amount of pigment to your hardener before you start mixing. Pickup a small bottle of epoxy pigment and put just a smidge (dab the tip of a tongue depressor in it) into the hardener and mix will. Now when you mix the hardener with the resin you will see easily any unmixed resin. This small amount of pigment will not appreciably color your final mix of epoxy, and will be unnoticeable in your final board.
There are two safety aspects to be concerned about: fire, and long-term sensitivity.
Epoxy cures via an exothermic reaction. That means it generates heat while it cures, and as it gets warmer it generates more heat. Given enough epoxy and heat this reaction can “run away” and generate an amazing amount of heat, enough to ignite the epoxy or whatever it is near. Needless to say, that’s bad. Even if it doesn’t ignite it can smolder and generate a toxic smoke that you should avoid.
Leftover epoxy should simply never be left in a cup when you are done with it. Pour it out onto a plastic picnic plate or something equally disposable and let it cure slowly in a thin film. Never leave a cup with even an inch of epoxy in the bottom sit to cure on its own, or toss such a cup in the trash, etc.
You should keep epoxy off your skin, and avoid inhaling epoxy dust as you process your board or skis after pressing. Some people can develop a sensitivity to the chemicals in epoxy with repeated exposure over a long period of time. This can cause skin rashes or breathing problems when exposed to a minimal amount of epoxy, and essentially leave you in the position of not being able to work with it again.
Rubber gloves, long-sleeve work shirts, and simple dust masks are your friends here. Use them every time.