ORIGINAL: Rodney
what pdm52956 said, if you are mixing in anything with a wax coating the epoxy may not set up properly. I have never had a problem with any of the epoxys not setting up properly, even if the mix ratio was off quite a bit. Temperature effects cure time a lot, the warmer the faster up to a point well above what a human can stand.
I go down to a restrant supply place and pick up a sleve of 1oz plastic cups, those cheep things that the take out resturants put condiments in. A sleeve of 100 cost me about $3.00. Them and a box of long round sticks, "hardwood aplicators" that came from a medical supply. Each epoxy get mixed in a new cup and with a new stick. No contamination at all, and the cost is about four cents per batch.
On the heat, you need to keep the epoxy below 140F. Cured epoxy starts to break down a 150F or so. I try to keep it down to about 120F maxum. At that temp, you can cure epoxy without a hardner, almost.
Don