Taught by a cadweld master-10 years ago.
Make sure all the condensation is out of the mold and out of everything. keep a propane torch with you pre-heat the wire, the rod and whatever else. Every component has to be at the same teperature. Throw out the shots that aren't loose, or might have water or condesation. get those toothpaste wire brushes to get rid of that crap in the weld, clean it every shot.
Made great molds 50 below in Wainwright , AK. Can do it anywhere else.
Bl Brnnr, 71, lineman stud taught me, and will never forget.