Exothermic welding looks very easy and it is, until it isn't. There are times when the welds don't stick, or the weld material all runs out on the ground. There are simple solutions to most of the problems associated with Cadwelding.
A new mold is great to work with. If it is taken care of properly, it will give long term satisfactory use. Do not clean your molds with wire brushes, screwdrivers, pliers or anything that will scratch the mold. These scratches are the start of the deteriorating effects. The weld material doesn't flow properly, the mold doesn't fit snuggly, harder each time to clean it out. The mold manufacturers sell brushes specifically designed to clean the molds. For the price of one mold, you can buy 18 brushes.
Properly cleaning the wire and surface to be welded to are just as important. Impurities have a negative effect on the welds. Make sure all the dirt, oil, grease, water, etc. have been removed.
Pre-heating the wires and/or metal surface before attempting to shoot a weld aids in the welding process. If the wires or metal surface are too cool the welds won't stick.
Sloppy molds are difficult to use, but we have all had to use them at one time or another. To stop the weld material from running out, Cadweld sells mold sealer (looks exactly like duct seal). I have found this doesn't work very well and leaves a sticky mess on the mold. I prefer to get the mold set and then pack moist dirt around the mold. The cool wet dirt makes the weld material cool faster and stops the flow. Duct seal just melts and creates a bigger mess.
Cadweld also sells copper strips that can be used to increase wire size. For example, you have a 4/0 run & tap mold but you need to tap off your 4/0 with a 2/0. These copper strips are wrapped tightly around the end of the wire increasing the 2/0 to the same diameter as the 4/0. Much easier than cutting small strands of wire and trying to fit them in the mold. The strips save time, which saves money.
