Locate the crack in the cast iron and bevel it halfway through the thickness of the wall. With a file or grinder, clean the scale from the cast iron 13 mm on either side of the crack.
BE SURE TO DRILL A SMALL HOLE JUST BEYOND BOTH ENDS OF THE CRACK TO STOP THE CAST IRON FROM FURTHER CRACKING AS HEAT IS APPLIED.
In the center of the crack, drill a hole and tap it to accept a 6 mm cap screw. Screw the cap screw up to the thread ends. To leave a flush surface, be sure to saw off the excess screw. (The bolt will keep the crack from "breathing" and will prevent the movement of the cast iron when heat is applied).
Dry crack with a oxy-acetylene torch. (Be careful to not heat above 330 degrees F). Drying the crack prevents water from interfering with the cast iron weld.
Using a back-step procedure, weld the cast iron. Start 2 inches from one end of the crack and weld to end. Then step back 2 inches and weld into proceeding weld. Continue until weld is completed. This procedure helps to eliminate the stress cracking normally attributed to heat travelling in front of the weld.
