A mold includes a weld cavity, housings for the components to be welded, a crucible-funnel in communication with the weld cavity for housing filling material, at least one additional cavity for housing an exothermic mixture; and an inner shell that separates the crucible-funnel and the at least one additional cavity to transmit heat produced in the exothermic reaction from the additional cavity to the crucible-funnel. The mold allows the exothermic mixture to be isolated to avoid contact with the filling material and to prevent the filling material from reaching the weld cavity. The system can further include a first filler and a second filler, arranged to be mounted over the mold for introducing the filling material and the exothermic mixture, respectively.