Abstract: A method for electroslag welding of railroad rails under field conditions employs a special mold bottom member and a special guide tube structure. The mold bottom member includes a metallic insert which is supported by heat-insulating means, e.g. ceramic material in a cavity in a bottom copper block. The ceramic effectively heat insulates the insert from the copper block so when arcing takes place at the start of the welding, the heat is retained by the insert, which forms part of the weld. The guide tube structure is flared toward the bottom and guides two continuously fed electrodes. The structure includes wing-like members near its bottom end. The bottom of the structure is designed wth sharp corners, so that when arcing takes place some of the guide structure metal melts to form a uniform layer of molten metal, which aids in the melting of flux into a slug bath of uniformly distributed temperature.