To fabricate a butt joint, the joint faces should be preheated sufficiently to promote complete fusion between the Thermit deposit and the base metal. Even though it is called a welding process, Thermit welding resembles metal casting where proper gates and risers are needed to:
1) Compensate for shrinkage during solidification (2) Eliminate typical defects that appear in castings (3) Provide proper flow of the molten steel
(4) Avoid turbulence as the metal flows into the joint