An exothermal weld mold includes a mold section with an integral cover portion, made as part of a single piece of material with the rest of the mold section. The mold section may be a mold half of a vertically split mold, or may constitute most of a half of the mold. The cover portion may be part of an integral cover that covers substantially all of a reaction chamber or crucible of the mold. The cover may have one or more vent holes, in the top and/or side of the mold. The cover may have a baffled passage for expansion of gases produced by reaction of the weld material, before the gases are expelled from the mold at an opening in the top or side of the mold. The passage may be a serpentine passage. A filter may be placed in the passage.