Welding Galvanized Steel

Welding galvanized steel comes with a safety warning that’s not optional. Zinc coating vaporizes at 1665F and produces toxic zinc oxide fumes. Breathing these fumes causes metal fume fever, a condition with flu-like symptoms that hits 4-12 hours after exposure. Every galvanized welding job needs local exhaust ventilation or fume extraction at the source, plus a P100 respirator.

The zinc coating also creates welding problems. Zinc vapor gets trapped in the solidifying puddle and creates porosity. The burning zinc generates heavy white smoke that obscures the puddle. And zinc contamination makes the weld bead rough and inconsistent.

The cleanest approach is grinding the galvanized coating off 1-2 inches back from the joint before welding. This eliminates both the fume hazard and the porosity problem. Weld on bare steel, then cold-galvanize spray the completed joint to restore corrosion protection. This is the standard practice for structural and code work.

When grinding isn’t practical, technique adjustments help. Slow your travel speed slightly to give zinc vapor time to escape before the puddle freezes. Push the MIG gun (forehand technique) instead of pulling, which keeps the arc ahead of the fume plume. Increase stick-out by 1/4 inch to reduce heat input. Running straight CO2 instead of 75/25 mix sometimes helps zinc escape with the more turbulent puddle.

Silicon bronze MIG brazing (ERCuSi-A wire with 100% argon) is the best alternative for sheet gauge galvanized. The wire melts at about 1800F, just barely above zinc’s boiling point, which minimizes zinc burn-off and fume generation. The joint retains most of its galvanized coating, and the bronze bead has natural corrosion resistance.