Zinc

Zinc has a significantly lower melting and boiling point than steel. When you hit it with the arc, the zinc layer evaporates instantly. The vapor tears open the weld pool, you get porosity and spatter, and the white smoke is toxic – it gives you zinc fever. Also, zinc can migrate into the steel's grain boundaries and make it brittle. So: grind off the zinc layer at the weld seam beforehand, weld, and then brush the area with zinc spray again. And turn on the fume extraction when welding galvanized material.