Weldable Primer

A weld primer is a thin protective layer that you apply to bare sheet metal to keep it from tarnishing or rusting until welding. The zinc or iron dust in it prevents rust, and the layer makes the weld seam cleaner and reduces spatter. If the layer is too thick or the primer isn't fully dry, it burns off during welding and you get pores in the seam. So apply it thin and even, let it dry thoroughly, and then weld over it – that usually holds well.