This picture shows the lap arc weld. These white stains
are zinc oxide and are the evidence that this spot has not been cleaned nor
grinded before welding. The slag has not been hammered out after welding
nor any corrosion protection coating has been applied. This weld is a structural
one, joining structural horizontal runner to the structural stud, which is done of lightweight steel profiles (fortunately for all of us it's not often that LG studwork forms the primary structure of a high-rise building). I expect quick corrosion because
the gypsum board wouldl be installed onto its face. The gypsum creates
corrosive environment for ferrous metals.
