How To Fill Holes In Metal With Welding. To fix a stripped hole in metal to fix a hole that is too big weld in hole repair kit to bond metal without welding 3 easy ways to fill rust holes in metal. Epoxy is applied until the real hole is repaired or filled.
Also as Brian suggested the weld can be planished to relieve shrinkage with a heavy dollyanvil and medium-weight hammer. However I have discovered a much easier method for doing this. Weld in circles as suggested aiming the arc to the edge of the steel closest to the backer pausing to cool every circle or two and be prepared to grind and fill the backside as it wont be uniform or smooth.
Epoxy covers the whole process from the front side working.
And with Mig welding you risk blowing out more metal than you fill plus the weld can be as hard as a rock. Filling the Entire Hole. In this process rust or paint removed from the surface of base metal. Allow the epoxy to harden.