The last mustang restoration video, we applied fiberglass filler over the weld location to seal the weld. After sanding the fiberglass, I primed it to prevent rust from occurring on the bare metal until I was able to work on it again.
This video, I sanded the primer off to apply and block sand body filler. Once I have the body filler shaped and smoothed, I can prime the repair area and start on the other quarter panel.