How do I fill this gap? The left side of the picture, that drywall was done by the builder and it's finished. Behind it is a 1/2" OSB and behind the OSB is the 2x4 corner stud. The builder did not finish the wall flush upto the stud so when I finish the corner of the wall (right side of the picture) there is 1/2" gap. How do I fill this in to provide backing for a corner bead? I don't want to rip off the finished wall just to build it up to the corner stud. My first thought was to cut 1/2" OSB and glue it between the gap or maybe just fill it with joint compound, let it dry, then install the corner bead. Any suggestion?