Here’s a visual how-to for taping drywall joints.
I have a problem: while repairing several settling cracks, I discovered that one vertical joint above a window had a 3/8″ gap between the edges of the sheets (this is on furring strips on an exterior brick wall). They’d wedged in a sliver of sheetrock and slathered mud over it, with no tape.
I’m going to use mesh repair tape; should I first fill the void between the sheets, or leave it open?
You may want to fill the gap with some blown-in insulation first and then cover with the mesh repair tape and mud.