I live in an old apartment, circa 1960, my walls are plaster and the building construction is concrete and steel. The original closets are ceiling to floor. I'm looking to change the door to 6'6" door. To do this I need to install a header and cover it with sheet rock. My problem, how should I fill the gap joining plaster to sheet rock
Tape the joints, I prefer mesh tape, then cover joints and skim coat with drywall compound. Once sanded primed/painted, the difference should be invisible. Or...install the drywall backwards(or use blueboard, and skim coat with plaster. But you still have to tape the joints.