I have to make a repair to a plastered ceiling where the stairwell ceiling meets the lower hall ceiling and was wondering if anyone knew of an extra hard plaster or compound I could use. I'm concerned that regular compound will chip off the soft corner where the two ceilings meet.

I used LePages powder that is mixed with water for my ceiling repairs and it worked.

Tick

Use a corner bead and repair with drywall joint compound.

Use a drywall corner bead and use durabond 90 the brown bag not the easy sand 90