We were painting our ceilings and removed the register for the central heating system.
The hole is roughly cut. And I can see right through to the attic along the edges between the duct and the ceiling.
We have a 1939 house and most likely there is lead within the various layers in the ceiling exposed by the hole that was cut.
Also, our attic is really dusty and I don't want any dust to potentially be blown into the room.
I want to seal the raw edges of the ceiling AND I want to fill the gaps between the duct and the ceiling.
How would I go about doing this?
I took Dan D.'s advice and sealed with joint compound and followed up with UL181 metal tape.
What I'll probably also do is to go into the attic and seal around the attic floor/rigid duct interface with caulk or expanding foam.