"Bill" wroteI purchased a 25# bag of Durabond 90 today.

1. Can I mix it in a plastic bucket (package says it gets "very hot")?

Yes. It gets warm, but nowhere near that hot. Kinda like quick epoxy
kicking off.

2. If I apply it with tape, would I generally add more tape if I add
setting compound later?

No. If you cover it with regular joint compound, scrape all off to get it
flush with the surface, then let it set and tape and finish it like a normal
new joint.

The dust warning is just to keep you from inhaling it and getting your lungs
messed up like miner's lung. Breathing rock dust is generally considered to
be a "bad thing" (TM) g
--
Jim in NC