DaveC wrote:
Adding a partition wall in a finished room. New wall meets finished wall, so
need to mud & tape the corner.

How do you do this? With latex paint on existing wall, mud won't stick well.
Sanding latex isn't a clean solution, and anyway, using abrasives to get down
to the sheet rock paper risks going through it.

Is this just a matter of patience and lots of sandpaper? Or is there a better
solution?

Suggestions?

Thanks,

Should stick fine. I've never epxperienced taping mud not sticking over
latex paint. In fact on several occasions I've skim coated gloss walls
with taping mud as a base for spray and that worked fine also. Another
way is to lay the tape flat on just the new wall and make it tight,
right up to the old wall. In other words don't make a 90 with the tape.
Just make it tight to the corner. Problem with that is a hairline
crack can occur there due to soem shrinkage and may necessitate a very
thin line of caulking be placed in the 90 prior to painting.