On Dec 18, 12:39*pm, Tomas wrote:
I recently added some greenboard that butts up to existing drywall.
The existing drywall has semi-gloss paint on it. How do I prep this?
Light sand? I don't want the mudd to start lifting or cracking.

This may spark some outrage, but I saw an oldtimer do this: he cut
about a 4' piece of scrap drywall about 8" wide and cemented it to the
back of the sheet already in place with mud. After everything had set
up well, he tapered the butt edge 6" or so just to the gypsum on the
butt edge. Did the same thing to new sheet butt edge. Mud was applied
to reinforcing patch on the back and the new sheet installed. Next
came tape and mud and the usual finishing. The result was a dead flat
joint, and the reason given was that it was critically close to the
lighting, and would look bad, conventionally done. Extra labor a half
hour. Appearance some years later, perfect.
Only downside is a little more dust than usual from the disc sander.
I'm adding this to my problem solving tricks list.

Joe