Hello all. The shower wall I have installed (1/2" Wonderboard) wraps around to meet drywall in a non water contact area. How do I join this corner to create a decent seal under my mastic and tile? I'm just worried about steam moisture over time. Just tape anf thinset like cement board joints?

where them wonderboard meets the drywall should not be a problem. just tape and mud the joints. the moisture should not be a problem with adequate ventilation thought a ceiling fan.

Thanks for the advice!

Where taping and mud overlap the the cement board use fibre tape and setting type mud ( sheetrock 90 ) as regular drywall compound does not work well over cement boards.

Regular mud will pin hole and bubble over cement.