Straighten a Twisted Outside Corner Without Carpentry

Carpenters added a new closet to this room, tying the new framing and drywall into the existing short wall.

I had just started the taping when I noticed the bad twist at the ceiling line.

Compared to the new, the old wall now looks worse than it did before.

The plastic-lined drywall scrap is fastened from the adjacent side (with screws for easy removal), and serves as a mudding jig.

With this guide in place, this outside corner can now be built out square and flush with mud from the ceiling down several feet.

Plastic stops the mud from bonding to the scrap drywall guide.