I'm working to refinish a room and found that the wall underneath a window juts out, likely from a new window installation by the previous owner. I want to make it smooth before painting; what’s the best way to go about it? I was thinking drywall mud to feather out the difference along the height of the wall. But I wonder if there is a easier or better way to go about it?
Is that tape bulging due to settling or water damage? Press on it and slide your fingers over it. Does it depress or make a hollow "shhh" sound? If so, you'll need to cut it away and re-tape.
If not, a wide skim is what's in order. You don't need to go full-height, though. Unless you want to improve the smoothness throughout, just go 12-16" out from the ridge. Use at least a 12" knife.
Apply mud and use a low angle and high pressure. You should basically see the mud scraped clean at the ridge, and the adjacent depression filled to the width of the knife. Leave as little mud on the wall as possible. The only sanding will be a very light surface prep. If done properly, no shaping happens while sanding.