I’m attempting to upgrade an old two prong outlet to GFCI, and all was going well until one of the outlet boxes turned out to not be secured to a stud or anything. As best as I can tell, it looks like they screwed everything into place, shoved it into the hole in the ball, and then slapped a bunch of plaster over the tabs of the outlet and the box to hold it in place.
So I scraped the plaster off the screws holding the outlet in place to remove it, removed the old two-pronged outlet, hooked up the wires onto the GFCI outlet, and then attempted to shove the outlet back in the box. However, when I did that, the remaining plaster holding it in place broke free, and now it’s just floating free and held in place by nothing. There’s no stud on either side of the box to screw into. What’s my best option here to secure this old box?