When a drywall seam becomes visible it is quite a lot of work to hide it correctly.
That said, it's totally doable in the usual 3x as much time as you expected.
- Try spackling/sanding the gap. Give up after a few tries because it looks crappy. Learn the hard way that you are gonna have to do this one right.
- Go to home depot. Buy heftier spackle (not the cheap crap you use to fill nail holes.), a wider putty knife, some of that flexible fiberglass tape for this very purpose, and get a belt sander used on ebay or soemthing.
- use the narrow end of the sander (the part where the belt makes a abrupt 180 degree turn.) to rub down a groove that is a couple millimeters deep and the width of the tape.
Note: I don't think this is the correct usage of a belt sander... I don't really care though.
- clean off the wall with a shop towel.
- apply tape
- apply one coat of plaster... don't try to fill in the whole gap. Let it dry ~1hr.
- sand the excess off. Apply another coat. This one shoud be sufficient.
- Sand it smooth by hand or with a less agreesive electric sander.
- go to home depot again, and buy the textured wall in a can. Use that on your smoothly sanded fixed and filled seam. (I had to use the finest texture tube to match my wall. I still had to sand a little of the texture off to get it to match.)
- Paint it. Be happy.
- Vaccum the carpet a zillion times to clean the mess. (this one is a theory, i've only vaccumed once, so it's still a mess.)
Cost? Shit, I dunno... About 3$ spackle knife, 3$ spackle, 5$ fiberglass tape. ~10$ textured paint. (plus tools: 50$ in sanding equipment)
So yes, I thought it would take an hour or two and it ended up taking a few hours on multiple evenings, but it looks... Sooooo Goooood
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