I put in 3/8th sheetrock over an old cracked ceiling; finished my taping and spackling and put on 2 coats of primer (it was the glossy kind, all that we had) and then put on one coat of ceiling paint (flat white) before realizing that I should have done one of the seams a little bit better. I guess I felt rushed, but anyway, I'm hoping to rectify my error by trying to even out this seam, which is simply a bit depressed than the surrounding boards, by using a 6 inch spackle knife to apply another thin coat or two to do a better job.
Is there any specific way to approach this? I would think that once the paint is on, there is something that needs to be done, but I'm not sure. Hopefully, maybe just a little abrasion to roughen up the painted surface so as to have the mud adhere? I wasn't planning to put up additional tape for this last couple of passes with the larger knife and some spackle.
Thanks for any help! Paul