The same procedure works on edges around outside corners that are too uneven to.
Are big gaps in drywall sheets a problem.
Larger than that i would fill with easy sand 20 in a mud pan.
Leaving a big gap just isn t a concern.
Huge gaps underneath running the length of each seem in all four corners of the room.
Put a nice coat of mud under the joint tape squeeze it into the joint then put another coat over the top of the tape and feather it out.
Fresh drywall installations include gaps between sheets for expansion as well.
It looks like the drywall was cut too short in some places the gap is 1 wide and the previous homeowners and or contractor attempted to fill the gaps with mud but it didn t work.
Filling large gaps in sheetrock gaps 1 8 to 1 4 i usually mesh tape then paper tape.
The gaps in the joints are even worse where the wall meets the ceiling.
Just fill em up before you get to work taping.
If you have smaller gaps in butts and flats mesh 1st then paper tape.
The mud will adhere to the drywall fill the joint holding the sheets together and the tape will be embedded inside the coat of mud strengthening the whole joint.
Once dry shave it and your good to go.