Butt joint edges refer to the end cut edge on a sheet of drywall that comes from the factory where they cut the drywall into 8’, 10’ or longer sections. When installed on the wall or ceiling, these drywall butt joint edges are put, or “butted”, together as drywall is installed.
While the other sides of the drywall sheet has manufactured rounded edges. These are also put together during the installation but these joints have a recessed seam instead of the flat seam that you get with the butt joint edge.
You can also have a butt edge when you are cutting out a patch and replacing it with a piece of drywall that you cut to the size of your patch.
These cut drywall butt joint edges make it harder to have a smooth patch over the seam because you have to patch over a flat seam or one that may have a raised edge because of the cutting process.
Butt joint drywall finishing can be improved if, after you have secured the butt edges together, take the blunt end of your 5 in 1 tool, or drywall knife or any thing that has a flat edge and run it over the butt seams pushing them down and hopefully flat. This will allow you to have a smoother surface to seam your butt joint edges together.
If the edge still sticks up, take your drywall knife and cut, at a 45 degree angle, along the butt joint edge. Do this to both sides of the butt seam if necessary. This is also good to do on the edge of patches you have cut out as they often have a raised edge from the cut. This will leave a "V" shape going down your seam or any bad part of the seam which you could not get to flatten down.
These will fill when you mud, tape and skim these joints out. This will make your wall more even and allow a flatter skim coat and final finish