This project shows you how to finish the short edges of drywall that are not tapered and form a butt joint.
The long edges of drywall sheets are tapered. Two tapered edges together form a depression, which makes it possible to create a flat mud joint. The short edges of drywall sheets are not tapered; they meet at a butt joint.
Butt joints are more challenging to finish because they require that you build a slight, gradual mound to hide the joint. To make the mound subtle enough to go unnoticed, you must feather the joint compound over a wide area.
The same fiberglass mesh tape and similar techniques for applying mud are used for butt joints and tapered edges.