02
Cut, back, tape and feather so a patch disappears
A hole bigger than a fist gets squared off, and a strip of backing is screwed behind it so the new board has something solid to sit on. Small holes take a mesh patch. Either way the new piece goes in flush with the old surface, never proud of it, because a patch that stands up shows in every raking light.
Joints are taped with mesh for quick work or paper where a seam has to hold, then covered in three thin coats of compound, each one wider than the last and dried before the next. Thin coats are the whole trick. One heavy coat shrinks, cracks and needs so much sanding that the ridges come back.
Sanding is checked with a light held low across the wall, which throws every ridge into shadow. Then the patch is primed, because bare compound drinks paint and shows as a dull square.