I friggin’ hate drywall. But when you like in paper mache houses like we have in the US, you have to deal with it. I can’t tell you how many crappy patches I’ve had to do in the past (when we moved into this house there were so many holes punched in doors and walls from the previous owner!) I especially hate large holes in drywall because there never seemed to be a good way to plug them without some kind of support from inside the wall. Then I found this method on some random video and have been using it ever since.
The first step is to standardize the hole. This sounds dumb, but you have to cut a slightly bigger hole in the wall. The trick is to make your hole a simple shape with straight sides. Triangles and rectangles work well for this.
The next step it to get some patch material. You can get a 2” x 2” piece of drywall form any big box hardware store. Measure the hole you cut in the wall and cut out a piece that is a couple inches bigger on each edge. ie. a 5”x 5” hole should get a patch that is 9” x 9”.
Here’s the trick! Cut the outside dimension completely through, but only score the actual hole size lines on your patch.
Then remove the edge pieces being careful not to tear off the facing paper.
Test fit this patch to see that it fits your square hole.
Remove the patch and liberally apply mud to the edges of the hole and the edges of the patch. You will need mud on both of these!
Stick the patch back on the wall and flatten it out with a large putty knife. This may take a couple of cycles of mudding, drying, sanding, and mudding again until it’s all smooth.
When you are done, paint the wall. This was in my garage so there wasn’t a big need to do it, but we had been planning to paint anyway. Painting the garage is the actual reason I needed to patch this in fact.