I’ve tried quite a few corner pinning methods to prevent corners of bags from sticking out in the plaster. We keep getting faster and faster, and using fewer, less expensive materials. This latest method uses just one stitch of galvanized wire and is the fastest, easiest, least expensive method I know of.
Cut pointed ends on 3” pieces of 16 gauge galvanized wire. Thinner wire might work, so give it a try. A hammer and metal chisel cuts the wire very quickly and with less effort than the metal cutters we’ve used. (Pro metal workers most likely have contractor grade cutters, but most people don’t have these types of tools, so we focus on simple techniques.)
So here’s how we do it. Fold back the corner of the bag about 1-1/2’, poke the wire through the bag and bend over the ends past each other. That’s all there is to it. If the wire is cut with sharp points then the wire will go right through the bags almost effortlessly.
Note: You could try a stapler, but I’m not convinced it would hold up to the rough tamping and handling. Plus, I’ve had bad luck with staplers jamming. Give it a try and let us know the results.