We just moved into a ranch house that's well over 100 years. Unfortunately our family made some unusual improvements to it while the last five generations were living there (during various decades).
In the master bedroom it was decided that there was more than enough room to add a bathroom WITHIN the footprint of the master bedroom. They accomplished this by basically framing-out a closet with wood studs and using plywood instead of drywall.
HERE'S THE PROBLEM: I just removed the huge medicine cabinet/mirror/outlet-strip/built-in-vanity-light so I can install a modern mirror and light fixture. Underneath it, I discovered an unwanted surprise. It appears they had used a saw of some sort to cut a huge 6" hexagonal hole on the far left side of the plywood wall, then the exposed wires had been run out of this hole and spanned about 12" behind the "mirror" to it's hard-wiring source at the top.
So now I have a giant hole to patch/fill in a plywood wall that I can't replace.
The hole isn't going to be hidden by the new mirror and is too weird of a spot to hang a picture.
How can I patch this hole? It's going to be painted but I was told that spackle won't stick to the plywood and will crack when it dries. Plus it's way too big a hole to simply spackle.