Long story short, the wife is pregnant and wants the cats litter box 'outside.' My solution: put a 1'x1' hole in the wall ~10" deep between our living room and patio. Place a pet door over the interior hole. The inside of the wall needed to be enclosed so I put a frame inside the wall using 2x6. I sprayed that expanding insulation foam called Great Stuff all over inside. Let it dry, cut it to the shape of the hole. Sanded and applied joint compound. After it dried the insulation is of course soft so now the joint compound is cracking. I didn't use mesh tape. Since its in the wall it doesn't need to be pretty but it needs to be sturdy and uniform so the cat isn't digging out pits of wall. Is there something I can just lay over the cracking joint compound? Concrete patch ( or would I run into the same problem) or more mud?
I would like to avoid having to rip out the foam and mud I've already spent two days applying.
This has to be the dumbest thing I've ever done, please help!