Is the mold coat really the only thing stopping a fuse? I've seen casts stick even with a good coat when the sand was too damp. @nora_hart95 mentioned the thin layer doing work, but in my experience, the sand quality and moisture play a bigger part. For example, last month we had a fuse because the sand wasn't packed right, not from missing the coat. So skipping the coat is bad, but fixing the sand is just as key.