I have three apartment buildings (with three, four, and five units). Their basements were insulated just over 10 years ago with closed cell spray foam with a class one fire rating. Now for some reason, the building inspector says I have to cover the foamed walls of all three large basements with 0.5 in. (12 mm) drywall and build stud walls to hang the drywall for fire protection. This would reduce the width of the basement stairs significantly, and they would become so narrow that they would then be out of compliance. These basement walls are uneven fieldstone foundations, with bumps, protrusions, and even some curves. I was thinking that shotcrete-applied concrete might work much better and be more appropriate than wood and drywall for a sometimes-moist basement. According to the local Building Code, a 2 in. (50 mm) layer of concrete would suffice. How can a shotcrete application be made to adhere to closed cell foam? The wall heights are approximately 7 ft (2 m) plus bond.