I'm looking to convert a screened in porch to an enclosed room, but the slab is below the grade of the house. I'm considering pouring a new slab on top of the existing one. The existing one has cracks but has been stable for the 8 years we've owned the house. Right next to the house the slab sits slightly more than 2" below the foundation of the house (also a slab). Can I pour a slab that thin? One contractor has bid the job but is not guaranteeing against cracking. I'm planning to lay ceramic tile on top of the new slab. If I can do it I was thinking of building permanent forms, hoping that they may serve as control joints and minimize cracking. If I can pour, should the slab float or be tied into the surrounding brick knee wall? And it would seem that a slab of 2-3" thickness would be too thin for mesh.
An alternative that has been suggested is to build a subfloor on top of the existing slab up the the grade of the house foundation, but I'm worried about moisture, bugs, etc. Any suggestions would be appreciated.