Slabs on grade, also called floors on ground, are different from other structural members. First, they are supported directly by soil, and their success or failure may depend more on the soil ...

Also, levelness tolerances do not apply to unshored slabs-on-metal-deck construction. The higher cost of producing high- F-number floors at an age of 72 hours doesn’t make much sense anyway.

The condition and preparation of the sub-grade is important. If there is ground settlement or frost heaving due to lack of water drainage under slabs, the resulting concrete stresses can cause cracks.