is a 4″ concrete slab actually only 3.5″ and if so, what is its implication for a garage floor?

I asked my concrete guy for a 4″ slab for my garage and woke up last night in a panic with the feeling that the expansion joint material I saw… I asked my concrete guy for a 4″ slab for my garage and woke up last night in a panic with the feeling that the expansion joint material I saw…Read MoreGreenBuildingAdvisor