In your first installment of "Elements in Good Floor Construction" in the March 1969 issue, it is stated that "the topping should have no structural function" in Class 6 floors. Why should this statement be applicable to toppings installed monolithically or integrally with the base concrete slab or toppings installed separately to the base slab and bonded thereto?
According to the proposed American Concrete Institute's "Recommended Practice for Concrete Floor and Slab Construction," published in August 1968, Class 6 floors should have a topping thickness of 3/4 to 1 1/2 inches on the base course at least 6 inches thick; the topping should not be considered in the structural design of the slab. This is a conservative recommendation, taking no chances with poor workmanship that may result in a deficiency of bond between topping and base. The ACI Building Code 318-63 has this to say in Section 907--Effective Depth of Beam or Slab: (a) The effective depth, d, of a beam or slab shall be taken at the distance from the centroid of its textile reinforcement to its compression face. (b) Any floor finish not placed monolithically with the floor slab shall not be included as part of the structural member. When the top of a monolithic slab is the wearing surface and unusual wear is expected, as in buildings of a warehouse or industrial class, there shall be placed an additional depth of 1/2 inch over that required by the design of the member.