Q.: You published a notice on page 372 of the March issue about an ACI Committee 117 warning to people about specifying floor flatness within 1/8 inch in 10 feet unless needed for special purposes. The committee also warned contractors not to bid on such jobs without taking into account the specialized placing and finishing techniques that are needed to construct them. Why the sudden warning?

A.: The warning is not so sudden. In the past several years the industry has become increasingly aware that specifiers have tended to specify 1/8 inch in 10 feet or something similar without considering whether such a tight tolerance is actually needed. Contractors have bid on such floors and built them. Very seldom have the completed floors been measured to see that they comply with specifications. When the floors have performed satisfactorily with respect to flatness--as they almost always have--the owners, the specifiers and the constructors have almost universally assumed that the floors met the specifications. Much evidence of recent years has shown that this is not so. When it has been discovered that a floor does not meet specifications it has frequently led to unnecessary contractual and legal disputes. Everyone should become more aware of what is really needed and what it may cost.

Warning published in March 1984:

Warning on Floor Tolerences

American Concrete Institute Committee 117, Tolerances, has issued a warning regarding concrete floor tolerances. The warning, published in Concrete International, December 1983, page 6, reads as follows:


In studies of finishing tolerancs of in-place floor slabs conducted by ACI Committee 117, Tolerances, the indication is that the commonly specified floor finish tolerance of 1/8 inch in 10 feet is not being achieved except in special use floors employing highly specialized placement and finishing techniques. Architects, engineers and specifiers are cautioned against using this tolerance except where required for special use such as the drive aisles of high lift fork truck warehouses. Contractors are cautioned that the 1/8 inch-in-10-foot tolerance requires highly specialized placing and finishing techniques.

Industry standard procedures involving high production placing and finishing techniques are producing serviceable floors which do not conform to the 1/8 inch-in-10-feet finish tolerance. Indiscriminate use of this tolerance when not needed may raise the potential of unnecessary contractual and legal disputes.

ACI Committee 117 recommends the use of the finish tolerances contained in "Standard Tolerances for Concrete Construction and Materials (ACI 117-81)," taking into consideration the intended use of the floor and the construction materials used. Committee 117, working in conjunction with Committees 301, 302, and 318, hopes to provide a better defined finish tolerance and measuring techniques in the near future.

Dean E. Stephan Chairman, ACI Committee 117