Q.: We are bidding a job that has a slab-on-grade gymnasium floor with specified floor flatness of FF 100 / FL 50. Is this reasonable?
A.: It depends on the overall quality of the facility and the nature of the floor finish that will go over the concrete. This specification seems to be rather restrictive for ordinary facilities. We asked several floor contractors and consultants for their experiences and recommendations. They suggested F in the range of 35 to 50, and one thought that FF 35F / FL 25 would be sufficient for most cases. The specifier on this project obviously is serious about obtaining a flat floor, but may not understand the costs. Work with the specifier and a prospective flooring installer to review performance needs. Consider the whole floor system, not just the flatness issue.