Small and mid-size contractors should be aware of floor flatness concepts and some inexpensive ways to improve flatness. Improved flatness can be a marketing advantage, attracting new and repeat customers and providing opportunities for more work.
FF is the flatness number and FL is the levelness number. Flatness describes wavinessof the floor. Levelness describes variation from a theoretical horizontal plane. Higher numbers indicate flatter or more level floors. F-numbers are linear: a floor with FF30 is twice as flat as one with FF15.
Consider having tests run on other floors placed by your crews before bidding work with F-number specifications. Contractors not currently bidding work with specified flatness requirements may wish to enter this market by experimenting with construction of FF25 / FL20 floors. With some experience in improved floor quality, they can attempt to place and finish even flatter floors. However, a contractor should know how to do the work before bidding on it.
Slab levelness depends on the contractor's accuracy in setting forms and straightness of the vibrating screed or hand straitedge used for strikeoff. For the most part, flatness is affected by finishing operations after strikeoff. Many material and construction factors also affect a contractor's ability to place flat floors.