Concrete Floors: Flatness vs. smoothness

The above image shows rain damage to a slab. Photo courtesy DIALOG

Incorporating floor topping into the specification
The different types of toppings for specific installation requirements can be recommended by a number of manufacturers of cementitious and non-cementitious products. The goal for the specifier is to identify a range of products that capture any compatibility issues inherent between toppings and the substrates that they are applied to, and the finishing materials placed over them. Trusting product representatives and using them as intelligent resources is important; this way, the specifier can focus on co-ordinating the construction documentation.

MasterFormat has a placeholder at Section 09 05 61–Common Work Results for Flooring Preparation. The specification starts by indicating the expected floor flatness as either FF20 or FF25. Keeping in mind concrete floors will continue to change shape between the time of placement and the time of finishing, there needs to be a mechanism that allows for changed site conditions, either by cash allowance or unit price adjustment.

Having money put to one side can greatly improve the co-ordination between the structural tolerance and the esthetic or practical tolerances. One could specify a fixed price to bring the floors from the initial structural requirement of FF25 to the functional requirement of FF50, and use the cash allowance or unit prices to adjust if the actual conditions encountered are different than those expected.

Putting the responsibility for improved floor smoothness and evenness to the flooring installers takes a lot of the guesswork out of the equation with regards to the end result required for the project, and places contract risk for this component into the scope of those best able to address and correct the work. Multiple Work Results in Division 09 can make reference to the Common Work Results specification, meaning each flooring installer has control over his or her own work and is in a more responsible position for co-ordinating the ‘gap conditions’ where different works abut one another.

This is a new approach to an old idea. Change is necessary, but in this case a return to the way things used to be done is an improvement to the entirety of concrete flooring community.

Prez_LRKeith Robinson, FCSC, RSW, LEED AP, has worked as a specifications writer since 1981, and is currently an associate at DIALOG in Edmonton. The immediate past-president of Construction Specifications Canada’s (CSC’s) executive council, he sits on several standards review committees for ASTM and the National Fire Protection Association (NFPA). Robinson is also a contributor to the Terrazzo, Tile. and Marble Association of Canada’s TTMAC Specification Guide 09 30 00 Tile Installation Manual and works closely with the Concrete Floor Contractors Association (CFCA) to address specification requirements for floor flatness and levelness. He can be reached at

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