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Superflat® Concrete

Ff/Fl High Spot Remediation

Floor specifications critical for a particular intended use can be identified, controlled, and met using the F-Number System. Therefore, correctly understanding and implementing this system is the only real way to ensure the desired use can be properly achieved.

Understanding Floor Flatness

The F-Number System is the industry-adopted standard for the specification and measurement of concrete floor flatness and levelness. F-Numbers, as they are called, extend in range from zero to infinity and communicate the way a floor measures—the higher the F-Number, for example, the flatter the floor. This flatness/levelness is notated as Ff for flatness (a measurement representing the bumps or grooves in the floor) and Fl for levelness (a measurement relating to the tilt or pitch of the floor).

Why is this important? With passing time, joints and cracks in a concrete floor will curl, making the floor less flat. Floor flatness and levelness should be measured within 72 hours of placement, but preferably within 24 hours. If that window of time is missed, any Ff/Fl numbers acquired may not accurately represent the flatness of the floor.

Floor flatness (Ff) is written first, such as Ff/Fl. The Ff number represents the flatness of your concrete floor and the Fl number indicates the tilt or pitch of your floor. This levelness indicates how closely your finished floor matches the intended slope as described in the original design documents. To properly measure Ff/Fl, elevation differences need to be measured every 10 feet within a 72-hour timeframe after concrete has been placed. Fl numbers are linear, so an Fl of 50 represents a floor that is twice as level as a floor measuring an Fl of 25. Taking into consideration the amplitude and wavelength of a particular floor, Ff numbers illustrate how close to planar the floor actually is; it is a statistical representation of the waviness or bumpiness of a floor. Changes in elevation are measured every foot within 72 hours of the concrete being placed, and use of a standardized formula determines the resulting Ff measurement. As is the case with Fl, Ff measurements are linear—the higher the number, the flatter the floor. For example, a floor with an Ff measurement of 80 is twice as flat as a floor with an Ff of 40. Ff numbers can be attained on slabs on grade as well as elevated slabs. The floor flatness is critical for spaces where equipment needs to be set perfectly level—or for any intended use that requires a floor to be flatter than a typical concrete slab.  

When we refer to floor levelness (Fl), we are generally referring to slabs on grade. These particular slabs are often designed with camber, which later becomes a concern when support staging is removed, as the result is typically a sagging floor. Fl is only specified on an elevated slab in situations where measurements have been taken in the beginning—before shores and forms are removed—and so long as the slab contains no camber. When a slab has camber, the structural slab must be placed first (and allowed to deflect to its final shape) and followed with a topping finish slab that then gets measured. At this point, the resulting floor levelness (Fl) measurement—which measures the elevation difference along a sample line at 10-foot intervals—communicates the separation of the floor from the original slope or plane.

Flatness Classifications & Benefits

Ff/Fl numbers have the following floor flatness classifications:




Ff 45/ Fl 35 – FLAT


Ff 60/ Fl 40 – VERY FLAT


Ff 80/ Fl 60 – SUPER FLAT

It can be very useful for architects and owners to visualize the defects represented by Ff numbers. Many were/are accustomed to the straightedge method, which consisted of measuring the greatest defect along a 10-foot straightedge. These values provide a general estimate of defect level with correlation to Ff number:


Ff 25 will have a single 1/4" defect across 10 feet


Ff 50 will have a single 1/8" defect across 10 feet


Ff 100 will have a single 1/16" defect across 10 feet

One thing to understand is that just because a specified floor was signed off on and paid for doesn’t always mean it measures as flat as it is supposed to. The only way to be sure is to properly measure floor tolerances using state-of-the-art equipment.

With the rapid advancement in machinery, robotics, and complex logistical systems, superflat floors have become critical for successful and efficient operations. Achieving a superflat floor can determine what kind of racks and logistics systems will be utilized during operation and will make it possible to acquire the most advanced of those systems. It will also impact the amount of maintenance required on existing equipment and eliminate unnecessary spend on repairs. It provides new opportunities for industrial plant and facility owners to implement modern robotics and rapid picking systems, knowing they have the right floor to sustain those advancements. A superflat floor also:


Impacts how fast fork trucks, robotics, and other equipment can move around the facility.


Minimizes risk of rack impacts and handling errors.


Improves overall operational safety.


Allows for taller storage systems and, potentially, tighter aisles.


Creates faster, more efficient operations and maximizes profitability.

Do I have defined traffic floors or random?

When we begin to talk about very narrow aisles (VNA), we use a different identifier to represent superflat floor specifications—known as the ACI F-min numbering system. This system refers only to defined traffic floors. Ff/Fl and F-min are altogether different measuring systems. There is no direct correlation between the two, and therefore no corresponding index for comparison. Ff100/Fl50 is used to reference perfect flatness for random traffic floors. You can learn more about our remedies for VNA floors here.

Here are some common questions we receive at Superflat® Concrete regarding superflat floors:

What methods does Superflat® employ to attain perfect flatness?

Superflat® offers various services depending on the project’s degree of development. For projects in the first stages of construction, Superflat® measures the site and outfits the client with a custom logistics plan to ensure that the construction starts off on a level foot. For projects that have already been built out, Superflat® measures floor flatness and floor levelness (Ff/Fl) to determine the extent of remediation. Remediation comprises milling and grinding of the substrate until the ideal texture for proper flatness is attained.

How does a Superflat® floor make your business more efficient?

A perfectly level concrete floor is not to be underestimated. In defined-traffic facilities such as distribution centers, flat flooring provides a smoother surface for warehouse vehicles like forklifts and scissor lifts. The smoother surface mitigates the potential for vehicle-related setbacks like spills or collisions while allowing for quicker transport, translating to the product getting out the door sooner rather than later.

Additionally, investing in flat floors from the beginning results in less time spent fixing issues down the road. Say you want to install tiling or any other secondary flooring in your facility. A contractor working with an uneven floor will have to spend hours correcting inconsistencies just to get to square one: a level surface. Time is money and these extra contractor hours will result in unnecessary expenses for your business. Let Superflat® start you off on square one.

How do Superflat® floors promote safety in the workplace?

A level floor is a safe floor. In bustling warehouses and distribution centers, an uneven patch of flooring can easily be overlooked. It only takes seconds for an employee to trip and fall or a top-heavy piece of transportation equipment to lose its footing and topple over. Accidents like these happen every day and result not only in expensive repairs and/or loss of product but also potential employee injury. An even floor is not a luxury—it is an essential feature in any facility that values the safety of its employees.

Why is a Superflat® floor a worthwhile investment?

Many people consider flooring an afterthought in the construction process. Afterall, a floor is just something you walk on, right? Wrong. It is becoming increasingly common for floor levelness to be tested during routine construction inspections. A floor is literally the base upon which your business is built. A level floor creates efficiencies in both time and money, not to mention a safer workplace environment. Your business deserves a Superflat® foundation.