- Industrial floors home
- Materials, site preparation and placing environment
- Design & construction of commercial/industrial floors
- Floor flatness and joints
- Related Information:
- Commercial Concrete: Information about concrete used in retail stores, restaurants, offices, and more
- Retail Floors
- Subgrades and subbases for concrete slabs
- Jointless slabs: How to reduce or eliminate the number of joints
Floor Flatness and JointsUnderstanding F-number requirements and jointing for commercial and industrial floors
Floor Flatness & LevelnessOne of the things that distinguishes a high tolerance floor is its F-number requirement. F-numbers were developed in the 1980s to provide a systematic, quantitative way to indicate the flatness and levelness of a concrete floor. The higher the F-number, the flatter or more level the floor. There are actually three F-numbers that are used for concrete floors, depending on whether the floor will have a random traffic pattern or defined traffic aisles.
F-min is measured using a traveling profileograph, which simulates the wheel pattern of a high-mast lift truck. Allflat Consulting
FF and FL are measured using either the Dipstick from Face Construction Technologies or the F-meter from Allen Face & Company. The Dipstick was the original device used to measure these values and is stepped across the floor. The F-meter rolls along a defined line.
Joints in Commercial FloorsThe most common types of joints used in commercial or industrial floors are isolation, contraction, and construction. Contraction joints (saw cuts) are the most important. (Learn more about joints.) Properly spaced contraction joints reduce (or eliminate) cracking and help to minimize curling. In commercial or industrial floors, joints tend to create problems since the edges can get broken off or degraded as heavy fork lift traffic crosses the joints. Minimizing or eliminating these joints is often the best solution. It is the responsibility of the designer to specify the location of these joints-if not defined, prior to construction, the contractor should submit a plan for the layout and placement of these joints.
Joints in commercial or industrial floors are virtually always produced by saw-cuts. Ideally, early-entry saws are frequently used to create these joints. This technology allows the contractor to cut the joint sooner both increasing the speed of the project and preventing random cracks from having a chance to start.
Commercial or industrial floors often have heavier floor loads than residential floors. In those cases, we need to have a way to transfer the shear loads across the joints to prevent joint breakdown. As a heavy vehicle approaches a joint, the slab will deflect slightly. Remember that even concrete bends slightly. As it deflects next to a joint, the top edge will crush against the concrete on the other side of the joint. This will eventually degrade the joints. To prevent this, the two sides of the joint are tied together vertically so that one side can't deflect independently.
For years, designers relied on what's called aggregate interlock-the jagged aggregate on either side of the cracked joint-to transfer shear (vertical) forces across the joint. The trouble is that once the joint has opened even minutely due to shrinkage the aggregate doesn't interlock enough to serve the purpose. That's when shear-transfer devices come in handy. The most effective of these are the diamond-shaped plates that transfer load while allowing the slab to shrink both away from the joint and laterally. Learn more about load transfer.
The edges of joints in areas that get heavy traffic need to be supported to prevent them from being broken off on the adjacent slab section. In those cases, we install a rigid joint filler-two-component semi-rigid epoxy resins and polyureas are most common. This rigid joint filler (not a joint sealer, which would be flexible) supports the top corner of the slab. Slabs continue to shrink for years, though, so the slab will often pull back from the joint so that fillers may need to be reinstalled.