Constructing Commercial/Industrial Floors
Construction of a commercial or industrial floor isn't all that different than a residential slab, there's just more of everything—more time spent leveling the side forms, more time spent straightening and restraightening the surface, more care taken with the curing. Commercial or industrial floors are typically placed in long alternating strips. The old practice of placing in a checkerboard pattern is not recommended. The idea with the checkerboard was that the initially placed squares could shrink and then the infilled parts would be placed, keep the joints tighter, but that proved not to really work since shrinkage takes longer than that.
Setting the side forms and screeding has the greatest impact on floor levelness and getting the surface at the specified elevation. For very level floor requirements, like F-min floors, the side forms will be set then checked with surveyor's instruments and planed to precise elevations.
Strike-off or screeding of commercial or industrial floors is often done with a Laser Screed. This allows the concrete to be placed and leveled without the use of any sort of side forms. All Laser Screeds are manufactured by Somero Enterprises and several sizes are available today. These machines are so precise that for medium flatness requirements, placement with the Laser Screed need only be followed by troweling to achieve the desired surface finish.
For higher tolerance floors (higher F-number requirements), the contractor will follow up the initial strike-off with an 8- to 10-foot wide bullfloat or a highway straightedge. Simply using the wider tools can increase the flatness by 50%. The floor is often restraightened several times prior to and after power floating.
A big development with the floating operation was the pans that are slipped onto the blades of a power trowel. The pans can greatly increase flatness. This step is started after the bleedwater has evaporated and when the concrete is hard enough that footprints will be about ¼-inch deep or less
The final step with commercial or industrial floors is troweling, usually with a power trowel, either a walk-behind or a ride-on trowel. Troweling compacts the surface to provide a dense, hard, smooth surface layer. Subsequent trowel pass should be perpendicular to the previous pass.
All of this, of course, is followed by curing. The importance of curing cannot be over-emphasized. If the slab surface dries out, the concrete will lose strength and develop plastic shrinkage cracks. Learn more about curing.
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