Q. What is the correct way to specify welded wire fabric (WWF) as secondary reinforcement in slabs-on-ground?
A: The Florida Building Code has recently been upgraded to incorporate the longstanding recommendation of the Wire Reinforcement Institute (WRI) for correct placement of WWF. Specifically the Florida Building Code, Sub-Section 1909.3 Exception 2 reads "Concrete slabs on ground containing 6 x 6 W1.4 x W1.4 welded wire reinforcement fabric located in the middle to the upper third of the slab. Welded wire reinforcement fabric shall be supported with approved materials or supports at spacing not to exceed 3 feet (914 mm) or in accordance with the manufacturer's recommendations."

The second sentence is new and specifies the correct way to place WWF. This sentence, which has been part of all WRI documents for years, puts an additional cost burden for labor and materials on the contractor, resulting in a mass migration to synthetic fibers as secondary reinforcement in slabs-on-ground in the State of Florida. As we have preached for years, wire mesh cannot work as specified if it is not correctly placed in the concrete cross-section. Having a laborer pull the wire mesh up while standing on it just does not get the job done. Frankly, it has never made sense that something so important to the long-term durability of concrete has been ignored. How can wire mesh perform as secondary reinforcement when it is laying on the subgrade? It seems the placement or more appropriately the misplacement of wire mesh goes hand-in-glove with the fact that the formula used to determine the quantity of wire mesh to be used as secondary reinforcement is an empirical, untested formula.

The switch to synthetic fiber, which is approved by Florida (see Sub-Section 1909.3 Exception 1), is now enhanced by a major cost savings. Although it can be argued the move to synthetic fibers in the State of Florida since the early 90s was driven by the durability benefits and cost/time savings documented before the mesh-chair requirement in the building code.

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