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Over the past decade, many industrial builders have turned to using synthetic fiber mesh to reinforce concrete slabs to reduce surface cracks. At the same time, many builders have completely abandoned traditional welded mesh (WWM).
This may seem surprising, because the beauty of fiber optics is that it saves time and money. Using it, builders do not have to pay extra for concrete mesh, and concrete contractors do not have to spend time installing it correctly; in fact, some concrete contractors offer discounts on fiber mesh.
Although the fiber reduces surface cracks, it does not completely eliminate them. Even worse, the lack of WWM can become a real weakness when cracks appear.
This is due to the fact that a properly installed WWM prevents further delamination of the concrete on both sides of the crack and keeps them in the same plane, i.e. prevents uneven settlement. There will be no fiber mesh.
The correction of the differential calculation did not make much impression on buyers. You should sand both sides of the crack, fill the gap with epoxy and try to smooth it all out (see below). Even when done correctly, visible scars remain.
While most of these scars are cosmetic, clients scream for “bad work” and at least many question the structural integrity of the home’s slab. Of course, the developer has to pay for repairs.
As Internet use grows, we see more and more of these problems in the workplace… but we also see more and more construction workers taking notice. Shortly after switching to fiber mesh, one of our customers found about a dozen boards cracking and sagging at any given time. They re-introduced WWM and the problem is almost gone.
The potential for differential settlement is largely dependent on the underlying soil. In places where the soil is sandy and stable, such as Florida, settling is less likely, and using only fiber may be a reasonable option.
However, in areas with clay and other extensive soils, such as the Carolinas, the elimination of problems caused by eliminating the WWM may outweigh the initial cost savings from using the network in the long run.
In fact, the best way to reduce the possibility of cracking and shrinkage is to use the network and WWM on the same board.
Like any structural product, WWM cannot do its job if it is not properly installed. Unfortunately, this is not always the case.
Proper installation for maximum strength requires that the mesh be raised off the ground so that when the concrete sets, it is in the lower third of the slab depth. This means placing wires on the chair to keep it at the correct height (see below).
Wires that weren’t placed in the chairs wouldn’t have been effective, but in the rush to get the job done, some crews removed the chairs and wound the wires right onto the plastic covering covering the dirt. When installers use the chair, they must be careful not to knock the wires off the chair during tipping. If they do, then they need to reset the specific screen.
Ensuring this is all done right can be a learning and quality assurance challenge for builders, and avoiding this problem may be one of the reasons many choose synthetic fibers for these applications.
Richard Baker works as a Building Performance Manager on the IBACOS PERFORM Builder Solutions team to improve the quality and performance of residential buildings.
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Post time: Jul-23-2023