Why Concrete Slabs Need Welded Mesh Wire?
Many production builders have switched to synthetic fiber mesh wire reinforcing for concrete slabs in the last decade to decrease surface cracking. Many of these builders have completely abandoned standard welded wire mesh in the process (WWM).
However, while fiber mesh has benefits, it also has downsides that could be costly.
That may seem surprising, given that fiber’s main selling point is its ability to save time and money. Builders do not have to pay a premium for concrete wire mesh, and concrete contractors don’t have to spend time installing it properly; in fact, some concrete contractors provide a discount for fiber mesh.
While fiber reduces surface cracking, it does not entirely remove cracks. Worse, if a break does form, the lack of WWM can be a serious flaw.
That’s because adequately fitted WWM prevents differential settling by keeping the concrete on both sides of a fracture from further separating and keeping them on the same plane. Fiber mesh wire isn’t going to work.
Homebuyers aren’t particularly impressed by repairs to differential settling. You must grind down both sides of the fracture, fill the space with epoxy, and try to smooth everything out (see below). It causes a visible scar even when done nicely.
While such scars are primarily ornamental, they scream “bad craftsmanship” to customers, prompting many to question the structural stability of the home’s slab, at the very least. Of course, the builder is responsible for the repair.
As the use of fiber mesh wire has increased, we’ve witnessed an increase in these issues on job sites. However, more builders are taking note. Soon after converting to fiber mesh, one of our clients observed a dozen cracked and sinking slabs at any given time. They reintroduced WWM, and the problems virtually disappeared.
The underlying soil mainly determines the likelihood of differential settling. When the soil is sandy and stable, as it is in much of Florida, settling is less of a concern, and fiber alone can be a viable option.
Correction of difficulties caused by the deletion of WWM in locations with clay and other expansive soils, such as the Carolinas, can cost more in the long term than the initial cost savings associated with fiber mesh.
Using fiber mesh with WWM in the same slab is the most excellent strategy to reduce the risk of cracking and settling. WWM, like any other structural product, won’t work unless it’s installed properly. Regrettably, this isn’t always the case.
Should raise the mesh above the ground for proper installation and optimal strength, such that when the concrete sets, it is in the lower third of the slab depth. It entails securing the wire to chairs to keep it at the proper height.
The wire that isn’t laid on chairs is ineffective, but some crews skip the chairs and roll the wire directly over the dirt-covering plastic sheeting in the drive to finish jobs. Installers must be careful not to knock the wire off the chairs during the pour when using chairs. If this is the case, the concrete wire mesh should get adjusted.
Ensuring that everything is done correctly can be a training and quality assurance problem for the builder, which may be one of the reasons why so many people choose synthetic fiber for these applications.
However, this type of control must be a top concern in soils where settling is likely.