As a licensed concrete and brick mason in the City of Chicago, I’m often asked what the difference is between fiber mesh and WWF (welded wire fabric) when giving estimates. My first response to home owners is “Turn and RUN from any contractor who tells you ALL you need is fiber mesh because it’s stronger than WWF”.
So what is fiber mesh and what’s it for? Fiber mesh is an additive of synthetic fibers usually added at the mixing plant. The fibers are used to solve a very particular problem called shrinkage cracking. In the first few days of freshly poured slab life, the water in the initial mixing is evaporating from the concrete and it’s actually shrinking ever so slightly. The problem is that concrete does not shrink evenly as a whole, think of it more like a pie cut into four or more pieces. The concrete is shrinking away from each individual cut and in on itself. This is why we put in control joints (the lines in you see either tooled or cut into the concrete) to help dictate where the concrete will crack.
The fiber mesh’s job is to help hold the concrete together in that initial drying phase only, and when it cures, does little to NOTHING to add to the strength of the concrete. So why use is it that contractors will steer you towards substituting fiber mesh for WWF, because the contractor either is pulling the wool over the customers eyes or doesn’t know any better themselves. It sounds good, like a high tech answer to an age old problem, but it isn’t.
So what does the WWF do? That is another good question, and the answer depends on where the contractor places the WWF during the pour. If the WWF is lying on the ground and is never lifted into the pour, it then is not very effective. If it is lifted and suspended in the concrete, it then serves two purposes. First, when it does crack and it WILL CRACK (any contractor who says the other is someone to stay clear of) the WWF helps keep the two now separated cracks from spreading apart from one another. The second thing WWF does is to keep two sections of concrete that are divided by a crack in the same plane (meaning that one won’t sink while the other sticks up). These two attributes along with properly placed control joints will help give your new concrete a chance at long life.
Please feel free leave any comments or use the Contact Us tab and ask any other questions that you may have.