Q.: We're going to be placing a 6-inch-thick concrete slab on grade that requires welded wire fabric for crack control. Plans call for it to be in the center of the slab. We think it ought to be closer to the top. Also, we want to place the concrete in two layers, laying mats of the fabric between them. But the architect says we can't do it that way because we may get a cold joint where the two layers meet. Is he right?
A.: The Wire Reinforcing Institute recommends locating welded wire fabric 2 inches below the surface in a 6-inch-thick slab. They also say that the two-course method is probably the most effective way of placing fabric, although it takes more time. Place the top course before the lower concrete starts to set to avoid producing a cold joint.