|
Control Joints in Decorative Concrete
Control joints in concrete are used control cracking that would naturally occur. Read on to find tips on placing and cutting control joints in decorative concrete, including how to incorporate them into your design.
by Stacey Enesey Klemenc
This unwritten law of concrete may as well be written in stone because — try as you might — there's no getting around it. So what's a contractor to do? In short, learn to master the art of placing control joints to encourage concrete to crack where you want it to crack.
According to the Portland Cement Association, control joints — also called contraction joints — should be placed at two times the concrete slab thickness in feet for a maximum aggregate size of less than 3/4 inch.
For example, the PCA maintains, the maximum joint spacing for a 5-inch concrete slab with a 3/4-inch coarse aggregate would be 10 feet. If the maximum coarse aggregate size is greater than 3/4 inch, the spacing could be increased to two-and-a-half times the thickness. This would increase the spacing to 13 feet.
Lee Levig, owner of Concrete Works in the San Francisco area, cites what he says is the American Concrete Institute's "rule of three." If you have a four-inch slab, he explains, you would multiply it by three. "So every 12 feet, you would have to cut a control joint," he says. In his area however, he adds, he uses the "rule of two," where his crews cut a joint every 8 feet for a 4-inch slab. "We're in a real clay soil area, where soil expands 8 percent volume from dry to wet."
After determining how far apart you should place the control joints in the concrete, how deep should you cut them? Well, that all depends on whom you ask. |
