Q: As part of the renovation of an old steel mill, we have to make a large opening in a 31_2-foot-thick concrete wall. The general contractor says that the concrete is too thick to be cut with a wall saw. How can we remove the concrete?
A.: There are two other ways the concrete can be removed: diamond wire sawing or stitch drilling. Diamond wire sawing is feasible only if you have access to the back side of the wall. Otherwise, stitch drilling is the only option.
A diamond wire saw cuts with a steel wire that contains diamond-impregnated steel beads. The wire is threaded through holes drilled at the corners of the area to be removed, and the ends are joined by a steel connection sleeve. This continuous-loop diamond wire is mounted on a flywheel and directed to the cut by a series of idler wheels. The flywheel, driven by a hydraulic or electric motor, propels the wire. The wire loop is spun in the plane of the cut while being drawn through the concrete. The thickness of concrete that can be cut by diamond wire sawing is limited only by the power of the motor. However, you must have access to the back of the wall to loop the wire around the concrete. If you can't reach the back of the wall, stitch drilling is the only option.
Stitch drilling involves drilling overlapping bore holes through the concrete along the perimeter of the area to be removed. Its primary drawback is the risk of costly removal complications if the cutting depth exceeds the accuracy of the drilling equipment, so that uncut concrete remains between adjacent holes. Also, the opening created has very rough edges, so additional concrete removal may be required.
To locate a contractor with diamond wire sawing and stitch drilling capabilities, consider calling the Concrete Sawing & Drilling Association at 614-798-2252 for a list of contractors in your area.
ACI 546-96, Concrete Repair Guide, American Concrete Institute, 1996.