Q.: When we saw contraction joints for slabs placed when walls are already in place, we have to end the cut 2 to 4 inches from each wall, depending on the saw-blade diameter. The crack that forms at the end--as a continuation of the cut--is never straight. Is there any way to saw joints all the way to a wall?
A.: We're not aware of any concrete saws that can cut full-depth all the way to the slab perimeter when a wall is already in place. A chain saw permits plunge cuts very close to the wall, but the cut would be wider than the joint and the depth would be hard to control. A handheld grooving tool used during finishing or plastic crack-forming strips that are embedded in the fresh concrete are the only ways we can think of to form joints all the way from wall to wall in one operation.
The short crack at the end of the joint doesn't reduce load transfer, and although the crack width is too narrow to be filled with a joint filler, it's unlikely that hard-wheeled traffic will spall the edges of the crack because forklifts can't get that close to the wall. Thus the cracking problem is primarily cosmetic and isn't likely to affect the performance of an industrial or commercial floor.
For decorative concrete surfaces, a 2- to 4-inch-long crack may be objectionable to the owner. Senior editor Joe Nasvik, a former decorative concrete contractor, says that he would approach the wall as close as possible with a circular saw and then use a handheld grinder with a 4-inch-diameter diamond blade to extend the cut to within about an inch of the wall. Alternatively, he would use a hand chisel to lightly cut the first few inches of the joint in fresh concrete near the wall and then align the sawcut with the chiseled cut.