Sawing Concrete

Continued

Track mounting is the secret to smooth, controlled sawing. The saw's guide track attaches to adjustable mounts that are secured to the wall itself with expansion bolts. The bolts must be offset from the cut line by 8 1/4 inches but, in most cases, they can go inside the cutout area, eliminating the need to patch the holes later. To ensure square, accurate cuts, the track mounts are trued using four adjustable set-screws. We set a torpedo level on top of each mount and tweak the screws until the bubble reads plumb and level, then we attach the track to the mounts and true it up as well (Figure 4).

Figure 4. Track mounts are installed and individually leveled for alignment (top). The mounts have a slotted hole that allows the track to be tapped into level after attachment (above). Four adjusting screws in each mount allow the track to be leveled or squared to the cut (inset).

Although setup takes nearly as long as the actual cut, it's time well spent, because the smooth, clean accuracy of a wall saw's cut is unmatched by other methods. An average door opening — two vertical cuts through the wall — takes from four to five hours to complete, including travel, setup, and breakdown time. We use an ordinary socket wrench to hand-crank the saw along the track while sawing, but a remote attachment is also available that allows the operator to control the saw's operation from several feet away. Remote operation adds a margin of safety and keeps the operator drier.

Dust Control

Because the cut is continuously flushed with water from a garden hose connected to the saw, there is no free-floating dust. The damp, gritty mist that results instead is easily contained by a temporary plastic curtain. A bigger problem is the puddle of water and slurry that forms at the base of each cut. If we're working in a finished interior space, someone has to stand by with a wet-vac to suck up the runoff during the cut.

The automotive transmission fluid that's ordinarily used to lubricate the impeller blades of the pneumatic motor blows off and spatters the wall alongside the cut (Figure 5). In the case of a finished interior, this might be objectionable, so sometimes we omit the lube. The impellers will wear out earlier as a result, but they're fairly inexpensive and easy to replace.

Figure 5. Impeller lube and concrete slurry stain the wall after sawing. The lube (automotive transmission fluid) can be omitted to reduce cleanup when altering a finished interior wall.

Hand Tools

A circular blade has its shortcomings. If we're sawing through a wall and there's a framed floor overhead, we can't make a clean pass through the top of the wall (Figure 6). You could finish the cut by knocking the cutout free with a sledgehammer, but that would leave a damaged "ear" at the corner. Instead, we prefer to score the backside of the cut-line by hand with a 4-inch-diameter electric cutoff tool, then carefully complete the breakthrough with a pneumatic chisel.

A circular blade won’t complete a corner cut without overcutting, either. Whether we’re restricted by aesthetics or a physical obstruction, we have to resort to other tools to complete a cut from one side of the wall.

Figure 6. An overhead floor limits a though-cut (above). To avoid a broken "ear" at the top corner, the author scores the backside of the cut with a hand-held cutoff tool (left) and carefully completes the cut with a pneumatic chisel.