How do you cut cast iron drain pipe?

A snap cutter, a saw, or, for big pipe, an abrasive saw. The Cast Iron Soil Pipe Institute (CISPI), the industry's trade group, says in its handbook: "The snap cutter accounts for the majority of all cuts made on cast iron soil pipe in the field." RIDGID's manual describes how they work: "All RIDGID Soil Pipe Cutters use chains equipped with cutter wheels that are tightened around the pipe until the pipe breaks."

For a saw, the blade matters. Ordinary bi-metal blades dull fast on iron. Blade makers sell carbide-tipped blades for it; Milwaukee, for example, says its carbide cast iron blade is made for "the fastest, smoothest cuts in hard cast iron."

RIDGID sets one size limit for its chain cutters: "Do not extend the chain to cut soil pipe greater than 8" in diameter." Bigger pipe goes to an abrasive saw.

Secure it above and below the cut so nothing can move when the pipe separates. This is the part people skip, and it's the part that hurts people. Charlotte Pipe's manual says "Always secure pipe before cutting so that it cannot roll, drop or slip," and warns "Unsecured piping can fall and cause serious injury." RIDGID adds: "Be aware that when the pipe is cut the soil pipe cutter and pipe could drop or fall."

The weight is real. Charlotte's manual lists a 10-foot length of 4-inch no-hub pipe at 76.0 pounds, and a 10-foot length of 3-inch at 54.0. A vertical stack running up through a wall carries the weight of all the pipe above it.

How to support it:

• Vertical stacks. Put a riser clamp on the stack above the cut, resting on the floor framing, and another below. Charlotte says to "Use approved riser clamps, floor clamps, or friction clamps for this purpose." In buildings over two stories, it says to "support the stack at the base and at each floor with an approved clamp." Cutting out a section of a stack with no clamp above leaves the upper pipe hanging on its joints.
• Horizontal runs. Make sure hangers or blocking hold the pipe on both sides of the cut. The plumbing code's Table 308.5 sets cast iron hangers at a maximum of 5 feet apart horizontally, raised to 10 feet "where 10-foot lengths of pipe are installed," and 15 feet vertically.
• Old pipe. Old cast iron can be thin or cracked near the cut. Expect it to break in the wrong place, and have the support in place before you start.

Our page on pipe hanger and support spacing covers the code rules for every material.

Mark, wrap, score, then snap. CISPI's procedure:

1. 1Mark the cut line all the way around the pipe.
2. 2Position the chain. CISPI says to "position the chain cutter squarely around the pipe to assure a straight cut. The maximum number of wheels possible should be in contact with the pipe." RIDGID says: "Make sure that the cutter wheels are square to the pipe."
3. 3Score first. Apply pressure to score the pipe, then rotate the cutter slightly and score again. CISPI says "Scoring the pipe before the actual cut is the key to a clean straight cut."
4. 4Snap. Apply steady pressure until the pipe breaks.
5. 5Clean the end. CISPI says "When installing pipe that has been cut, make sure the sharp edge is removed," because a sharp edge can catch the coupling's gasket. File or tap the edge smooth.

Wear eye protection and gloves. Charlotte says to "Always use protective equipment including eye protection and safety clothing while installing or cutting pipe," and RIDGID warns that "Cutting can cause pieces of pipe to be thrown with considerable force."

### What about cutting with a saw?

Clamp the pipe the same way, mark a square line, and let the blade do the work at a steady speed. Charlotte's rule for any method: "Pipe ends are to be cut as squarely and smoothly as possible." A crooked cut won't seal well inside a coupling. Saw cuts also rattle the pipe, which can loosen old joints nearby, so check them after.

With a no-hub coupling: a rubber sleeve with a stainless steel band around it, clamped over both pipe ends. The code, in Section 705.3.3, says these couplings "shall consist of an elastomeric sealing sleeve and a metallic shield that comply with CISPI 310, ASTM C1277 or ASTM C1540," and that the sleeve "shall be provided with a center stop." The center stop keeps each pipe end seated halfway into the sleeve.

• Cast iron to cast iron. Use a shielded no-hub coupling. Charlotte recommends that "all no-hub pipes be joined with shielded couplings conforming to CISPI 310, ASTM C1277, or ASTM C1540."
• Cast iron to ABS or PVC. This is the common repair: cut out a cracked section and splice in plastic. Section 705.16 says "Joints between different piping materials shall be made with a mechanical joint conforming to ASTM C1173, ASTM C1460 or ASTM C1461." ASTM C1460 covers "shielded transition couplings to join dissimilar DWV pipe and fittings." Plastic and cast iron have different outside diameters, so the coupling has to be made for that pair.

Tighten the bands with a torque wrench, not by feel. Charlotte says "Hubless couplings require 60, 80, or 120 inch-pounds torque wrenches," depending on the coupling, and CISPI's handbook says the bands "should be tightened using a calibrated torque wrench set at 60 in./lbs."

For cast iron to cast iron, the metal shield is part of the code requirement, so a plain rubber sleeve with hose clamps doesn't meet Section 705.3.3.

Lead, and the condition of the pipe. Older cast iron was joined with hub-and-spigot joints packed with oakum and sealed with poured lead; the code still describes the method in Section 705.3.1: "Molten lead shall be poured in one operation to a depth of not less than 1 inch (25 mm)." Cutting through a hub or heating an old joint can release lead. OSHA notes workers "may also be exposed during installation, maintenance, or demolition of lead pipes and fittings." Cut in the straight pipe between hubs rather than through a joint, don't use a torch on old joints, and wash up before eating.

The other issue is what the cut shows. Older Phoenix homes built before builders switched to ABS plastic can have cast iron under the slab, and when you open it up you may find heavy scale or a thin, cracked wall. If the pipe near the cut is rotted through, a short splice won't hold for long. Our page on how long cast iron drain pipe lasts covers the signs, and when builders stopped using cast iron helps you date what you have.

### Should you cut it yourself?

For an exposed horizontal pipe that's well supported, a homeowner with a rented snap cutter can make a clean cut. Call a plumber when:

• The pipe is a vertical stack carrying pipe from upstairs or a roof vent.
• The cut is under a slab or inside a finished wall.
• You find lead joints, or the pipe is cracking in places you didn't cut.
• The repair ties into the main building drain, where a failed coupling means sewage under the house.

Replacing drain piping can also need a permit. See whether you can do your own plumbing in Arizona.

HQ Plumbing & Air cuts out and replaces cracked cast iron drains, splices cast iron to ABS with shielded couplings, and repairs drains under slabs and in walls for homes and businesses across the Phoenix area. We're licensed and insured, with free estimates and upfront pricing. See our residential plumbing services.

Support it first, score it square, and join it with a shielded coupling. That's a clean cast iron cut.