The toilet in a house built before 1970 sits on a cast iron flange connected to a cast iron drain pipe that runs through the floor and into the main waste stack. The flange has been there for fifty or sixty years. The closet bolts that hold the toilet down have rusted to the point where a wrench rounds off the nut. One of the ears that holds the bolt has snapped off. The flange itself is pitted and flaking, and when you scrape off the old wax ring, pieces of the flange come with it. Cast iron is unforgiving to work with. It is heavy, brittle, and connected to the drain pipe in a way that makes removal difficult and replacement a choice between specialized tools and creative workarounds.
Replacing a cast iron toilet flange is a different job from replacing a PVC flange. PVC is cut with a saw. Cast iron is cut with a grinder or a snap cutter, or it is separated at a leaded joint that has not been disturbed in half a century. The difficulty of the job depends on how the existing flange is connected to the pipe, whether the flange is broken or merely rusted, and whether the cast iron pipe below it is in good enough condition to accept a new connection. A cast iron flange that is rusted but structurally intact may need only a repair ring. A flange that is broken at the pipe connection must be cut out or unsealed, and that is where the job becomes substantially more difficult.
Assess the Flange Before You Touch It
Remove the toilet as described in any standard toilet removal procedure. Scrape off the wax ring and clean the flange surface with a rag. Do not use water. You are trying to keep debris out of the drain, not wash it down. Stuff a rag into the drain opening.
Determine how the flange is connected to the pipe. A cast iron flange in a house built before about 1960 is probably leaded into a cast iron pipe. The joint between the flange and the pipe is filled with molten lead that was poured into the joint and packed with oakum, a hemp fiber that swells when wet and forms the initial seal. The lead is visible as a silver-gray ring around the base of the flange where it meets the pipe. A leaded joint is watertight for decades, but the lead can be drilled out and the flange can be pried free. A cast iron flange in a house built between about 1960 and 1970 may be connected with a compression gasket, a rubber seal that is compressed between the flange and the pipe when the flange is tightened down. A compression gasket flange can be unbolted and lifted off. A cast iron flange that is part of the pipe itself, cast as one piece with the pipe hub, cannot be removed without cutting the pipe.
If the flange is rusted through in multiple places, or if the pipe itself is rusted and pitted, replacing the flange may require replacing a section of the pipe. Cast iron drain pipe rusts from the inside out. The exterior may look solid while the interior has rusted to half its original thickness. Tap the pipe gently with a hammer. A solid pipe rings. A rusted pipe thuds. If the pipe sounds dead, it may need to be replaced, and replacing cast iron drain pipe inside a finished floor requires opening the ceiling below or the floor above. That is a plumber’s job.
The Repair Ring — Fix the Flange Without Removing It
If the cast iron flange is solid except for a broken closet bolt ear or a surface that is too pitted to seal a wax ring, a repair ring solves the problem without removing the existing flange. A repair ring is a stainless steel or galvanized steel ring that sits on top of the existing flange and provides new closet bolt slots and a smooth sealing surface. It is screwed into the floor through the existing flange mounting holes. The repair ring does not touch the pipe. It covers the old flange like a reinforcement plate.
Choose a repair ring that is the same diameter as the existing flange. Position it so the closet bolt slots are perpendicular to the back wall. Mark the screw holes through the repair ring onto the floor. If the floor is concrete, drill pilot holes with a hammer drill and a masonry bit and secure the ring with Tapcon screws. If the floor is wood, use stainless steel screws. Tighten the screws until the ring is flush and immobile. Install a new wax ring on the toilet, set the toilet on the repair ring, and bolt it down. A repair ring costs fifteen to twenty dollars and takes twenty minutes to install. It is the correct solution for the majority of cast iron flanges that are rusted but not broken.
Removing a Leaded-In Cast Iron Flange
If the flange is broken at the pipe connection, or if the lead joint is leaking, the flange must be removed. A leaded-in flange is removed by drilling out the lead. The lead is soft. A quarter-inch drill bit goes through it like it goes through wood. Drill a series of holes around the circumference of the flange where it meets the pipe, drilling into the lead joint between the flange hub and the pipe. Space the holes about half an inch apart. Do not drill into the cast iron pipe. The drill bit will tell you when it hits iron. The sound changes, the resistance increases, and the bit stops cutting.
Once you have drilled a ring of holes around the joint, insert a flathead screwdriver into one of the holes and pry. The lead between the drilled holes will break, and the flange will begin to loosen. Work around the circumference, prying gently. Cast iron is brittle. Prying too hard will crack the pipe, and a cracked cast iron pipe inside the floor is a problem that requires opening walls or ceilings to replace. Once the lead is broken free, lift the flange off the pipe. The oakum packing will be visible in the gap between the pipe and the flange hub. Remove as much of it as you can with a screwdriver or a pick.
Clean the inside of the pipe hub with a wire brush. The surface must be clean and free of old oakum and lead residue for the new flange to seal. If you are installing a new cast iron flange, you will need to pour a new lead joint, which requires a lead pot, a ladle, oakum, and a pouring rope, and is a skill that takes practice. The alternative for a homeowner is a compression flange or a push-in flange that seals with a rubber gasket and does not require lead.
Installing a New Flange on a Cast Iron Pipe
A push-in replacement flange, also called a compression flange or a twist-and-set flange, is the simplest option for a cast iron pipe. The flange has a rubber gasket on the bottom that fits inside the pipe. You push the flange into the pipe, and as you tighten the adjustment screws or twist the locking ring, the gasket expands and seals against the inside of the pipe. No lead. No glue. No special tools. A push-in flange costs about twenty to thirty dollars and works on cast iron, PVC, and ABS pipes.
Insert the flange into the pipe until it sits flush on the floor. If the flange sits above the floor because the rubber gasket bottoms out on a ledge inside the pipe, trim the gasket with a utility knife until the flange sits flush. Tighten the adjustment screws evenly, alternating between them so the gasket expands uniformly. A gasket that is tightened more on one side than the other will leak. Once the flange is secure, drill pilot holes through the mounting holes into the floor and secure the flange with concrete anchors or wood screws. The push-in gasket holds the flange to the pipe. The screws hold the flange to the floor. Both connections are necessary.
Set the toilet on the new wax ring, bolt it down, and reconnect the water. Flush several times and check for leaks at the base of the toilet and at the flange connection. A properly installed push-in flange on a clean cast iron pipe will seal for the life of the toilet.
FAQ — Cast Iron Toilet Flange Replacement
Can I connect a PVC flange to a cast iron pipe instead of using a cast iron or push-in flange?
Yes, using a rubber coupling called a Fernco or a Mission coupling. The coupling is a thick rubber sleeve with stainless steel band clamps that connects cast iron to PVC. Cut the cast iron pipe below the flange with a reciprocating saw and a diamond blade, or with a snap cutter rented from a tool rental company. Slide the rubber coupling over the cast iron pipe, insert a short section of PVC pipe into the other side of the coupling, and glue a PVC flange onto the PVC pipe. Tighten the band clamps to the manufacturer’s torque specification. A Fernco coupling is code-approved for above-ground connections in most jurisdictions and is the standard method for transitioning from cast iron to PVC.
The new flange sits a quarter inch above the finished floor. Is that a problem?
A quarter inch above the floor is within tolerance. The wax ring will compress to fill the gap, and the toilet will sit flush. If the flange sits more than a quarter inch above the floor, the toilet will rock, and rocking will crack the wax seal and eventually crack the toilet base. If the flange is too high because the pipe extends above the floor, cut the pipe down. If the flange is too high because the push-in gasket will not seat deeper, a different flange model with a shorter gasket or a flange that glues inside the pipe may be required. Do not shim the toilet to accommodate a high flange. Shimmed toilets rock.
Is drilling out a lead joint dangerous?
Lead is toxic. The drilling produces lead chips and lead dust. Wear a respirator with a P100 filter, not a dust mask. Wear gloves. Cover the area with plastic sheeting taped to the floor. Vacuum the lead chips with a HEPA vacuum, not a standard shop vacuum. Wash your hands and arms thoroughly when the job is done, and wash your work clothes separately from other laundry. A single lead joint removal produces a small amount of lead waste, but lead accumulates in the body over a lifetime. Treat every exposure seriously. If you are uncomfortable working with lead, hire a plumber. The cost of professional removal is less than the long-term health cost of repeated lead exposure.
Last modified: June 13, 2026
