Cast iron drain pipe, also called soil pipe, is grey iron cast in spinning moulds for drain, waste and vent lines. Older systems join lengths with hubs packed with oakum and poured lead; newer ones use rubber gaskets or no-hub couplings with stainless steel bands. It is magnetic, not galvanized, sized by nominal inside diameter, and cut with a snap cutter or abrasive blade once supported.
- Cast iron soil pipe is grey iron, cast in a spinning mould; in Canada it is made to CSA B70.
- Old hub joints were sealed with oakum and molten lead, so the pipe is iron but many joints contain lead.
- Nominal size roughly matches the inside diameter; the outside diameter differs from plastic of the same size, which is why transition couplings are specific.
- Soil pipe is not threaded and is not welded in drainage work; joints are mechanical.
- Before any cut in a stack, the pipe above and below must be supported so nothing drops.
01 /What is cast iron pipe, and what is it made of?
Cast iron drain pipe is made from grey cast iron, an iron alloy carrying a few percent carbon, much of it as flakes of graphite. Pipe lengths are centrifugally cast: molten iron is poured into a spinning mould, which throws it against the mould wall to form a dense pipe of even thickness. Fittings such as wyes, bends and cleanout tees are cast in sand moulds. In Canada, cast iron soil pipe, fittings and couplings are made to the CSA B70 standard.
It is called soil pipe because it carries soil (toilet) waste as well as greywater. Older pipe was dipped in a black bituminous, tar-like coating, which is why old basement pipe is often black under the dust; newer pipe carries a factory-applied protective coating. Cast iron soil pipe is not galvanized. Galvanizing is a zinc coating applied to steel pipe, a different and usually smaller pipe with threaded joints.
| Question | Answer |
|---|---|
| Is it magnetic? | Yes; a magnet sticks firmly |
| Is it galvanized? | No; galvanized steel is a different pipe |
| What is it coated with? | Older pipe: a black bituminous coating; newer pipe: a factory coating |
| Is it still used? | Yes, especially in multi-storey and noncombustible buildings |
| Is it heavy? | Yes; several times heavier than plastic pipe of the same size |
| Is it recyclable? | Yes, as ferrous scrap metal |
02 /Why was cast iron used, and when did houses stop using it?
Cast iron was the default drain material for most of the 20th century because it was strong, long-lived, noncombustible and quiet, and because the alternatives each did only part of the job: vitrified clay suited buried sewers, and galvanized steel suited small branches. Canadian residential construction moved to ABS and PVC through the 1960s and 1970s, because plastic was lighter, cheaper and faster to install, and by the late 1970s most new houses were plumbed in plastic.
Cast iron never disappeared. It remains common in apartment and condo towers, hospitals and other buildings where fire rules restrict combustible pipe, and in walls beside bedrooms where drain noise matters. So the answer to 'is cast iron pipe still used' is yes, just rarely in new single-family houses.
Older houses, such as those in Calgary's inner-city and postwar communities, often keep original cast iron under the basement slab even after upper floors were replumbed in plastic; see pipe cleaning in Calgary. If you are not sure what you have, What Pipe Do I Have? walks through the clues.
03 /How are cast iron pipes joined?
Cast iron pipes are joined mechanically, not glued or welded. Three joint systems cover almost everything in Canadian houses, plus a threaded system found in some older buildings.
| Joint | How it is made | Where you find it | How to recognize it |
|---|---|---|---|
| Hub and spigot, lead and oakum | The plain spigot end sits in the bell (hub) of the next length; oakum, a tarred hemp or jute fibre, is packed in, then molten lead is poured and caulked tight | Older houses | A wide bell with a dull grey metal ring at its mouth |
| Hub and spigot, compression gasket | A rubber gasket sits in the hub and the spigot is pushed through it | Later installations | A wide bell with a rubber lip showing |
| No-hub (mechanical joint) | Plain pipe ends butt together inside a neoprene sleeve held by a stainless steel band with clamps | Most newer cast iron | A shiny corrugated steel band with screw clamps |
| Threaded drainage fittings | Threaded cast iron fittings on galvanized steel pipe | Some older buildings | Threads at every fitting; smaller pipe |
Can cast iron pipe be threaded? Cast iron soil pipe itself is not threaded. When you see threads on an old drain, they are almost always on galvanized steel pipe screwed into a threaded cast iron fitting.
Can cast iron pipe be welded? Grey cast iron is not welded in drainage work. It is brittle and prone to cracking when heated unevenly, so every joint and repair is mechanical. Ductile iron, used for water mains, behaves differently; see ductile iron pipe and pipeline cleaning.
04 /Do cast iron pipes have lead?
The pipe is iron, but older hub joints contain lead, poured as a molten ring over the oakum and then caulked tight. In a drain system that lead is not in contact with your drinking water, so it is not a drinking water concern in the way a lead water service line is. It matters when the joints are disturbed.
- Cutting or grinding through a lead joint throws lead dust.
- Heating or melting a joint gives off lead fume.
- Knocking out an old joint scatters lead fragments.
- Sanding or scraping painted pipe can add lead paint dust in older homes.
05 /How is cast iron pipe measured, and what sizes are common?
Cast iron is sold by nominal size, which roughly matches the inside diameter. The outside diameter is larger and does not match ABS or PVC of the same nominal size, which is why a coupling joining cast iron to plastic is made for that specific pair.
| Nominal size | Approximate outside diameter | Typical use in a house |
|---|---|---|
| 1-1/2 in | About 48 mm (1.9 in) | Some older branch drains |
| 2 in | About 60 mm (2.35 in) | Branch drains and vents |
| 3 in | About 84 mm (3.3 in) | Stacks and toilet branches in some houses |
| 4 in | About 110 mm (4.3 to 4.4 in) | Main stacks and building drains |
| 6 in | About 160 mm (6.3 in) | Larger buildings and some laterals |
To measure, wrap a string or flexible tape around the pipe, measure the circumference, and divide by 3.14 to get the outside diameter. Match it to the nearest line in the table. For comparison, 4-inch ABS or PVC drain pipe is about 114 mm (4.5 in) outside.
Cast iron is heavy: a 3 m length of 4-inch soil pipe typically weighs more than 30 kg. That weight is why stacks are held by riser clamps at floors and by hangers along horizontal runs, and why cutting one is a two-person job.
06 /How do you cut cast iron pipe safely?
Cast iron is cut with a soil pipe snap cutter, a reciprocating saw with a carbide-grit or diamond blade, or an angle grinder with a metal-cutting or diamond wheel, and only after the pipe on both sides of the cut is supported.
| Tool | How it works | Strengths | Drawbacks |
|---|---|---|---|
| Snap cutter (chain cutter) | A chain of cutting wheels wraps the pipe and is tightened until the pipe snaps | Fast, clean, little dust; ratcheting models work in tight spaces; commonly available from tool rental shops | Can crush thin or corroded pipe instead of snapping it cleanly |
| Reciprocating saw | A carbide-grit or diamond blade abrades through the wall | Works almost anywhere | Slow; wears blades; vibration and noise |
| Angle grinder | An abrasive or diamond wheel grinds through | Quick on exposed pipe | Sparks, dust and kickback; needs room to work |
Can you cut cast iron pipe with a Sawzall-type reciprocating saw? Yes, with a blade made for cast iron. Ordinary bimetal blades dull quickly. Run the saw at moderate speed, keep the pipe supported so it cannot pinch the blade, and expect it to take several minutes on a 4-inch pipe.
Cutting in a tight space: a ratcheting snap cutter needs only a short handle swing, and a reciprocating saw with a short blade fits where a grinder will not. Sometimes the practical answer is to cut a little above or below the ideal spot, where there is room.
- Stop all water use
Tell everyone in the house, and plug or drain the section so nothing flows while it is open.
- Support the stack
Install riser clamps or strong strapping above and below the cut so the upper section cannot drop and the lower hub cannot shift.
- Mark and cut square
A square cut seals properly in a coupling. Keep lead joints out of the cut line where possible.
- Look inside
The cut end shows the true wall thickness and the state of the invert, which is useful evidence.
- Join with approved couplings
Cast iron to cast iron uses a no-hub coupling; cast iron to ABS or PVC uses a transition coupling rated for both outside diameters, often a shielded type where the code calls for it.
- Test before closing up
Run water through every connected fixture and check the joints.
07 /Is old cast iron pipe worth anything?
Old cast iron is recyclable as ferrous scrap. Its value per kilogram is low compared with copper or brass and moves with metal markets, so removed pipe usually matters more for disposal than income. Scrap dealers may ask for lead from old joints to be separated. For what to do with pipe that is still in the house, and how to tell whether it has years left, see how long cast iron drain pipes last, and for cleaning it, cast iron drain pipe cleaning.
FAQQuestions people ask
Is cast iron pipe magnetic?
Yes. A magnet sticks firmly to cast iron, and to galvanized steel. It separates iron and steel from plastic, clay, copper and brass, but not cast iron from galvanized.
Is cast iron pipe galvanized?
No. Galvanizing is a zinc coating on steel pipe. Cast iron soil pipe is bare or coated with a black bituminous or factory coating, is usually larger, and uses hubs or banded couplings rather than threads.
Can cast iron pipe be threaded?
Cast iron soil pipe is not threaded. Threads on an old drain are on galvanized steel pipe screwed into threaded cast iron fittings.
How is cast iron pipe connected to PVC or ABS?
With a transition coupling sized for the cast iron outside diameter on one side and the plastic on the other, usually a rubber sleeve with stainless steel clamps and often a stainless shield. The coupling type allowed depends on the code and location.
Can you cut cast iron pipe with a Sawzall?
Yes, with a carbide-grit or diamond blade made for cast iron. Support the pipe on both sides first, expect a slow cut, and avoid cutting through old lead joints.
Why is cast iron still used in apartment buildings?
Because it is noncombustible, which suits buildings where fire rules restrict plastic pipe, and because its weight makes drains much quieter in shared walls.
Do cast iron pipes have lead?
The pipe is iron, but older hub joints were sealed with poured lead over oakum. That lead matters when joints are cut, heated or knocked out, not during normal drain use.
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