Cast iron drain pipes: how long they last and signs they're failing

Cast iron was the standard drain pipe in American homes built through the 1960s and into the 1970s, so it’s common in Huntsville’s houses from that era. It can last a very long time, or it can fail well before you’d expect. The pipe’s age doesn’t tell you much on its own. What matters is what a camera sees inside it.

How long does cast iron last?

There’s no honest single number. Cast iron from the 1950s and 60s is still doing fine in plenty of houses. In others, the same age pipe is rusted down to a shell. It depends on the water that’s run through it, how it was installed, and plain luck. Think in terms of decades.

How cast iron drain pipe fails

Cast iron rusts from the inside out, and the rust doesn’t come off evenly. It builds up as scale that narrows the inside of the pipe, so even a pipe that isn’t leaking yet can be running at a fraction of its original capacity. On horizontal runs, the bottom of the pipe takes the worst of it, since that’s where water and waste sit the longest. Eventually the bottom rots through in a process plumbers call channeling, leaving a trough where waste seeps into the soil below. Cracks can also open up along the pipe, usually from ground settling or the iron getting brittle with age.

Signs your cast iron pipe is on its way out

• Slow drains all over the house, not just in one bathroom
• Backups that keep coming back after they’ve been cleared
• A sewer smell that comes and goes, especially near a floor drain or cleanout
• Rust colored stains or damp spots on the outside of a visible pipe, in a basement or crawlspace
• A musty smell or a wet patch of ground under the house where a line runs

Any one of these on its own could be something else. Together, or repeating, they’re worth a camera.

A house with PVC drains doesn’t have this problem, since plastic doesn’t rust or scale. Find out which material you’ve got under the house before you worry about the rest of this.

What the camera tells you that the age can’t

A camera run down the line shows the scale, the channeling, any cracks, and how much clear pipe is left to carry water. That’s the only way to know whether a specific pipe is failing, because two houses built the same year on the same street can have very different pipe under them. Cast iron can look ugly on the outside and be fine inside, and the reverse happens too.

Sewage backing up into a tub, shower, or floor drain means stop running water and call. A backup that keeps recurring usually means the pipe is close to a full blockage or a full failure.

Your options once cast iron is failing

• Spot repair. If the camera shows one bad section, that section can be cut out and replaced, usually with PVC, without touching the rest of the line.
• Full replacement. If the pipe is failing along its length, replacing the whole drain run is the more permanent fix, though it’s more work up front.
• Lining. A liner can sometimes go inside the old pipe without digging it up, but not every line is a good candidate. It depends on the pipe’s shape, its condition, and how many bends and connections stand in the way.

We replace cast iron when the camera shows it failing, and leave the rest alone. Plenty of it is still doing its job. If you’d like someone to run that camera and lay out the options, here’s how our sewer line repair work goes. And if your house also has original galvanized supply pipe, as a lot of them do, here’s what to watch for there too.