The short answer
Cast iron was the standard drain pipe in Northern Virginia houses until plastic pipe took over around the 1970s, and a lot of it is still working. It’s often said to last 50 to 100 years, but it rots from the inside, along the bottom where the water runs, so you can’t judge it by how it looks from outside. Rust stains, drains that keep slowing down and a sewer smell are the signs. A camera tells you whether it needs a cleaning, a patch or replacing.
How to tell if you have it
- It’s dark gray or black, often with rust showing, and much thicker and heavier looking than plastic.
- Tap it with a screwdriver handle. Cast iron rings like metal. Plastic sounds dull and hollow.
- A magnet sticks to it.
- Older runs have bell joints, a wider collar every few feet where one length fits into the next. Newer cast iron uses rubber couplings with steel bands.
- The main stack, the big vertical pipe in the basement, is the easiest place to look.
A lot of houses here built from the 1950s into the 1970s have cast iron inside and something else from the foundation out to the street, often clay or Orangeburg. What pipes does my house have? covers every kind, and Orangeburg pipe covers the tar paper one.
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How cast iron fails
Water and waste run along the bottom of a horizontal pipe. Over decades that bottom strip corrodes and wears thin, a crack opens along the length, and eventually the bottom of the pipe is mostly gone. Plumbers call it channel rot. It’s worst in long horizontal runs, especially under a basement slab, where nobody sees it until the floor or the soil under it is wet.
Inside, rust and scale build up in lumps along the wall. Paper and grease catch on the lumps, so the pipe gets narrower and clogs more often, even when nothing unusual went down it.
Signs your cast iron is going
- Rust colored stains, flakes or a damp line on the outside of the pipe, often at a joint or along the bottom.
- A crack you can see running along the length.
- Drains that keep slowing down after they’ve been cleared, because the scale inside catches everything.
- A sewer smell in the basement with no clog. What a sewer smell means.
- Small flies hanging around a basement drain.
- Damp spots or new cracks in the basement floor along the drain line.
- A water stain on the ceiling under a bathroom.
Your options
Old cast iron isn’t automatically bad. A solid cast iron line is quieter than plastic, and if the camera shows round pipe with sound walls, there’s nothing to fix. When it isn’t solid, here’s what we do:
- Descale it. A drain machine with a chain head knocks the rust and scale off the inside wall, then hydro jetting washes it out. The pipe drains like it should again, and the camera afterward shows the real wall. Descaling a pipe with thin walls can open a hole, which is why we look first.
- Replace a section. A cracked or rotted piece gets cut out and replaced with PVC, joined to the good cast iron on each end with banded rubber couplings. This is the usual fix on a basement stack or an exposed run.
- Line it. Where the pipe is worn but still in one piece, a new pipe can be cured inside the old one without tearing out walls or the slab. Trenchless sewer repair covers how.
- Replace the run. When the bottom is gone, it’s a new PVC line, and under a slab that means cutting the floor. What a new sewer line costs has the prices with the monthly payments next to them.
Start with the camera
From outside, a cast iron pipe that’s fine and one that’s nearly through on the bottom look the same. A camera down the line, $89 added to a visit, shows the inside wall, the scale and any cracks, and you watch the footage with us. Clearing a slow fixture line runs $200 to $800, and the main line runs $550 to $1,650. Buying a house built before the 1980s? Put a camera down the drains before you close. When a sewer camera inspection is worth it.
Don’t wait for the leak
Cast iron gives you years of warning if you know what to look at. Rust on the stack, a drain that keeps slowing down and a smell you can’t place are the early signs, and they cost a lot less to deal with than a wet basement floor. Error codes and warning lights at home covers the other signs a house gives you before something breaks.
When you’d rather we do it
A sink clogged at the trap is $99 with our sink clearing offer, up to the P-trap. A toilet, tub, shower or any drain past the trap is drain cleaning, $200 to $800. The main line to the street runs $550 to $1,650, and when grease or roots keep coming back, hydro jetting clears the pipe wall. You get the price before we start. A plumbing diagnosis visit is $49, or $250 after hours.
Call (703) 997-9757, day or night, or see every current deal on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
How long does cast iron drain pipe last?
It’s often said to last 50 to 100 years. Where yours lands depends on the water, what’s gone down it and how it was installed, and a camera shows its real shape.
How do I know if my cast iron pipes are bad?
Rust stains or flakes on the outside, a crack along the length, drains that keep slowing down and a sewer smell are the common signs.
Should I replace cast iron with PVC?
Only the parts that are failing. Sound cast iron can stay, and it’s quieter than plastic. Cracked or rotted sections get replaced with PVC.
What is channel rot in cast iron pipe?
The bottom of a horizontal pipe corroding and wearing through from the inside, where the water runs. It’s worst under basement slabs.
Can cast iron pipe be descaled?
Yes. A drain machine with a chain head knocks the scale off the inside wall, and jetting washes it out. A camera first makes sure the walls are thick enough.
