Cast-iron drain pipe is heavy, quiet and durable, and many homes from the 1960s and 70s still rely on it. In a slab-on-grade house, the drains from bathrooms, the kitchen and the laundry run through the soil beneath the concrete floor, then join the main drain that leaves the house.
Over time, the inside of cast iron corrodes. The bottom of the pipe, where water flows, can develop a rough, channeled surface, and scale builds up along the walls. That rougher, narrower pipe catches paper, hair and grease that would have washed through new pipe. In advanced cases the bottom of the pipe wears through, letting water into the soil under the slab.
Signs the cast iron itself may be the problem
Cleaning vs. repair
Both have a place. A camera inspection is usually what decides between them.
Cleaning (cabling or descaling)
- Restores flow in pipe that is rough but intact
- Some plumbers use descaling heads to smooth buildup
- Does not stop corrosion from continuing
- Can be a reasonable step while planning longer-term work
Lining or replacement
- Addresses corrosion, cracks and holes
- Lining can avoid breaking much of the slab where the pipe qualifies
- Replacement may mean cutting the slab or tunneling
- Larger projects that usually need a permit
What shapes the right choice
| Factor | Why it matters |
|---|---|
| How much of the pipe is affected | One bad section is a different job from a whole system |
| Whether the pipe still holds its shape | Lining needs pipe that can be cleaned and is not collapsed |
| Access | Cleanouts, wall access and where the pipe runs under the slab |
| Floor coverings and layout | Tile, hardwood and cabinetry affect how disruptive cutting the slab would be |
| Leaks into the soil | Active leaks under the slab change the urgency |
Questions to ask about cast-iron drains
- Can I see the camera footage of the sections you are concerned about?
- Is this corrosion throughout, or in specific sections?
- Is the pipe a candidate for lining, and if not, why?
- How would replacement be done in my home, and what would be disturbed?
- Does this work need a permit, and will you pull it?
Common questions
How long does cast-iron drain pipe last?
It varies with water chemistry, soil and use. Rather than relying on age alone, a camera inspection shows the actual condition.
Is jetting safe on old cast iron?
On sound cast iron it is commonly used. On pipe that is badly corroded or has holes, it can do damage, so a camera check comes first.
Do I have to replace all the drains at once?
Not always. Sometimes one section is far worse than the rest. Ask about options that address the worst areas first.
General information for Cypress, not a quote or professional advice. In an emergency, call 911.