How to Identify Cast Iron Pipes in Your Home: Visual Guide

Quick Identification Test

Here's the fastest way to tell if you have cast iron pipes:

Find an exposed drain pipe (check under sinks, in garage, or crawlspace)
Look at the color - Cast iron is dark gray to black
Knock on it - Cast iron makes a dull "thud," PVC makes a hollow "ping"
Check the weight - Cast iron is extremely heavy; plastic is light

If you passed all four tests, you likely have cast iron drain pipes.

Visual Identification Guide

Cast Iron Pipes

Characteristic	Description
Color	Dark gray, black, or rusty brown
Texture	Rough, often with bumps or rust spots
Sound when tapped	Dull thud
Weight	Very heavy (a 4" section weighs ~12 lbs/ft)
Joints	Hub joints with lead/oakum, or rubber couplings
Age	Typically in homes built before 1980

Where to look: Under kitchen sink, bathroom sink, in garage, basement, or crawlspace

PVC Pipes (Modern Replacement)

Characteristic	Description
Color	White or light gray
Texture	Smooth, shiny surface
Sound when tapped	Hollow ping
Weight	Light (a 4" section weighs ~1.5 lbs/ft)
Joints	Glued with purple primer visible
Age	Common after 1980

ABS Pipes

Characteristic	Description
Color	Black (can be confused with cast iron)
Texture	Smooth plastic surface
Sound when tapped	Hollow ring
Weight	Light (similar to PVC)
Joints	Glued with cement
Age	Used from 1960s onward

Pro tip: ABS is black like cast iron, but it's smooth and light. Cast iron is rough and extremely heavy.

Where to Check

Easy Access Points

1. Under the Kitchen Sink
Open cabinet doors and look at the drain pipe going into the wall. This is often the easiest spot to check.

2. Bathroom Vanity
Same idea—look under the sink at the drain connection.

3. Garage (if exposed)
Many Texas homes have exposed drain lines running through the garage ceiling or along walls.

4. Cleanout Access
Look for a cleanout cap (usually on an exterior wall or in the garage). The cap itself and surrounding pipe reveal the material.

Harder to Access

5. Crawlspace
If you have pier and beam foundation, you can see all drain lines underneath.

6. Attic
Vent stacks sometimes visible, though usually not the main drains.

7. Slab Foundation
Pipes are buried under concrete—you'll need a camera inspection to see these.

The Magnet Test

If you're still unsure, try this:

Get a refrigerator magnet
Touch it to the pipe
Cast iron: Magnet sticks strongly
Plastic (PVC/ABS): Magnet doesn't stick
Copper: Magnet doesn't stick (but copper is shiny reddish)

This works because cast iron contains iron, which is magnetic.

What About Mixed Systems?

Many homes have a combination of materials:

Common Scenario 1: Partial Replacement

Main sewer line: Cast iron (original)
Branch lines: PVC (replaced later)
Under sink: PVC (updated fixtures)

Common Scenario 2: Addition

Original house: Cast iron everywhere
Addition: PVC for new section

Common Scenario 3: Spot Repairs

Most pipes: Cast iron
Repaired sections: PVC patches with rubber couplings

Having mixed materials isn't necessarily a problem, but it tells you the system has been worked on.

If You Can't Find Exposed Pipes

Some homes have no easily visible drain pipes. Your options:

Option 1: Check Building Records

County appraisal district often has build date
Original building permits may list materials
Previous inspection reports (if available)

Option 2: Age-Based Assumption

Build Year	Likely Drain Pipe Material
Before 1960	Cast iron (almost certainly)
1960-1975	Cast iron (very likely)
1975-1985	Cast iron or early PVC
After 1985	PVC or ABS (likely)

Option 3: Camera Inspection

For $150-$350, a plumber will run a camera through your drains and tell you:

What material you have
Current pipe condition
Any problems developing

This is the only way to know for sure what's happening inside your slab.

What to Do If You Have Cast Iron

Having cast iron doesn't mean immediate emergency. Here's a decision framework:

Pipe Age	Condition	Recommended Action
Under 40 years	No symptoms	Monitor annually
40-50 years	No symptoms	Get camera inspection
40-50 years	Minor symptoms	Schedule assessment
50+ years	No symptoms	Proactive inspection recommended
50+ years	Any symptoms	Evaluate for replacement

Next: 7 Warning Signs Your Pipes Need Replacement →