Cast Iron Pipe vs. PVC Pipe

 by Tim Carter

Founder of the

If you've not seen the guts of an old home, I'm talking about one built before 1920, you might not have ever seen cast iron drain pipes. It was the gold standard piping material used by plumbers for larger drain and vent lines for decades.
But the chemical industry explosion that happened in the 1960's changed the course of plumbing. Some may argue not for the better.

Don't Believe All You Hear
Cast iron piping has not given up the ghost. Many homeowners associate cast iron piping with antiquated plumbing that's prone to developing leaks. Often people think that it clogs quite easily.
Conversely, many people think that modern plastic PVC plumbing piping is the miracle material. Well, both materials have advantages and disadvantages. Let's talk about both types of pipe and see what you think.

That Old Black Metal

Cast iron piping has been used successfully in plumbing systems for hundreds of years. In fact, in the year 1623 cast iron pipe was installed in the Fountains of Versailles in France.
That same piping is still functioning today. Thousands of miles of municipal water and sewer systems use cast iron pipe. The reason is long-term durability. Cast iron simply lasts.


Virtually every residential home built prior to 1960 had some form of cast iron piping in its drainage system. The primary drainage stacks or pipes within the walls were constructed of cast iron.
The branches off of these stacks which connected to sinks, toilets, and tubs often used lead piping or galvanized-iron pipes.

Galvanized Branch Arms
Galvanized iron piping is especially prone to clogging. Within a decade or two of installation, the galvanized coating on the inside of the pipe wears always or corrodes.
When this happens, the iron starts to rust and deposits start to form on the inside of the pipe causing the inner diameter of the pipe to constrict and get smaller and smaller.
I've personally removed hundreds of these pipes which connected to kitchen or bathroom sinks. In virtually every instance, these pipes were clogged solid.

Cast Iron Stacks Wide Open
However, the cast iron vertical drain stacks only two to three feet away from the sinks were completely free of obstructions. Unfortunately, many homeowners and young plumbers don't realize these phenomena and falsely accuse the cast iron as a poorly performing product.

Cheap Labor & Cast Iron
Years ago, residential construction labor costs were insignificant. Time was not always an issue with respect to how long a particular task took to complete.
For example, imagine how long it took to nail on those thin lath boards which allowed the plaster to be applied to the walls and ceilings of houses.
Think of the amount of time it took carpenters, using hand tools, to mortise hinges and locks into doors. The same is true for old style cast iron piping.

Lead & Oakum
Old style cast iron piping was a chore to install. The plumbers had to pack oakum into each joint. Oakum was simply an oil-soaked rope that filled the 3/8-inch-wide gap where the male end of one cast-iron pipe mated up with the female hub of another piece of cast iron.
Once the oakum was taped tight into the joint and within a half-inch of the top of the hub, the plumbers would melt lead ingots and then pour this molten lead into the hub.
The lead solidified rapidly and the plumbers would use a flat tool to tamp and pack the lead in the hub so the joint became leak-free.
The job of installing cast iron was tough, time-consuming and dangerous.

Modern Cast Iron Pipe
The cast iron pipe available today looks somewhat similar to old cast iron. Old cast iron was indeed cast in molds. Modern cast iron is spun cast so the pipe wall thickness is much more consistent.
The methods of installing the material have changed drastically. Gone are the oakum and molten lead. In their place, you now find vulcanized rubber seals and stainless steel band clamps.
Cast iron piping systems can now be installed in a fraction of the time it took to install them fifty years ago. In fact, modern cast iron piping can be installed just as quickly as plastic PVC piping.

Adjustable Fittings
One of the amazing aspects of the modern cast-iron pipe is the fact you can easily adjust the orientation of the fittings AFTER you install them. You can do this by just loosening the screws on the band clamps and then twisting the fitting.
It's IMPOSSIBLE to do this with PVC or old cast iron. Once you glue PVC together you have between five and two seconds, depending on the diameter of the pipe, to make any adjustments.
With old cast iron, once you poured in the molten lead, you're toast. You can't make any adjustments.

Super Quiet
Because cast iron is dense, it takes a lot to get it to vibrate. When water flows down a cast iron stack, you can only hear it if you put your ear up to it.
If you need to have a quiet home and don't want to hear a waterfall in your walls each time someone showers or flushes a toilet, then you want cast iron drain pipes.

PVC Pipes
I've been a master plumber since before I was thirty years old. I had the good fortune to work with both cast iron and modern PVC.
PVC pipe is lighter weight than cast iron. It cuts faster with a regular saw you'd use to cut lumber. To cut cast iron, you need a cut-off saw with an abrasive blade that creates a shower of sparks.
To cut a 3-inch piece of PVC pipe, you might take three or four seconds. To make the same cut on cast iron with a cut-off saw, you'll spend at least 15 or 20 seconds.

PVC Is Noisy

PVC is not dense and water cascading down a vertical stack causes it to vibrate. This vibration creates lots of noise.
People who are not familiar with PVC pipe often think there's a leak inside a wall when they hear a toilet flushed for the first time. It's annoying in my opinion.


© 2017 by HENGTONG PIPE AUSTRALIA Pty. Ltd. Proudly created with Owen Zhao

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