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PVC Pipe vs. Cast Iron Pipe

PVC Pipe vs Cast Iron TIPS

The Old Gold Standard

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.

CLICK HERE to get FREE & FAST BIDS from local plumbers that can install PVC or cast-iron pipe in your home or business.

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.

Pre-Plastic

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 aways 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 this 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 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.

CLICK HERE to get FREE & FAST BIDS from local plumbers that can install PVC or cast-iron pipe in your home or business.

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 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 Pipe Videos

Watch this video to see how easy it is to glue PVC pipe together. Primer is mission critical!

Watch this video to see different PVC fittings you use with pipe.

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.

CLICK HERE to get FREE & FAST BIDS from local plumbers that can install PVC or cast-iron pipe in your home or business.

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12 Responses to PVC Pipe vs. Cast Iron Pipe

  1. I'm in the process of cutting out and replacing some rusty, leaky cast iron pipes that are clogged solid, so the assertion that they are somehow clog proof doesn't add up.

    • Well, perhaps they're full of grease or they were abused. The point I was trying to make is that cast iron has a rich history of not producing expanding scale on the inside of the pipe like galvanized iron.

  2. Thanks for the info, but I feel the article was lacking. We're in the process of deciding to spend thousands of dollars redoing some plumbing and the obvious choice is PVC. Plumbers are certainly pushing for that. They say cast iron will last 40 years whereas PVC will last a lifetime. I have my suspicions about that, and like you feel that cast iron must have some pros.

    A lot of times, I feel like a guy will try to sway you to go the route thats easiest for them to install (or do it how they always done it instead of trying a new way...which in this case would be old school), rather than doing it the way it will last the longest. Thats what we want to know about Tim. The details. Why does the title say Cast Iron vs. PVC and then contain zilch about PVC? Tell us about schedule 50 vs scheudle 80 PVC, and how 80 would stand the test of time? What are the negative aspects of PVC besides sound and no long term testing (hasnt been around as long as cast)? How do each resist tree root intrusion, and handle the cold elements in the midwest?

    I've always enjoyed your articles and videos. Would highly appreciate if you could do an update and provide us with some more details. Especially since most modern plumbers will be looking at us like we're crazy if we suggest Cast Iron! Thanks

    • There's no need for an update. Cast iron has stood the test of time for hundreds of years. For me it's a sound issue. PVC is just too noisy. Cast iron costs more no doubt, but just use it for the stacks if necessary to cut down on noise. PVC can be used for branch arms and all venting.

      • I am going to renovate my bathroom . In my basement I have the black cast iron pipe for the main drain going outside to pvc pipe that goes into the city sewer system. I was told that the black cast iron drain pipe which is a 3-4 inch pipe has to be replaced by pic pipe. The cast iron pipe is leaking at one joint. Does anyone know the code about using the existing cast iron main drain pipe or do I have to replace it with pic piping

      • Great. It is good to know the pros and cons of cast iron. It is definitely not all bad. But currently, insurance companies are mostly concerning other drain pipe than PVC.

  3. Cast Iron Pros: Tough, resistant to being cut or impacted (unless you notch it and hit with a hammer). Can be abused with a drain snake without scraping off the pipe wall. Long lasting unless you put a lot of chemicals down it or run concentrated stuff like urine from a flushless toilet. Then it will corrode quickly. Quiet

    PVC Pros: Low cost, light, fast and easy to install, smooth inside so it's not likely to get plugged up. Totally corrosion resistant unless you dump something like straight painters solvent down it. It's been around for sixty years and should give you a minimum of 50 years service.

  4. Thanks for the article. We are redoing a house built in 1916. The cast iron was in perfect shape! We are only removing it because we felt it could be prone to cracking during the demolition process. However, I am concerned about the use of rubber gaskets vs the old lead. I can't image the rubber will last 100 years just as the current pipes did.

  5. I have to decide between PVC and metal by next week, the cast iron pipe in my house is last probaly 100 years, the plumbing keep telling me no one using cast iron anymore, I dont know the plastic pipe will hold till 100 years the cost is just about $1000 higher, I think I'll go with metal , it's for the sewer main pipe.

  6. I have a pin hole leak in the iron pipe. A plumber friend of mine told me to wrap it with rubberized electrical tape and it should rust back into the pipe. Will give it a try .

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