Cast Iron Stack Crack--Why?

11 years ago

Hello,

I wasn't sure whether to post here or in Plumbing.

We just discovered a significant leak in the main cast iron stack of our 3-story + basement 100 year old home. We found the crack behind the second floor toilet after removing a bit of drywall.

The current plan is to professionally cut out that section and replace accordingly. I am in a conundrum though as to whether some preventative replacement would be worthwhile.

We are currently in the midst of a first floor kitchen renovation and the entire stack is currently exposed down through the basement. The top (third floor) is still behind the wall and presumably damage-free.

I understand that cast iron is a great insulating product and should last for a LONG time. I am inclined to keep the cast iron in-tact but if this is a sign of things to come, I suppose I should replace more.

Does anyone know the reason for a crack in the cast iron? Is one crack symptomatic of future cracks?

Thanks.

Featured Answer

rwiegand

11 years ago

last modified: 9 years ago

hollysprings-- Having replaced several cracked PVC pipes and fittings over the last decade I think you are overly optimistic. I'd bet on ancient cast iron outlasting new plastic any day. Not to mention that listening to the whoosh of water in the PVC pipe across the living room ceiling and down the wall after each flush upstairs became a family joke.

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Comments (8)

User
11 years ago
last modified: 9 years ago
It's old and brittle. What other reason do you need? I'd personally replace it with PVC and additional sound insulation and never have to ever worry about it again.
worthy
11 years ago
last modified: 9 years ago
I'd replace the damaged section and wait and see. Cast iron soil pipes are commonly said to have a 100+ year lifespan but that's a minimum and many are functioning well beyond that time period. If it cracks again, it'll be time eonough to change out the whole stack.
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Re: "You don't want anything not made in the USA. It might contain lead." Baldersash. Unlike things made a ceramic coating, which might well contain lead, it would be almost impossible for cast iron to contain lead. Why? Lead melts at 327 C, whereas iron doesn't melt until 1535 C. In fact, lead would be boiling (1748 C) at the temperatures that cast iron is worked (roughly 2000 C)! This means it would be leaving the molten iron via the air, so it cannot be in cast iron. Besides which, lead is more expensive that iron, and less plentiful, so there is every incentive to remove it and sell it! Now, as to buying Chinese made articles for political or ethicial reaons, I cannot comment.
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Find am experienced plumber. A new piece of no hub cast iron may be the most cost effective fix. While there are now requirements for intermediate supports for cast iron stacks, they did not always exist. I have seen 4 story stacks holding their own weight up with no other supports. It becomes a real chore to even attempt to make repairs on them.
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The threads are most likely directly into the cast iron. When you break a pipe off it usually leaves a ring of the broken pipe inside the female fitting that needs to be removed. This rung can be cut with a fine tooth hacksaw (32 TPI) and then removed. A real plumbing supply house will have powdered sealers that mix with water. They are a very fine grain version of cement. This is applied to the remaining threads in the cast iron and a new nipple screwed into place (or even a NPT to slip PVC fitting). The sealer will conform to the outside of the new threads and form a complete seal. You could even unscrew the fitting and examine the 'molded in place' threads if you wanted (pipe dope will then be needed when you put it back together). I do this type of stuff enough to own the IPT taps needed to actually chase the threads, but even that sometimes fails to make a joint that will come up tight. The 1.5 IPT tap runs about $80
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The fact that the stack is 50 years old is not a cause for concern, I have worked on stacks that are over 100 years old and still in excellent shape. NO doubt the cleanout caps are stuck in place, but they can usually be removed with a 6ft pipe wrench. If not, we simply break the cap out, clean the line and install a new cap, not a big deal. Tying into the drain below the basement floor should not pose any problems with the stack if done correctly. The real reason you want to change the stack is because you perceive that the branch lines will interfere with where you want to build walls. The problem with that idea is that the placement of those branch connections are finitely regulated by numerous code requirements and in all probability cannot be moved to a place more to your liking with a major revision of your entire DWV system. Now in regards to attaching another vent to that stack. You may not attach an auxiliary vent to that stack until the auxiliary vent reaches an elevation at least 6" higher than the flood level rim of the highest fixture served by that stack, which is no doubt on the top floor of your structure. Even aside from all of those problems, removing a cast iron stack is dangerous enough when done by trained professionals. It is not an undertaking that should ever be attempted by amateurs.
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columbusguy1
11 years ago
last modified: 9 years ago
Depending on the size of the crack, I have seen rubber gaskets put on with clamps at top and bottom. Since the pipe only holds water for a brief time, you should have no problems after that. You might also try some epoxy filler--it worked nicely on a cracked copper water pipe for me.
lazypup
11 years ago
last modified: 9 years ago
In regards to the service life of Cast iron, there are some cast iron soil pipes in Europe that were installed by the Romans in the 3rd or 4th century and they are still working fine.

Before we begin the discussion of the why & how of your problem I want to caution you very carefully that repairing a cast iron vertical stack is not by any means a DIY project.

You stack is made with cast iron "hub & spigot" pipe, which means the pipe is simply cut off straigth across the pipe on the discharge end, leaving was is known in the plumbing trade as a "Spigot" end. On the upstream or input end it has a broadened cup shape,called a "Hub", that a spigot end is set into then the hub is packed with oakum, which appears like frayed hemp rope that is impregnated with an oil material. After the oakum is packed in they poured about a 1/2" to 3/4" thick layer of molten lead in the hub to complete the seal.

Hub & spigot CI pipe is extremely strong and generally it is capable of being self supporting when installed in a vertical stack however the codes do require additional supports at specified intervals as the stack rises. Generally as they attached horizontal branch lines to the stack they placed wooden blocking under the branch line close to the stack to provide the required support and in some cases they installed additional steel perf tape hangers. The problem here is that very often the steel perf tapes have long since rusted away and the stack is left supporting itself.

The next problem is that as the structure settles over the years it the wooden bracing often looses contact with the pipe, which again leaves the stack self supporting and often as the house settles a long branch line settles until it is actually causing a leverage force against the stack.

While CI is very strong it is also a brittle metal so as the forces of self supporting the weight plus any leverage forces are applied to the stack, the stack is rigid and in time the force on the vertical stack causes a section to crack vertically.

The proper course of action is to cut out the damaged section and replace it. The section can be replaced with no-hub cI or PVC but you must be aware that when you cut the pipe in all likelihood there is no support on that pipe above the cut and you run an extremely high risk of the entire remainder of the stack to come crashing down on you. Do not take this lightly as CI pipe weighs approximately 10 pounds per linear foot and a stack from the basement to the roof in a two story house can easily weigh in at 400 to 500lbs. Just imagine an V-8 engine block poised and ready to fall when you cut the pipe.

It really takes some serious measures to provide support to the stack before making the cut.

I once saw a guy cutting a short section out in a basement and the moment he completed the cut, the entire stack fell straight down in a heartbeat. Fast enough that it hit his foot before he had a chance to move and he had 4 toes instantly cut off, not to mention that it also ripped horizontal branch lines all the way up the stack so they had to open all the walls and replace the line all the way up to the roof...

This is one job that is best left to the pro's who have both the experience and the necessary equipment to support the stack while repairing it.
User
11 years ago
last modified: 9 years ago
Modern cast iron waste pipes use the rubber gaskets you mentioned and the system is called "no-hub".

Here is a link that might be useful: no-hub images
cookingofjoy
11 years ago
last modified: 9 years ago
On a walk through before purchasing our 1912 home, when the toilet upstairs was flushed, there was water running down the stack to the basement. They opened the wall to see how bad it was, and there were two or three big corroded holes (like 6"x12-18"), on the second floor section. We were told that it was probably due to the second floor bath not being used for years (like 10+ years). I didn't end up seeing any of the first floor section to know its condition. It ended up that the seller paid for replacement with pvc. It sounds like ours was quite a bit worse than yours though, it was definitely more than a crack!
brickeyee
11 years ago
last modified: 9 years ago
"It ended up that the seller paid for replacement with pvc. "

Always go for the cheap repair.

Cast Iron Stack Crack--Why?

rwiegand

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