Should You Repair or Replace Cast Iron Sewer Pipes?

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If you have a sewer leak or leaks under the concrete slab of your home’s foundation, it’s possible it could cause cracks in your walls or foundation, sloping floors, or more.

And once you find out you have a sewer leak, most likely it’s been there for a significant amount of time. So it’s in your best interest to take action to prevent any possible or further structural damage to your house.

But if your system is made of cast iron the question becomes: Should you repair the leaks? Or go ahead and replace the pipes?

Repair or Replace Under Slab Cast Iron Pipes

Cast iron pipe was designed to last 50 years. Here at In-House plumbing, we’ve seen a 20-year-old pipe that was no good and 50 year-old-pipe that was fine.

The truth is there are so many variables and factors that contribute to the deterioration of cast iron pipe. And while there’s no way to know when your pipe will go bad, there is no doubt that they will go bad.

The last houses constructed with cast iron pipe in DFW were built around 1986. However, many houses in the area were built using PVC pipe even as far back as the late 1970s.

With this in mind, any cast iron pipe installed under the slab will require replacing in the next 5 to 20 years. If not sooner.

It is important to note that any time an under slab cast iron sewer pipe is repaired, meaning just the spots with leaks are repaired, what was just one problem or leak will be at least 2 problems in the same spot in the future.

The cast iron on each side of the repair will go bad e.g. crumble, crack, break, leak, etc. That’s just the nature of the material. As the metal repeatedly comes into contact with the wastewater that runs through it, it deteriorates.

Full or Partial Replacement?

So with cast iron sewer pipes, especially older pipes, it doesn’t make sense to locate or repair the leak or leaks.

Now we understand not everyone can afford to replace all of the cast iron pipes under a slab at once. This is why some might opt for the repair instead.

But affordability, or lack thereof, makes it that much more important to consider all your options. It’s especially important to take a long-term view rather than an immediate one.

Sometimes it is possible to replace part of the pipe now and some of it later. And sometimes there’s another option altogether.

A Real Life Example

A good example of this is a job we had in Mesquite, TX. The house was 3 bedrooms and 2 baths. At some point in the past, another company tunneled 12 feet starting from the outside of the house at the kitchen sink which was touching the outside wall on the right side when facing the house.

The main sewer line went to the front of the house and both bathrooms touched the left outside wall. The kitchen sink line was basically a straight line all the way across the house to the bathrooms. The washing machine was at the back center of the house by the garage. And its sewer line tee’d into the kitchen line about 20 feet or so from the kitchen sink.

The previous company tunneled the 12 feet from the outside to replace 12 feet of the deteriorated cast iron kitchen line. But that’s all that company did.

Sidenote: If part of the line is deteriorated, how long do you think it will be before the rest of the pipe that was made and installed at the same time becomes deteriorated (if it’s not already)?

They charged the homeowner about $6000 to replace the 12 feet of sewer line.

What We Found

When we came in several years later, we found that there were not only more problems on the remaining 40 feet or so of the kitchen and washer line but at the bathrooms as well.

But what made things worse for the homeowners when we told them what we found during our inspection was when we told them our method for solving their problem. We suggested rerouting the pipe from the kitchen sink line underground into a trench outside of the house — not under the house under the slab. This put the pipe in the front yard instead.

Meaning? The $6000 they paid the previous company and the 12 feet of new pipe was a complete waste. With our repair plan that pipe was abandoned.

Why ReRoute the Sewer Line?

So why abandon the new pipe replaced by the previous company?

Replacing the remaining pipe meant re-tunneling the 12 feet the previous plumber tunneled. AND also meant a lot more tunneling. Not to mention the need to punch holes inside the house and tunneling from those holes for a total under slab excavation of 28 feet or more.

This option costs 3 times more than our suggested plan.

Our suggestion to reroute was far less expensive. And by rerouting this part of the sewer line outside of the house instead of under it, if there ever is a problem in the future, fixing it is easier and cheaper. Future repairs to this new portion of the pipe won’t require expensive tunneling or punching holes in the slab.

So if the original plumber had just rerouted the kitchen line, it no doubt would have cost less than $6000. And it would have eliminated the need for us to reroute it when we did which cost the customer more in the long run.

Then we could have concentrated on the new problems and addressed those for the long term. The owners could have gradually over time replaced the pipe as each part became necessary to replace.

A Trustworthy Plumbing Company

It is important to note not every house is like this one. But looking at each house and problem with long-term solutions in mind is possible and necessary in every situation.

This is why it’s important to find a reliable plumber or plumbing company whose motives are to help you not themselves.

In the example we just discussed, the former contractor did what was best for himself at the time. He did more work for more cost and left himself in a position to do even more work later. Because there was no doubt going to be more problems.

It’s highly likely this contractor believes in the “tunnel only no matter what’ philosophy. So if he tunnels 12 of the 40 feet knowing all 40 has to be done at some point, he can do the 12 now and all 40 in the future. Not to mention the original 12 again if he uses the same access hole at the kitchen sink.

Our Recommendation

Based on the fact that all cast iron sewer pipes will need to be replaced, we strongly recommend that cast iron pipe under a concrete slab be replaced and not repaired.

In fact, we have decided we will no longer locate or spot repair any sewer leaks on a cast iron system. We believe locating or repair sewer leaks on a cast iron system is a waste of time and money for the homeowner.

However, we always look at all possibilities from a long-term point of view based on your specific needs and budget.

If you have any questions, comments, concerns or want a free no obligation estimate, give us a call at 972-494-1750. Or email us at

In-House Plumbing Company

Get Sensible Solutions Today

Say goodbye to water or sewer leak issues, especially ones under your foundation, by putting our plumbing company to work for you. We offer timely, sensible solutions and restore peace of mind without significantly affecting your property or budget. Contact In-House Plumbing Company today to schedule an appointment.