How to Recognize and Deal with Corrosion in Your Cast Iron Sewer Main

If your home was built in the 1970s or later, there's a good chance your main sewer line is made from cast iron. Iron sewer lines have a lot of advantages over the clay lines that were used prior to the 1970s. They're less susceptible to tree root growth and less likely to be crushed or bent by shifting soil or freezing/thawing cycles. However, there is one issue that you should be aware of if you have a cast iron sewer main: corrosion.

What is corrosion and what problems does it cause?

The main type of corrosion that occurs in a cast iron sewer main is rust. However, you can also get deposits of other minerals that settle out of your water as it washes through the pipe.

The issue is not really the corrosion itself; the corrosion layer stays rather thin. Rather, the problem is that the corrosion develops a roughened texture and begins to grab onto items like toilet paper, feminine hygiene products, and other solids that make their way through the sewer pipe. Over time, the clog can grow, obstructing the line. This can lead to a number of symptoms including:

  • sewage backups in your home. You may notice raw sewage gurgling up into sinks, tubs, and toilets.
  • smelly, sewage odors coming from your drains.
  • slow drains that operate at a trickle.
  • toilets that don't flush completely.

What should you do if you think your main sewer line may be corroding?

This is not really an issue you can address on your own, so a call to the plumber is in order. When they arrive, they will likely start by looking over the rest of your drain pipes to ensure that the sewage backups, odors, and other problems are not caused by a blockage in a smaller pipe.

If no smaller blockages are found, the plumber can send a camera down into your main sewer line. The camera allows them to see, in real time, how much corrosion has built up inside your pipe and whether a clog has also begun to form.

Note that even with a cast iron pipe, it is possible that the issue is that tree roots are growing into the pipe and contributing to the problem. If tree roots are discovered, your plumber can use a rotating blade to cut them away. He or she may also insert a special herbicide into the pipe to keep the tree roots at bay. In the long-term, removing the tree that's too blame will be important.

How will your plumber remove the corrosion?

If corrosion is, in fact, to blame for your sewer issues, your plumber can use a process called pressure jet cleaning to remove the corrosion and associated clog material. This process involves shooting water at the sides of the pipe at a high speed.

How can you prevent the corrosion issue from coming back?

Once corrosion has been diagnosed in your main sewer line, you'll typically want to have your plumber come back every year or two to re-treat the line with the pressurized water jet. There are also a few measures you can take at home to keep the problem from recurring:

  • Avoid using chemical drain cleaners, as these tend to enhance corrosion.
  • Do not flush feminine hygiene products down the toilet since they're more likely to get caught on corrosion and contribute to clog formation.
  • Keep baskets in your drain to prevent hair from rinsing down into the sewer line.

The older your cast iron sewer line, the more likely it is to develop corrosion. If your home has been around for a few decades, it's not a bad idea to have a plumbing contractor come look over your sewer main so you have a better idea of its condition. 


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