When you flush your toilet or drain your sink, that water has to get from your home to the city sewer lines. It does that by draining down your pipes and traveling down your home’s main sewer line. All the water in your home leaves through the same mainline. If that pipe fails, the water has nowhere to go except back into your home.
That means it’s important for your sewer main line to be able to hold up under pressure. One of the biggest factors in whether it will last is the pipe's material. Home builders have used several different materials for sewer mainline over the years. Each one has benefits, and each one has its weaknesses. This post is going to go over 4 common mainline material types and what each one means for your home.
A common material from before and after World War II, cast iron can be strong and resilient. It depends on how well it was cast into shape, the quality of the iron, and its installation. When a crew did everything right, cast iron sewer mainlines from the 1960s have lasted for 60 years or more.
Cast iron does have its flaws. If the casting or installation was bad or the pipes used low-grade iron, they can crack or form bellies. They also have a unique weakness to static electricity. Static can build up from the constant flow of water, causing the cast iron to rust sooner than it should.
Vitrified clay comes from heating clay to change it into a glass-like structure. It was common in homes until the mid-1960s when builders started phasing it out. Heavy and durable, clay is also inert. That means it doesn’t react as much to chemicals in the soil as other materials might. It also means they resist the acidic nature of the sewer wastewater flowing through them.
Clay pipes are heavy, making it difficult to use pipes of any significant size. That means they had frequent joints along a sewer mainline. On top of that, those joints were often designed to be “dirt tight” instead of watertight. That meant larger gaps between pipes and more room for roots to worm into the joints. But as long as roots don’t penetrate the pipe, clay can be an effective option.
Also known as fiber conduit pipe, sheets of woven wood fibers make up Orangeburg. Manufacturers rolled the fibers up and sealed them with water-resistant adhesives and tar. It’s lightweight and easy to cut with standard wood saws. It was common during World War II because the war effort claimed other materials.
Orangeburg has a hard time withstanding the strain required long-term. The layers often separate, letting water leak out and roots work their way into the pipe. Many Orangeburg sewer mainlines collapse, requiring total replacement. A well-installed Orangeburg pipe with the right support can last longer. But any Orangeburg pipe risks large-scale failure.
Modern homes almost exclusively use plastic pipes for sewer mainline pipes. They’re non-corrosive, non-reactive, lightweight, and strong. They can have a much tighter fit than other materials. As long as the plumbers install it well, a plastic sewer line should last 100 years without any attention.
The installation is key for a plastic pipe. If the ground isn’t prepared right or the pipes aren’t sealed well enough, a plastic line can form a belly or crack. That can either allow water and waste to collect in one location until it backs up, or let roots invade the pipe. But a well-installed plastic pipe should never have any of these issues.
