What Are Cast-Iron Drains?

Before plastic plumbing such as ABS (Acrylonitrile butadiene styrene) and PVC (Polyvinyl chloride) in the 70’s, cast-iron was a commonly used material for waste drain pipes installed in San Antonio, TX homes. Mankind has experimented with all types of materials since the first engineers created waste drainage: the romans used carved stones and even lead. In the early 20th century, a product called “Orangeburg” pipe was used. Orangeburg, named for the town it was primarily manufactured in, was a combination of wood-pulp and tar that was formed into a pipe. After less than 15 years, these pipes collapsed abruptly, as one would imagine pipes made of wood pulp would do.

Cast-iron, the same material commonly used for your kitchen skillets, was chosen for drain pipes because of irons abundance and relative affordability, as well as its ductility, or ability to molded and shaped. Cast iron drains were labor intensive to install and the pipes were joined typically by inserting one end into the other, and sometimes melting tin or lead inside the joint to seal it. Cast iron was thought to last for decades, and in some cases, the pipes have in fact lasted for decades, but not without significant deteiroration. And that’s the problem: if you have cast-iron drains installed in your home, they have deteriorated and will eventually need to be replaced.


The Problems with Cast-Iron Drains:

cracked cast-iron drains

Cast iron is just that: iron, and it rusts. It rusts from the inside where water is in direct contact and on the outside as the finish of the pipe exterior wears out and oxidizes. The inside is subjected to water flow as well as waste and chemicals that sometimes accelerate the corrosion of the pipe. The pipe will eventually deteriorate, and may collapse in on itself or allow for the entry of dirt, more moisture, or plant roots. Ground movement or soil movement depending on location will also contribute to the shifting of the unsealed pipes, allowing leakages.

Plant roots are the biggest enemy of cast iron drains. Plant roots search underground for sources of water and nutrients, of which the waste drains have both. Because the joints of the cast iron pipes are often only fitted together with compression and are commonly not sealed, it doesn’t take much for the tree roots to penetrate the pipe and begin growing inside. This is the most common cause of cast iron drain blockages. Once inside, the tree root continues to develop, using the water and nutrients found in the pipe to further grow, eventually blocking the drain. This process can take years and may not be noticed until the problem has become severe and blockages start occuring constantly. The tree roots can be cut by a plumber with a rotary tool, but this tool can often cause more damage to the pipes and is only a temporary solution; further and more expensive solutions will have to be taken eventually.

extremely deteriorated cast-iron drains

When leaks occur at cast iron drains, these leaks can go unnoticed for years, as unlike a water supply pipe leak, you’re not going to see high-water bills because of a drain leak. When this happens, water begins to saturate the soil in the area. Saturated soil, depending on the soil’s composition, can expand, hydraulically lifting your concrete foundation in some areas. We commonly find that a leaking drains underneath a slab are the cause of some excessive foundation movement that we observe in a home.


How Do I Know if I Have Cast Iron Drains?


Exterior Visual Observeration

First, look around your home for plumbing cleanouts. Cleanouts are areas, typically around the exterior perimeter of the home, on an exterior wall, or under a kitchen sink where accessible connections directly into your drain system are located so that if a clog develops in your drain system (for any number of potential reasons), a plumber can insert a tool to clean the clog out. When you locate a cleanout, look at the material the pipe is made out of: is it iron or metal? That’s cast iron. Is it a white cap or white pipe? If the pipe is made of a white plastic, it’s PVC. Sometimes we will find cast iron drains that have a PVC caps inserted into them; these drains are still cast iron.


Sewer Camera Inspection

The second option is to hire a qualified professional to perform a sewer camera inspection. A sewer camera inspection involves a professional inserting a waterproof camera that is attached to a long, semi-ridge cable down your drain lines in order to observe the conditions inside the drain pipe. This is the most effective way to observe the condition of the pipes, including identifing any blockages, and sagging or “bellies” in the pipes, siginificant deterioation, and sometimes leak points such as the joints.

Sewer camera inspections required a plumber’s license in the State of Texas until 2020, at which point a licensed is no longer required to perform them. Still, you should make sure that the professional performing the sewer camera inspection is qualified for the job.


What are the Solutions to Cast Iron Drains?

If you are worried about buying a home with cast iron drains, my first solution is simple: don’t buy a house built before 1980. Doing this should dramatically reduce the potential for inhereting a home with significant drain issues.


Cast Iron Drain Replacement

For everyone else, correction of cast iron drains can get expensive, although there are different options available. The most common is a full-replacement of the cast iron drains. If the home is really old and has a pier and beam / raised foundation, this is a less expensive job than if the home was on a slab foundation, as a sizable portion of the cast iron drains will be accessible from the crawlspace.

If you have a slab foundation, drain replacement is an ordeal. Typical replacement will involve digging a trench from the drainline connection from the city to where the drain enters the home under the foundation. You heard that right, somebody will have to tunnel under the foundation of your home. This can cause problems itself and is dangerous work. The cost per foot of digging under a foundation typically starts at $200 per foot, but can go higher depending on the circumstances of the home and the soil. After excavation, the old drain is removed and modern PVC drains are installed in their place. While I’m not a plumber and I don’t do this type of work for a living, in San Antonio, TX, I’ve never heard of a drain replacement costing less than $15,000, so use that number as a minimum starting point.


Trenchless Pipe Repair

Some very smart people came up with the idea of repairing cast iron drains without having to dig up the pipes. This process involves inserting an epoxy lining inside the drain pipes with some very expensive machinery so that, although the old cast iron pipes are still present, their is a fresh, smoooth walled lining inside the pipes where waste and water can flow into and roots are less likely to penetrate. Before you get excited, this isn’t any cheaper than drain replacement; these machines cost hundreds of thousands of dollars. No, the benefit of this system is that it doesn’t cause damage to other components of your home such as the foundation as you aren’t tunneling under your home. It also doesn’t require you to vacate the home for as long as a drain replacement may take, instead taking only 2-3 days to prep the pipe and insert the liner. Before commiting to cast iron drain replacement, consider shopping around about slip-liner repair.



16400 Henderson Pass, STE 517
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