Examining Drain Clog Culprits

Examining Drain Clog Culprits

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Here’s a look at the common ways different types of pipe clog.

Terracotta sewer pipe

Terracotta is famous for having two major issues — root intrusions and pipe settling. No form of mechanical connection or seal was applied to terracotta joints until the invention of the rubber slide joint. Therefore, the settlement of one joint more than the next is widespread. In addition, the pipe settlement and separations allow roots to force their way into the pipe, finding nutrients from the waste.

The most common issue with terracotta piping is root infiltration. This is by far the biggest moneymaker in the world of drain cleaning. It wreaks havoc of all sorts and varieties. Once roots enter a sewer system, they may break every joint and migrate downstream and upstream, destroying each joint as they grow. Depending on the type of roots, they will also fill up the pipe to the point of 100% compaction. Different types of roots will have different growth rates and different densities. Sometimes, very thick-rooted trees will have a few thick roots that grow, making them almost impossible to cut down with a rod machine or jetter quickly. Other times minimal but very dense root systems such as red maples are strong enough to withstand root cutters because they are unbelievably strong when drenched and together, similar to the strength of a wet shirt — both flexible and robust.

These are the two most common issues with terracotta piping. With that said, settling or breaking of terracotta due to roots causes a wide variety of additional problems. At times, the rookie technician may think that these secondary offenses are the main reason a line has clogged. For example, if a few sections of terracotta settle and sink underground more than the pipe has settled upstream and downstream, the dip or downward bend/sag will cause what plumbers call a "belly." A belly will allow any greywater to pass through, but toilet paper and waste will slowly build up like a dam causing a soft clog.

A soft clog is when no foreign object or pipe break is causing the backup but rather a combination of waste and toilet paper. The rookie might open the drain, pull back toilet paper, and conclude that it was just a "paper stoppage" when a belly actually caused the paper stoppage in the line. Suppose the belly in the line is left without being adequately repaired. In that case, the stoppage issue will become recurring, and a nuisance will result in a tremendous number of callbacks, an angry customer, and maybe no repeat business from that customer.

Bellies in terracotta lines will cause all kinds of secondary problems — kitchen grease collecting in a belly, soft clogs accumulating, soap scum buildup, hardened and glazed material deposits, chemical deposit buildups, collection of debris that would normally continue downstream, and grease blockage from garbage disposals and scale buildup. Don’t pass off as a buildup that can be fixed with a rod machine or a jetter what in reality is something that requires a different solution.

Cast iron pipe

Cast iron piping was used primarily for in-house piping. It was heavy-duty and required the joints to be made using a combination of lead and oakum, or as plumbers call it, "pack and pour" joints. Cast iron was used even in the days of wooden piping as elbows and transition pieces, but later they were used commonly under-slab until the penetration was made through the foundation wall. The under-slab piping is referred to as "the building drain." After the cast iron piping was through the foundation wall, it would transition to terracotta piping from that point to the sewer main.

Cast iron only has one major issue — line denigration due to rotting. Over time, cast iron soil piping will rot. The rotting of cast iron pipes can cause all kinds of drain problems. The most common problem is the house drain piping, which no longer has a bottom. When the cast iron disintegrates, it's always because of the flow of water and waste through the same channels. Look at it as the Grand Canyon. If you have decades or centuries of flow through the same path of travel of a cast iron soil pipe, the bottom will eventually eat away, exposing the dirt or earth below. This surface is no longer smooth or uniform and can cause all kinds of backups. You can get a belly if the pipe is eaten away in one concentrated spot versus the other portions of the line. 

Also, suppose buildup occurs over some time, barnacles build up from the pipe's invert to the pipe's spring line, causing even more issues.

Opening main drain clogs through cast iron pipes is relatively easy once the equipment is in place and rodding or jetting begins. Still, backups will continue regardless until the line is either dug up, lined, or burst, depending on the circumstances.


One of the rare finds is Orangeburg sewer pipe. Orangeburg was a solution to steel supply shortages and sold as a root-proof piping material made of a mixture of tar and paper. It is black in color and ovals and crushes after decades of service. If you've never had your hands on Orangeburg before, it falls apart and easily chips away. Orangeburg should be replaced in its entirety if found.

Plastic pipe

There are many different types of plastic pipe, so I will spare the lecture on dimensional ratios, compositions and ratings. But, generally speaking, there are three problems you will face when a house has a clogged main drain with plastic sewer piping.

First, the piping could have been misinstalled and is therefore causing nuisance backups (no structured bedding material causing bellies, improper venting techniques causing sludging, and non-directional fittings or unapproved horizontal fitting arrangements such as sanitary tees, crosses, 90 elbows, etc.). Second, the pipe is too thin and is being crushed or oval. Third, the users of the drain are abusing the drain system by flushing things that shouldn't go down the drain.

About the Author: Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has over two decades of experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College.


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