Clay sewer pipe is technically referred to as vitrified clay pipe. It has a strength and durability that far exceeds most people’s expectations. In many homeowners minds, and even to many licensed plumbers, clay sewer pipe is prone to root growth and to breaking prematurely. However that is far from the full truth and belies the fact that vitrified clay has been used for over four thousand years. There are still some ancient sewer systems that continue to function.
Environmentally speaking clay sewer pipe may be the ‘greenest‘ pipe produced. It is made from recycled clay and earthen clay, with other organic ingredients added. They are mixed together without using any chemicals, just water. After the mixture is formed into the desired length and width it is left to dry for about 24 hours. The term vitrified refers to the fact that the pipe has to be fired in a kiln for 50 hours. At that point it has a ceramic like finish and is completely impervious to water and most chemicals.
In almost all instances clay sewer pipe is not affected adversary by chemicals such as acid. Acids are found more than one would expect, such as in manufacturing. As an example ascorbic acid is as a preservative in many food products such as soft drinks and flavored ices. If acidic waste water is not treated and ph neutralized it can eat away cast iron pipe in a relatively short period of time. Clay sewer pipe on the other hand is unaffected by acids, even if waste water is left untreated. That is one of the reasons why clay drain lines installed thousands of years ago are still visible and functional in certain parts of the world. Clay sewer pipe is still the ideal material for many drain applications to this very day.
Modern clay drain pipe is carefully tested to over 2,000 pounds of water pressure, far exceeding any load it will bear when in use. A resin is carefully applied inside the hub and around the bald end of each piece of pipe to form a water-tight joint when connected together. One of clays disadvantages is that it is heavy. Its weight makes it more costly to transport and more difficult to handle than other drain pipe.
Clay is still routinely used in public sewer systems such as in NYC. It is typically encased in concrete or has a concrete cradle placed underneath it to provide added support and strength. For house sewer installations extra heavy cast iron and pvc has become the material most widely used across the U.S.A. Each different type of pipe material has unique properties that provides benefits over another. However it is widely held that extra heavy cast iron pipe is the product of choice. In a city like New York where trees are prevalent cast iron’s ability to withstand root infiltration is a great benefit. In addition it has a greater ability to withstand ground shifting during climate changes.