Pre-Cast Concrete VS. Plastic Septic Tanks


Concrete durability and the availability of pre-cast concrete products often make concrete the easy answer for a new septic system install. Strength and structure for concrete construction is often the most cost-effective solution for septic tank installations for both newer and older homes.

Over 20 million households have a dirty little secret buried in their backyard. Not a mention of it is whispered in polite circles and the evening news ignores the subject entirely. It affects so many people, yet no one, even the ones that benefit the most, rarely give it a thought. What am I talking about? What’s the dirty little secret so many benefit from but refuse to acknowledge? Of course, I’m speaking of the mighty septic tank.

Once upon a time, someone decided that digging a hole every time he had to do the dirty was a lot of work and quite redundant. So Hal dug a big hole several feet deep and lined it with stones and bricks. It was set up so the entire family’s waste was directed into the pit, providing an easy and somewhat sanitary fix to a very unsanitary problem. There was only one downside to this great invention – it leaked like a sieve and polluted the groundwater they relied on for survival.

There had to be a better way, but Hal couldn’t think of it. Fortunately, someone else finally did and the septic tank was introduced. Of course, there was a learning curve in design and installation, but when the smoke cleared, there were two major types of septic tanks to choose from. One is a light, plastic receptacle that became popular due to the low cost, and the other, which is a heavier precast concrete design that is built like a tank.

Like most things in life, you get what you pay for. The initial low cost of the plastic septic tank is deceiving. It has some major flaws that should be considered before purchase. Take size, for example. Concrete tanks are larger, thus able to contain more sludge and wastewater. This means less pumping is required. Speaking of pumping, plastic septic tanks run the risk of collapsing during the pumping process. If a plastic tank collapses, a new tank will need to be installed. Ouch! No matter how many times you pump a concrete septic tank, it will never collapse.

Concrete septic tanks are the gold standard in the construction industry. Every state in the country welcomes the durability and sanitary characteristics concrete allows. Plastic tanks are often restricted in areas where groundwater contamination is a concern. Also, there’s the real concern that the plastic device will become damaged during the installation stage. If the damage is discovered during installation, it will need to be replaced. If the damage goes undetected, leaking could go on unabated, causing untold problems for the homeowner.

There are other ways a plastic septic tank can fail the homeowner. The sheer weight of the soil above can cause a plastic tank to collapse. A wayward vehicle that accidentally drives over the area where installed, can also achieve this effect. Also, plastic septic tanks usually have a lower effluent (wastewater and sludge) area than concrete ones and in the case of excessive rain or flooding, the tank can start to float from its original position. This can cause harm to existing plumbing and the tank itself.

Are there situations where plastic septic tanks are preferable to concrete?

Yes, there are several reasons to consider plastic over cement. Plastic tanks are easier to install and require less manpower and equipment during set-up. This results in lower installation costs. This ease of handling also allows plastic septic tanks to be installed in more remote regions and more quickly than cement ones. And let’s not forget that there are real initial cost-savings buying a plastic tank.

Are there downsides to cement tanks, other than cost?

Probably the biggest negative for cement tanks is the cost and installation. The incredible weight and size of the cement tanks make transportation a chore and installation requires heavy equipment and extensive manpower. Although sturdy, if damaged, a cement tank is very difficult to repair and often requires full replacement at a high cost.

Overall, cement septic tanks are considered the best choice under normal circumstances. If there is good access to the installation site and proper preparation, the process of installing a new unit is not hard. Dealing with the city regarding plans and permits is generally not a problem and although the process can be slow, the results are worth it. The durability is unmatched with cement and plumbing the unit is usually a snap.

Always consult a professional when determining between a plastic and a concrete septic tank. They can review your location and individual situation to help you determine which choice is right for you.

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