Plastic vs. Concrete Septic Tanks: Pros, Cons, & Differences

If your home doesn’t have access to your town’s public sewer system, the only way to remove the wastewater you produce is via a septic system and septic tank. If you’re in the market for a new septic tank, one of the first decisions you must make is what type of material your tank will be constructed from.

The two primary materials used are concrete and plastic, both of which have advantages and disadvantages. Keep reading to discover the similarities and differences between plastic and concrete septic tanks.

Plastic Septic Tanks Overview

Purchase Cost

If you’re on a strict budget and doing everything possible to save money, a plastic septic tank will be a better choice than concrete. The reason is simple; plastic septic tanks are considerably less expensive than concrete tanks. Also, at the end of its useful life, removing and disposing of a plastic tank is easier and less costly than removing one made of concrete.

Installation Cost

Because plastic septic tanks are lighter and less complex than concrete, their installation costs are usually less and, often, significantly less. Installing a plastic septic tank is far less disruptive to the ground around your home. Also, the cost of transporting a plastic septic tank to your home is less than a concrete tank as they’re easier to load and unload and weigh significantly less. Lastly, once at your home, moving a plastic septic tank into place takes less time, effort, and heavy machinery than concrete.

Durability

Durability is one factor where a plastic septic tank doesn’t compare favorably to one made from concrete. Plastic septic tanks, on average, last about 10 years less than concrete. Also, once installed in the ground, plastic tanks are more susceptible to damage from tree roots, vibration in the soil, and other factors.

One critical difference concerns where the septic tank will sit in your yard. For example, if it is placed where your car or truck will roll over it regularly, a plastic tank is not a good choice as it can’t handle the extra weight as well as concrete can.

Soil Acidity

Experts suggest checking the pH of your soil before deciding which type of septic tank to purchase. The reason is that acidic soil can be problematic for concrete. However, a plastic septic tank will have no problem with acidic soil and thus is a better choice and will have fewer potential problems.

Floating and Shifting

One primary drawback plastic septic tanks have is that, since they’re lightweight, if the groundwater in your yard increases dramatically, they can “float,” which in turn can cause the tank to shift out of place and its lines to disconnect or rupture. Floating could cause significant damage and require expensive repairs to a plastic septic tank and its connecting lines.

Maintenance

Plastic septic tanks need slightly more maintenance than concrete tanks, although they hold up better to corrosion as they are highly rust-resistant. Plastic tanks are also less prone to cracking.

Concrete Septic Tanks Overview

Purchase Cost

While the difference in cost isn’t huge, concrete septic tanks cost several hundred dollars more than plastic tanks. Delivering a concrete septic tank is also more expensive due to its immense weight and the heavy equipment required to put it in place. These factors can increase your installation costs even more. Concrete is also more difficult to repair and, at the end of its useful life, it’s more expensive to remove and dispose of, increasing its cost.

Installation Cost

The installation of a concrete septic tank is more expensive than a plastic tank due to its extra weight and bulkiness and because concrete tanks employ a more complex plumbing system. Depending on where you live, transporting a concrete tank may be difficult or even impossible. Transportation costs can be influenced based on how remote your home is as well as the roads leading to it.

Durability

Regarding durability, a concrete septic tank is the better choice. Concrete tanks last about 25% longer than plastic tanks because they aren’t as susceptible to things like tree roots, the soil shifting, and weight shifts. Also, concrete can handle cars and trucks driving overhead, so installing them under a driveway is not a problem. Lastly, accidentally punching a hole in a concrete septic tank is almost impossible, whereas it’s relatively easy with a plastic septic tank.

Soil Acidity

If the soil around your home is highly acidic, experts warn against using a concrete septic tank since it is more susceptible to acidity and, over the years, will begin to deteriorate and crumble.

Floating and Shifting

While plastic septic tanks are susceptible to floating and shifting, concrete tanks are not. That’s primarily due to their immense weight, which will keep them in place if the water level in the ground around your home increases dramatically. In short, a concrete septic tank will rarely float or shift position, even under the heaviest of rains or flooding situations.

Maintenance

While regular maintenance on a concrete septic tank is less than on a plastic tank, they are more likely to crack. Cracking can be even more of a problem if the concrete used was improperly mixed or cured. Concrete tanks are also prone to corrosion and rust, while plastic tanks are not. Lastly, if your concrete tank needs repairs, they can be significantly more costly than repairing a plastic tank.

Other Factors to Consider when Choosing a Septic Tank

Besides the advantages and disadvantages we discussed above, there are several other factors to consider when choosing a septic tank for your home.

Which Septic Tank is More Environmentally Friendly?

One concern many homeowners have today is being friendly to the environment, especially around their homes. It’s worth noting that concrete is non-toxic, made from natural components, and, for those reasons, is safe for the environment. Concrete will not affect groundwater and doesn’t leech.

Plastic septic tanks, if maintained correctly, are also environmentally safe. However, unlike concrete, if they aren’t maintained well, plastic septic tanks can pose a risk to ground and surface water. That’s because if the groundwater increases dramatically, a plastic tank can float and shift, rupturing the lines and spilling sewage and other effluents underground and above ground.

Damage during the Installation Process

While this isn’t a disadvantage of plastic septic tanks per se, the fact is that, when being installed, plastic tanks can easily be damaged by an inexperienced crew. Statistically, the biggest cause of plastic septic tank problems and breakdowns is damage that occurs when they’re being installed. Installing a concrete septic tank is a more extensive process, but the chance of damage during installation is much lower than with plastic.

Septic Tank Collapse when Emptied

Although a relatively rare occurrence, plastic septic tanks are prone to collapse when they’re being emptied, which can cause a big, expensive problem to fix. Concrete septic tanks are far less prone to collapse than plastic tanks when emptied. Indeed, experts state that concrete tanks, if they’ve been maintained well, are almost impossible to collapse. Even in perfect condition, plastic tanks can collapse when emptied due to the weight of the soil surrounding them.

Anchoring a Septic Tank

Plastic septic tanks must be well-anchored to the ground where they are installed to prevent them from floating and shifting if groundwater swells. Anchoring, however, isn’t necessary with concrete tanks as they weigh significantly more than plastic and won’t float or shift due to changing groundwater levels. The extra time and cost to anchor a plastic septic tank will often increase their installation cost, sometimes significantly.

Septic Tank Removal

Depending on your state, you may be required to remove a septic tank that’s damaged or is no longer in use. Removing a plastic septic tank is usually far easier and less expensive than a concrete septic tank. Also, disposing of the concrete used to make a concrete septic tank can be difficult depending on where you live and will typically involve a disposal cost.

Your Home’s Location Is a Big Factor

As we’ve seen, there is a significant weight difference between a plastic and concrete septic tank. This makes transporting a concrete septic tank more complicated than a plastic tank. Also, delivering a concrete tank to your home may be extremely difficult, depending on where you live. For example, if you live in a remote, wooded area with dirt roads, approaching your home with a heavy truck and septic tank might be impossible.

The same can be said for professional maintenance of your septic tank. The further you are from a city or town, the more it will cost to have a professional sewer maintenance company travel to your home and provide their services. Also, if the roads and terrain are difficult to travel, a professional sewer maintenance company might charge more to come out to your home.

Labor Costs

Although labor costs usually don’t differ significantly when installing a concrete or plastic septic tank, they might. For example, if you live in a remote area, the labor cost to install your new septic tank might be much higher than if you live near a city or town. Also, the state you live in might have higher or lower labor costs, so determining those costs beforehand is critical. According to experts, installing a septic tank is typically between 50 to 70% of the total project cost.

Legal Requirements

One significant factor that will affect your decision when purchasing a septic tank is the laws in your state. As we mentioned, some US states allow plastic septic tanks, and some do not. However, all US states allow concrete septic tanks. For this reason, you must check your state and local laws to ensure that the septic tank you choose is permitted.

Effluent Levels

One last factor to consider when choosing between a concrete or plastic septic tank is that plastic septic tanks can’t handle as much effluent as a concrete tank. That’s because, in a septic tank, the sludge (solids), scum (lightweight solids), and effluent (water) must balance properly.

If your plastic septic tank was suddenly overwhelmed by effluent, it could overflow, causing contamination of the ground and surface water. Lower maximum effluent levels are the main reason that plastic septic tanks are more costly to maintain than concrete tanks.

Final Thoughts

Choosing between a plastic septic tank versus a concrete septic tank can often be difficult. Then again, the factors involved in your particular situation might make it much simpler to choose due to legal restrictions, soil conditions, environmental factors, the location of your home, and several others. As we’ve seen today, both concrete and plastic septic tanks have advantages and disadvantages. Hopefully, the data provided today will make your decision much easier. Whichever you choose, best of luck with your new septic tank.

• Related Read: Septic Tank vs Sewer: Which Is Better?

Featured Image Credit: (L) Hamik, Shutterstock | (R) DyziO, Shutterstock