There are plenty of pond building guides, especially older published sources, that claim flexible pond liners are unnecessary. Some instructions claim that compacted clay soil is more than sufficient to hold water permanently, while others recommend the use of imported materials like bentonite clay. These materials might sound natural, but they tend to backfire on the pond owner and lead to large-scale leaking that’s hard to detect or contain. Bentonite clay products also tend to cost far more than expected, not producing significant savings over buying a reliable geomembrane liner. All these reasons, and more, should convince you to avoid clay liners and soil-sealed pond designs.
Seepage
None of the natural lining options, even advanced methods that combine polymers with clay products, can compare to geomembranes when it comes to seepage control. Seepage is the slow loss of liquids through a material due to the drainage effect between the particles of soil or other materials. Even the smoothest clay soils still have plenty of gaps between their particles. Bentonite clay forms a thicker layer when piled on a foot thick or more, but it’s still prone to seepage over time. In comparison, geomembrane liners made from materials like reinforced polyethylene are far more impermeable. There’s little loss of water over time, as long as leaks are prevented with careful seam sealing. A pond with an impermeable liner can stay filled for years, even with the constant water loss at the surface due to evaporation.
Disturbance from Roots and Animals
All liner materials can eventually become damaged by the aggressive growth of tree roots or animals burrowing around the pond. However, geomembranes with a reinforced design are far more durable and resistant to leaking than basic clay or Bentonite liners. Layers of clay are easily disturbed by anything from a sinking tree trunk to a digging animal. It only takes one spot of disturbed clay or broken natural liner material to create leaks throughout the bottom. In contrast, reinforced liners in particular are resistant to these disturbances. Even burrowing muskrats and raccoons often aren’t a problem when a heavy-duty pond liner is used. A durable liner lasts much longer without developing as many small leaks over time.
Lack of Conformity
One of the main reasons that clay-based and natural pond liners tend to leak is a lack of conformity. It’s also one thing that geomembrane liners excel at providing. Even with careful attention to detail and the right equipment, it’s harder than you think to get even compaction or a steady layer of clay over the surface. Every uneven area or missed spot during the lining process creates a new opportunity for leaking or seepage. Geomembrane liners are easily rolled out over the entire surface so that none of the pond’s bottom or sides are left uncovered. There’s also less of a chance of sliding along the edges of the pond where gravity causes the clay to settle unevenly over the sloped surface. Reinforced liners, in particular, are good at staying in place regardless of the steepness of a slope on a residential pond.
Constant Repair
Natural soils and clay liners both need regular attention to stay stable and well-refreshed. Compaction and settling slowly cause the material at the bottom of the pond to move and shift. In order to avoid eventual leak formation, most natural pond owners have to add new layers of bentonite clay every one to three years. Waiting even five years before adding a new layer of clay can result in a leaking pond that’s harder to repair. Natural ponds are often damaged by the process of maintenance and repair as well, since the banks aren’t reinforced by the addition of a liner.
High Cost
The amount of clay needed to coat the pond with 12 to 16 inches of fresh material can cost thousands of dollars. Geomembrane liners can last decades before needed repair or replacement, making them far more affordable in the long run. Don’t underestimate the costs of dealing with leaking clay liners on a regular basis compared to relying on a long lasting, cost effective, durable, flexible liner. Include labor for accessing the pond, draining and dredging it, and applying the new liner materials as well. Since residential ponds rarely have big budgets to keep them maintained, it’s best not to turn to a liner material that needs refreshment every few years. Once you factor out the cost of installation over the lifespan of the pond, you’re likely to find that geomembrane liners are far more affordable.
Lack of Leak Detection
It’s difficult to impossible to determine if a pond is really leaking with a clay liner. The ground may be soggy around the edges to indicate water loss, but there’s little opportunity to track down the precise source of the leak and stop it. When the pond owner invests in a reliable, flexible, liner material, they have multiple options for professional leak detection. Electrical charge testing can help pinpoint leaks in a geomembrane liner while the pond is still full of water, while vacuum testing ensures that a new or exposed liner isn’t suffering from any leaks. All you can do if you suspect a leak in an existing pond, with a natural liner, is keep adding more clay to try and stop the water loss. Draining the pond and putting in a flexible geomembrane liner is usually the best option at that point rather than continuing to add more and more Bentonite powder.
Difficulty Dredging and Cleaning
Clay liners blend in naturally with the sludge that accumulates along the bottom of a pond. When it comes time to dredge the pond to remove this sludge, the clay liner is usually punctured or removed along with it. Even the most skilled operators of dredging equipment tend to damage the bottom of ponds lined only with dirt or clay. It’s simply too hard to tell where one layer of material ends and the next begins. Flexible liners are much tougher, especially reinforced geomembrane materials like RPE. It’s easier to dredge all the way to the liner without damaging it since there’s a clearer division between the bottom of the pond and the sludge layer.
Availability
Finally, Bentonite clay products can vary in availability in certain parts of the country. If the material is not widely used in your area, it may require costly shipping to be delivered from another region. Flexible geomembranes are much more likely to be available locally and easier to ship long distances if necessary. The material is easily compressed for transportation, so it takes up less space while remaining easy to unroll for installation. In contrast, Bentonite powders and pellets are heavy and bulky to ship, increasing total costs and limiting availability.
Don’t gamble with natural clay pond liner products, even for small backyard projects. They’re not worth the cost and effort for the high risk of leaks developing within the first few years of use. Instead, choose a reliable liner product from us here at BTL Liners. Our liners are affordable for residential ponds of all sizes and types, making them the best choice for long-lasting water features. Explore our selection of fish-safe liners if you’re planning a koi pond or fishing hole for your backyard.
