Sodium Bentonite Pond Sealant
The simplest, most economical, and most environmentally friendly way to seal a pond is by applying sodium bentonite. Bentonite pond sealer, a natural clay product, chemically attracts to itself and swells up to 20 times its dry size when moistened. Expanded bentonite forms an impermeable gel seal which makes an excellent pond sealant. Sodium Bentonite is environmentally safe and does not affect the water, livestock, or wildlife. When properly applied, it will not harm fish. For these qualities, sodium bentonite also makes an excellent liner for new pond construction. Safe, natural, relatively inexpensive, the watertight membrane that may be your best answer to sealing your pond is sodium bentonite clay!
When sealing a leaking pond to prevent water loss through seepage, sodium bentonite can be applied directly to the soil in the pond bottom or it can be sprinkled on the surface of the water and allowed to settle to the bottom. There are three basic methods: the blanket method, the mixed blanket method and the sprinkle method. Sodium bentonite is easily applied. In the case of small ponds, it can be applied with simple hand tools and for larger ponds, with ordinary farm equipment.
The Blanket Method
The blanket method is usually the most effective method for sealing leaking ponds with bentonite. However, more care is required during it’s application. Pond Sealer, a mixture of powder and granular sodium bentonite, is best suited for this method unless working in an extremely windy area, in which case, we would recommended Granular Seal.
The first step is to prepare the surface to be sealed. Remove all rocks, trash, and vegetation, including trees and roots. Roots left in the ground will decay over time, leaving the potential for future leakage problems. Remove the top 4″ – 6″ of the soil from the pond bottom. Fill any deep holes or crevices with a uniform mixture of one part bentonite to five parts soil. Then smooth the area by roller or drag.
Cover the area with the prescribed amount of sodium bentonite. It is very important that the bentonite layer is even and that there are no bare or thin spots. This will ensure complete coverage and a water tight seal. After the bentonite has been spread as evenly as possible, carefully replace the 4 to 6 inches of soil that was removed earlier. While spreading the soil, be certain not to disturb the bentonite layer, as this could leave bare spots which could allow water loss to continue. If livestock will have access to the pond, the cover coat must be thicker than 4 inches. In this case, a top layer of gravel would be best to protect against puncture by cattle hooves.
Finally, compact the pond bottom by rolling or tamping. Use care when filling the pond. A gentle water flow is recommended to prevent erosion of the soil and bentonite layers during this final phase. It may take several days for the bentonite to reach the point of full saturation and fill the voids in the underlying soil.
Mixed Blanket Method
Begin by preparing the surface to be sealed. Remove all rocks, trash, and vegetation, including trees and roots. Roots left in the ground will decay over time, which leaves the potential for future leakage problems. If the soil is dry, lightly moisten it, then plow, disc or till the bottom of the pond 4″ – 12″ deep, then roll or drag the surface until it is smooth. This initial plowing and blending of the soil will assure consistency of the soil throughout the bottom of the pond before the bentonite is mixed into it. When this is complete, apply the prescribed amount of sodium bentonite. We recommend Pond Sealer, a mixture of powder and granular sodium bentonite for this application.
The bentonite can be spread by several different methods, however, we recommend a fertilizer or seed spreader to ensure even spreading. Mix the bentonite with the top 4″ – 12″ of soil by discing, tilling, or by hand raking. It is extremely important for the bentonite to be mixed uniformly with the soil. To ensure that no bare or thin spots will be left, we recommend multiple passes over the area. If livestock will have access to the pond, the cover coat must be thicker than 4 inches. In this case, a top
layer of gravel would be best to protect against puncture by cattle hooves.
Finally, compact the pond bottom by rolling or tamping. Use care when filling the pond. A gentle water flow is recommended to prevent erosion of the soil/bentonite layer during this final phase. It may take several days for the bentonite to reach the point of full saturation and fill the voids in the soil.
The Sprinkle Method
The sprinkle method is recommended only when it is not feasible to drain the existing pond or in cases of isolated leaks when a spot treatment may be a possible alternative. This method is less effective than the other two methods for several reasons: Uniform and accurate placement of the bentonite is difficult; the pond bottom may include debris such as trash, vegetation, logs, rocks, etc., which may prevent sufficient coverage. If the bottom of the pond can be cleared, this method has greater chances of providing a good seal.
The granular grade of bentonite, “Granular Seal,” is best suited for this method of sealing leaking ponds. The granular bentonite should be used when using the sprinkle method because the particles are large enough to sink to the bottom, while finer particles cloud the water and stay in suspension. Begin by simply sprinkling the prescribed amount of granular bentonite (Granular Seal) on the water surface and allow it to fall into place. The granular bentonite particles will sink to the bottom of the pond or be drawn into porous areas where they will swell and reduce the seepage rate.
Testing Your Soil
The purpose of this test is to find out the type of soil at the bottom the pond, and thus, to determine the amount of sodium bentonite needed to seal the pond.
Perforate the bottom of a can, a pail, or a drum and put two inches of gravel in the bottom. Take a sample of soil from the area to be treated. Be sure that the sample used is representative of the entire pond bottom. Cover the gravel with 6″ of the sampled soil. Tamp the soil, then elevate the container so that the bottom is open to drain before filling the container with water. Once the container is filled with water, observe the results. Based on the result, repeat the procedure using the chosen application method and the recommended bentonite dosage to seal the pond. If the test doesn’t seal off the leak as desired, repeat the procedure with a slight increase of bentonite dosage on each test until the leak stops.
Keep in mind that an additional 25% to 50% more bentonite could be needed on large scale projects to allow for greater water depths (water pressure) in the pond.
Application
Pond Sealer can be applied directly to the soil in the bottom of the lake or pond. If conditions necessitate sprinkling the bentonite through water, to the bottom, we recommend using Granular Seal, which contains no powder. Treatment is usually more effective if the bentonite is applied directly to the soil. The sprinkle method is recommended only when it is impractical to drain the water from the area to be treated.
| Soil Type | lbs/sqft |
|---|---|
| Clay | 2 |
| Sandy Silt | 3 |
| Silty Sand | 3.0 |
| Clean Sand | 4.0 |
| Rock or Gravel | 5.0 |
Add a pound if deeper than 8 ft, 2# if deeper than 16ft
Packaging
Available in 50 lb polyethylene bags, 3,000 lbs bulk bags and bulk loads.
PERMEABILITY 1.9 X 10(-9) cm/sec If the size of the pond is known and the type of soil is available, the chart above gives a good estimate on the amount of bentonite needed to seal the pond. Performing a soil test is another good way to estimate. You can perform the soil test yourself or contact your local conservation service for a free test.