How to Stop Seal a Pond With Bentonite

Written by frank whittemore
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How to Stop Seal a Pond With Bentonite
A leaking pond can be resealed with bentonite. (Jupiterimages/ Images)

Seepage in an earthen pond can quickly drain the pond down to the bottom if left unchecked. Sodium bentonite, a special type of clay, has properties that can help to seal a pond. The clay expands greatly when wet, forming an impermeable layer between the water in the pond and the leak area. There are two primary methods for dealing with a leaking earthen pond using bentonite. The first is the sprinkle method, which may stop a leak before the pond drains. The other is the blanket method, which reseals a pond after it has completely drained.

Skill level:

Things you need

  • Sodium bentonite, granular

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  1. 1

    Sprinkle bentonite in the area where you suspect the leak to be. Use a granular bentonite that falls to the bottom quickly. Powdered bentonite will remain in suspension and will not sink or seal the leak.

  2. 2

    Work outward in a spiral from the suspected leak area. The leak will draw the bentonite into the porous area, where it will begin to swell. For clay soils, apply 1 to 1.5lbs. of bentonite for every square foot of coverage. For sandy silt or silty sand, use between 0.907 and 1.36kg. per square foot. For clean sand or gravel, use from 3.5 to 5lbs.

  3. 3

    Observe the leak over the next few days. As the bentonite swells, it will prevent water from escaping. Add more bentonite as needed to seal the leak.

  1. 1

    Remove any obstructions, such as roots, trees, rocks, or trash from the bottom of the pond once the water is gone and the pond bed has dried.

  2. 2

    Remove the top 4 to 6 inches of the soil from the bed of the pond. Fill any holes with a mixture of 5 parts soil to one part bentonite. Grade and role the soil to smooth the pond bed.

  3. 3

    Cover the entire area of the pond evenly with an appropriate amount of bentonite based on the soil make-up and the square footage of the pond.

  4. 4

    Replace a 4 to 6-inch layer of excavated soil over the newly laid bentonite. Avoid disturbing the bentonite layer. Add a layer of gravel to protect the bentonite layer if the pond will serve as a water source for livestock.

  5. 5

    Compact the gravel, soil, and bentonite by tamping or rolling. Refill the pond carefully to avoid eroding the soil and underlying bentonite layer.

  6. 6

    Observe the pond level for the next few days as the bentonite absorbs water and forms an impermeable layer in the pond. Refill the pond if necessary to bring it back up to level.

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