The presence of water transforms the feeling of a garden like few other features in the landscape can. Ponds bring wildlife to the garden and provide the opportunity to grow stunning aquatic plants that would not otherwise be possible. However, a pond that does not hold water well, quickly becomes an eyesore and can make you wish you never set out to build one in the first place. Fortunately, there is an effective, all-natural way to repair a leaking clay bottom pond. Bentonite clay is a form of volcanic ash that makes sealing it a manageable task.
Draining the Pond
The first step to repairing a leaking clay-bottom pond is to dry it out completely. If there is any water remaining, it needs to be completely drained. A submersible pump is the most effective way to go about it. It will drain the water down to an inch or less, but it is necessary to dig a hole at the lowest point so the pump can drain the last bit of water. Pumping out the water an additional 4 to 6 inches below the lowest point in the pond allows it dry enough for bentonite to be applied.
Preparing the Soil
Once the soil is dry, it needs to be tilled up with a rototiller so it can be mixed in an even consistency with the bentonite. Any leaves, sticks or other debris that has accumulated at the bottom of the pond should be removed prior to tilling. For best results, the soil should be tilled to fine consistency to a depth of at least 4 inches over the entire pond area. Tilling has the added advantage of exposing the soil to air, so it can continue to dry before it is mixed with bentonite.
Bentonite is usually applied at a rate between 2 and 4 pounds per square foot. This is the equivalent of 1/4 to 1/2 inch coverage. If the pond has only a slow leak, a 1/4 inch layer should be fine. For a serious leak due to rocky soil, apply a 1/2 inch layer or more of bentonite to be sure that a good seal is made. Spread the clay evenly over the entire surface area and till it in to mix it thoroughly with the native soil.
Compacting the Pond Bottom
After tilling, the soil should be raked into a smooth surface and compacted before it is allowed to get wet. It is critical to do this immediately so that rain doesn’t come along and wet the bentonite prematurely. A hand-held metal tamper can be used for small ponds, though a gas-powered or electric tamper will be much more efficient for large areas. After the entire area has been compacted into a firm surface, the leakage should be resolved and the pond can be refilled.
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