Natural Pond Liners
Clay pond liners have been used for centuries to prevent water from seeping through pond soil. The best clay for creating pond lining systems is sodium bentonite clay. Sodium bentonite is a pond clay that originated as very fine volcanic ash. The clay swells when it comes in contact with water. This swelling characteristic forces the pond clay into soil pores sealing the pond bottom. For best results, the clay should be compacted into dry soil using a vibratory roller.
Other pond sealants such as long-chain polymer sealers can be used to supplement bentonite clay. The polymer pond sealers can also be used to repair leaking ponds. Soilfloc, a 2-part polymer, can be applied through the water to stop pond leaks without draining the pond. The polymer sealers are often used to fix leaking dams when it would be very expensive to drain and seal the dam with clay.