While looking for clay to seal my leaking pond I ran across Old Hickory Clay Co. http://www.oldhickoryclay.com They are in Tn only about 100 miles from me. They mine clay to use in pottery. They call it Ball Clay. I gave them a call today and they said that their clay is used alot to seal ponds. My soil is about 25% clay and I was thinking that adding some of their clay and mixing well with a tiller may do the trick for a good seal. So is clay just plain clay no matter what or are some better than others? I know bentonite is the best but shipping is way too expensive. I just wanted to get the experts thoughts before I did anything. Thanks