Pond Boss Forums POND CONSTRUCTION Soil questions Bentonite Questions

I am renovating an old pond. I have got it cleaned and dried out. I have heard good things about bentonite, but dont know anything about it. Where can I buy it, how much should I use, how do I apply it, will it stay on a steep slope (2:1)??? Pond size is 1/4 acre, 14' deep, soil type is silty/small rock upper portion and the bottom is more of a bed rock/decomposed granite.

Kelly B,

I'll try to answer at least some of your questions. I've done some research on bentonite and have had interviews with the owner of the company that mines bentonite in Texas. I haven't used it personally and have found other more preferable solutions than bentonite affords.

In Texas you can buy it in 50 pound sacks at certain feed stores that act as dealers of the product...not sure about your area. How much to use? I've seen many different answers to that question, but suffice it to say that its a bunch. It works best in clay soils spread and mixed in the top layer. I was told you need an approximate minimum 8 inch layer of bentonite to be effective in clay soils, more in porous soils. That's a lot of material.

Also, your chances of success with bentonite are much higher if it is applied to the pond bottom and mixed in the top layer of soil as you have the opportunity to do...as opposed to spreading it on the water surface and letting it sink to the bottom.

You describe a small rock, rocky soil composition. I would be very skeptical that bentonite would give you leak proof protection in such a soil. A liner may be required, assuming that good clay materials are not available. I would sure hate to spend the time and money on bentonite, fill the pond, stock the fish, and discover the pond leaks. Its a gamble and I'd want better odds...that's my 2 cents worth.