Pond Boss Forums INTRO Questions & Observations 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 some of your questions. First, I should say I have never applied bentonite to my ponds. I have had problems that included bentonite as possible options for solutions, necesitating my own research on the product. It is this research from which I will base my responses to your questions. This research included interviews with the owner of the company that mines bentonite in Texas.

Where to purchase? In Texas, it can be purchased in 50 pound sacks at a local feed store that is a dealer for the product. Don't know about your area, but would try feed stores first.

How much to apply? A difficult question. The answer depends on your specific situation, your soil content, the problem you are trying to solve. Bentonite is best applied to clay type soils and has the highest success rate when applied to an empty pond bottom. To give you an example of something which I am very familiar with, clay. You need 2 feet solid of good quality clay to insure that a pond does not leak. How much bentonite? I've been told you need 8 inches minimum, but I question that bentonite is that much better than clay, if at all in holding water. At any rate 8 inches is a lot of material and to be safe, I would go much more, especially over a small rocky bottom surface...a surface which bentonite is not optimum for.

How to apply? You need some equipment to apply that much material. A spreader and a tractor with disk to mix it in the top layer of soil....if you can get a tractor in the pond...if not a dozer may be required. You can try just spreading a few bags of the material by hand over the bottom, but again depending on your situation, that has a low probability of success.

Will it stay? Yes, especially if mixed in the top layer of soil. If applying to sides, I think I would use a small dozer to pack it in good, but again you could also try the hand method.

Bottom line...it all depends on your situation...but from the data you have provided, if you do not have access to good quality clay, if the soil is rocky and not good clay, then I think I would look into a liner rather than bentonite....my 2 cents worth. Good luck.

I am no pond expert, by any means, however, bentonite I know about. Dry, powdered bentonite clay expands at approximately a 15 to one rate. I.E., if you put it down in an even 1/2" layer, and it's undisturbed, it will eventually (in a perfect world) be equivalent to about 6-8" thick. Sounds as though most till it into the top few inches of soil, so it actually is even thicker in the end.

The stuff is amazing. We've used it to seal off underground tank vaults to keep ground water from entering. Pour it down a well and it means a permanent seal that no groundwater or surface runoff will ever penetrate.

Doesn't really take that much, if it's an unbroken layer. Can't remember for sure, but a 50lb sack was along the lines of $8-10...by the ton, it's gotta be cheaper.

Matt,

The 15 to 1 ratio is interesting....when the Texas bentonite folks told me 8 inches of bentonite was required to seal a pond that already has clay in it, I assume they meant 8 inches of the material, not 1/2 inch of material which would expand to close to 8 inches. So, are you saying that 1/2 inch of material is all that is required?

That would indeed be amazing stuff, if in fact that is all that is required to effectively seal a leaking pond.

Just an off the wall remark...

I saw some cat litter that is made out of the stuff (with kitty perfumes of course)!

Did it leak?