Pond Boss Forums INTRO Questions & Observations Sodium Bentonite

Looking for info from anyone who has used Sodium Bentonite to seal their pond. I have about a 3 acre pond that has little to no clay in it. Also just below the bottom of the pond is silica sand. This is going to be real expensive to do so I was looking for some feedback on this product before I attempt it. Thanks Mike

Mike, I have tried it several times with no luck. Maybe others have had better results.

No luck with bentonite. Several attempts. I used the "find the leak and pour it in" method. The problem is that the stuff is so fine that if the water finds a way around it that it just dissolves it. It is a very dispersive clay and will completely dissolve in water. I tried an experiment where I put some in the bottom of an aquarium then filled it with water. The stuff keeps absorbing water. Then it becomes so dispersed it starts floating up. After week in perfectly still conditions all the solids disappeared and it formed a sort of haze throughout the entire water column. It was denser on the bottom. However not like say pudding. More like heavy cream.

I think you will need lots of fines (very small particles bigger than clay but smaller than sand grains aka. silt) in order for bentonite to work if you use the "soil mixture method". If you have coarse sand I think mixing in bentonite will not work very well. I have never tried that though.

The bentonite did help me in one way. When I first started, the pond was leaking but there were no holes (because the whole bottom was porous but I didn't know it). I sprinkled bentonite over most of the bottom (granular) and it made a light coating which sealed most of the bottom temporarily. Some spots had less and the water leaked faster there. This washed away more bentonite which made it leak faster. Then I had a real leak going and could see it. However plugging it didn't help as it would spring a new leak immediately and very close by. However if I spread a bunch of bentonite there then a new leak would form randomly somewhere else.

This made me realize that the whole bottom was porous.

I finally lined the whole pond with 3 feet of clay. Had a drought and the liner cracked then filled in the middle of winter and thawed the part that was under water. The liner shrank as it thawed and caused leaks. Spring. Used bentonite but it didn't work because it just washed through (I used the large lumpy kind used for fixing leaks). Finally I hit on the idea of just chopping up the same clay I used to line the pond. It had some fines. I then mixed with water to make mud and poured down the leak. That worked. Recently I got another kind of clay with even more fines and it plugs even better. After the leak is clogged I top the hole off with 100% clay so I don't get any seepage.

If you have a bluestone quarry near you they usually make something called "Modified". They crush bluestone into "crusher run" then wash this of all sand and clay to make the "modified". You don't want the modified as that is used for drainage. You don't want the sand either. They usually have a settling pond to keep from polluting the rivers. In that pond will be stone silt mixed with clay. It is great for patching. Just make sure there is enough clay in the mix to keep it from seeping. Might be just the right stuff to mix with bentonite for a patch mix.

I finally got the pond sealed to the point where it only loses on quarter inch a day with no water coming in. Might be evaporation or I might still have a leak I haven't found yet. That is about 3-5 gallon/minute leak. Much better than when I was leaking 200 gallons a minute.