So we’ve proved you can use clumping cat litter to seal a pond because clumping cat litter is made of bentonite clay.
Now, how do you actually do it?
In my first post on this, many people pointed out that actual sodium bentonite clay was available at farm supply type stores. I struck out finding pure sodium bentonite locally, but before you run to Costco and buy $150 worth of kitty litter, go look around and see if plain ol’ sodium bentonite is source-able in your area.
Whether you use pure sodium bentonite or clumping cat litter, know this: once this stuff gets wet, it is gooey. Gooey like the slickest, wettest, slimiest pond edge you’ve ever slipped on. The more water the bentonite clay absorbs, the more gooey it gets, so here’s a few things you shouldn’t do:
Apply this as a surface coating. The clay must be mixed into soil or you’re going to get a pretty nasty layer of clay goop. I know this from experience. Learn from me.
Apply this anywhere you might be walking. The sodium bentonite liner stays soft, like, forever. As long as it’s in contact with water, it has a slickness. See above for comparison to nasty slippery pond edge. You want to fall and break your neck one day? Make a clumping cat litter pathway.
(Related fun fact: you can wet and dry pure sodium bentonite as many times as you want and so long as it doesn’t get contaminated, it’s absorptive properties never go away.)
Ok, now that I’ve firmly emphasized what not to do with clumping cat litter, here’s how you use it to line your pond:
Step 1: Determine how much bentonite or clumping cat litter you need to add to your native soil to create a good seal. There is no exact answer to this because your native soil probably contains some clay already. If your soil is mostly clay or silt already, you will need about 2 pounds of clumping cat litter or sodium bentonite per square foot of pond area. If your native soil is very sandy or mostly gravel, you may need twice this amount.
So you’ll need to do a test.
Sturgis Materials, who markets bentonite clay for pond sealing, describes how to do this. The process is exactly the same with the clumping cat litter:
In the bottom of a 5-gallon plastic pail, drill 20 to 25 eighth inch holes. Gather enough soil from the area to be sealed to fill about 3 inches of the pail. You can either select the most porous soil, (sand) or a mixture of soil taken from several areas of concern in order to present an “average” soil.
In this soil, mix one to two pounds of bentonite and tamp down in the bottom of the pail. Into this pour a gallon or two of water and see if the bentonite provides the necessary seal. If not, repeat the process and increase the amount of bentonite by half a pound until the water is contained within the pail.
The bottom of the pail represents about one square foot. When you know how many pounds of bentonite it takes to seal the pail, then we know how many pounds per square foot to distribute and roto-till into the pond, dam or other earthen structure.
In doing follow-up research for this post, I see that Sturgis Materials is now selling single, 50-pound bags of Sodium Bentonite (from Halliburton, no less!) for $70 including shipping. Like I said, check locally, but in a pinch you could always tell people you contracted with Halliburton to build your pond.
Once you know how much clumping kitty litter or granular sodium bentonite to buy, you have to prepare your pond surface.
Make sure to dig your pond 4-6 inches deeper than the final depth you’re shooting for. After you’ve dug your pond, tamp down the surface very well. If your pond is small, like ours, you might be able to get away with just stomping around in the dry pond for awhile. That’s what we did.
While you are finalizing the shape of your pond, consider the nature of this liner and adjust accordingly. Some of the side walls on our pond were pretty steep. This was a mistake, and it make it far harder to get the cat litter to stay evenly on those sections. Build your pond with gently sloping walls.
When your pond is fine-tuned and tamped down, backfill enough soil plus the required amount of granular sodium bentonite or clumping cat litter to add a 4 inch layer of bentonite-spiked soil to your pond.
Make sure the cat litter is evenly mixed in the soil. We found that backfilling the dirt and bentonite in fairly shallow, 1-inch layers and then mixing each layer together with a grading rake was the easiest way to do this. Obviously, don’t backfill with any large rocks, roots, woody matter or anything that will rot. Now tamp again. Really pack that kitty-litter-soil layer down.
Moment of truth. Time to start filling your pond. Do this very gently so the water pressure doesn’t wear a divot or thin layer in the pond side walls. We used a sprayer attachment to gently wet the sidewalls before beginning the filling process. I don’t think this is necessary, but it’s cool to see the kitty litter swell as it gets wet.
Fill the pond and let it sit for a day or several. Watch for leaks and see if there are any areas where your pond is behaving strangely.
Once you are really, 100% sure this is gonna work, you can add a 2-inch deep layer of protective sand or pea gravel to your pond. This isn’t totally necessary, but it’s a nice additional layer of protection for the bentonite clay and will help keep your pond cleaner.
We ran through about 6 drain-fill cycles on the pond because we wanted extra assurance that the pH and the sodium content of the kitty litter was close enough to neutral to be fine for our ducks and goldfish. I don’t know that this was essential either, but it helped flush the clay fines out of the water too.
That’s pretty much it. The pond’s still holding water like a champ, and the ducks still love it. The male really loves it – did you know ducks prefer to mate in water? Yeah, our drake “prefers” every morning as soon as he and the ladies hit the water.
So what are you waiting for? Build a pond. Duck sex is hilarious.148
Mike @ Gentleman Homestead says
Still no problem with muckiness or nastiness?
This is Awesome! So tempted to do this.
I’m still working with a few large tubs for our growing Muscovies, but now that I’ve plumbed in a 275 gallon rain catchment system near them (upgrade from my 55 gallon barrels), my plan is to elevate a large(ish) prefab pond, drill a hose connector in the bottom of it, so I can use gravity to empty it and fertilize/irrigate my nearby Zone 1 garden area with mucky ducky water…. then replenish and refill the pond with clean rain catchment.
So our initial plan was to go for a duck-a-ponics system and use elevated tables of vegetables and/or duck weed to filter the nutrients out of the pond. We thought we would pump the pond water up and over the plant table as a way of cleaning the water. For a number of reasons (cost, sun, space) this didn’t end up being practical. But in order to keep the muckiness to a minimum we do have some pretty massive filtration at work and we still end up periodically pumping or syphoning the water to the food forest and refilling. I think your plan sounds really solid. The plants love the duck water.
Mike @ Gentleman Homestead says
Very cool. Can’t wait to hear how the filter works out for you over the long haul. Thanks for all the insights.
I did sort of the same thing, using an elevated plastic pond form- but couldn’t get the ducks to use the ramp! I gave up and have it sitting on the ground, and my good intentions of using the drain water for my plants in kapootz. I do use rain water, from a system attached to my coop.
Could you elevate part of the pond? Like put it on just enough of a slant that it would drain with a hose attached (to the side) at the bottom? Or elevate the pond, but mostly burry the elevation-stuff in earthworks of some kind (very likely too much work, I’m aware). Maybe?
I like this idea far better than the plastic liner for ponds. This would work for most pond installations, right? Jack Spirko says having ducks is a sure way to seal a pond from leaks. Sounds like a no fail combination. I look forward to all those light bulb moments. Keep them coming.
Have you tried planting any plants directly into the pond? Or do you keep any plants separated from the pond by planting them in containers above the pond bottom?
In addition to mixing the sodium bentonite to seal the pond bottom and sides, have you tried using the sodium bentonite in the vacinity around the pond to make a sort of marsh / wetlands area around the pond to support plants that liked saturated soils?
Am I right that your pond is drained via the use of an electric pump? (Can’t see how else that would happen.) For the rainy season, where does your overflow go?
All this talk about slippery sodium bentonite has me thinking that it’s probably not a good idea to use clumping kitty litter to get some traction when you’re stuck on a snowy day.
No, for that purpose you want non-clumping clay.
Nancy Sutton says
Regarding obtaining sodium bentonite locally, I did call a feed store, Del’s in Auburn, and their answer to ‘do you sell sodium bentonite’ was ‘No’. (Btw, I’m in Federal Way.)
Further inquiry revealed that they do sell ‘non-clumping cat litter’ (i.e., calcium bentonite), their most popular form, AND ‘clumping cat litter’, at 40 lbs for approx. $9. It’s ingredients are ‘natural clay’… no additives, such as scents, baking soda, et. So… apparently it’s all in the name 🙂
I am a potter, and know that ceramic supply outlets carry Bentonite in large quantities. I just checked Clay Art Centre in Tacoma and they have several kinds. It appears one of the cheaper ones is $29 for 100 pounds. Maybe this would be a good source for a pond liner.
Well drillers use sodium bentonite in 50# bags for the surface seal on drilled wells. One Washington wholesaler is RGB in Kirkland. See- http://www.rjbwholesale.com/catalog/rootCat/id/16
Dennis Carlson says
I agree with Jack Spirko that ducks prefer to poop in water. What works best for me is a heavy duty plastic stock tank that I can barely lift by the edge to dump out the water. I then rinse it out, move it to another spot, and fill it every day. My 12 Anconas quickly learned to use a long gentle ramp to get into the tank. They are surrounded by mobile electric poultry netting in the orchard during the heat of summer and then out to an open pasture during the winter. They love cold rain and have refused shelter even in the worst winter blowing blizzard conditions here in Hood River, Oregon. The really cool thing about these ducks is that they reproduce on their own without a noisy rooster. They lay lots of eggs and are good to eat.
I also got my Anconas from Evan and Rachel at Boondockers Farm and enjoyed your Podcast with them.
Very informative and useful information has been shared by you about pond fine-tuned and tamped down plus the required amount of granular sodium bentonite , Bigger is not necessarily better when it comes to the size of the ponds .Several small- to medium-sized ponds are easier to maintain. To have problem free pond need Pond Pro 2000, so that you
Great articles thanks. Can you please do an article about your pond filtration methods to clean the water and how you use that water.
Seattle Pottery Supply sells Bentonite at about $22 for 100 pounds. You might want to check with them before making a trip to make sure it is the correct type.
Bentonite as a potter’s ingredient is supplied as a super-fine powder rather than granules. I doubt it would perform the same way as kitty litter.
So… How’s that duck pond working out for you??? We’re looking at potentially putting one in this summer, and wondered if this would be a good option. I’d love an update post and/or a post about your filtration process if you have time!! 🙂
This is great. I have been looking for a pond option for my future ducks and am considering anconas as well! I was at the Mother Earth fair too. Wonder when you will be speaking there yourself! You’d be great.
Just wanted to reiterate the request for info on your filter system and/or using duck pond water for irrigation. :). Keep up the awesome duck posts!
Great tutorial. Does the sodium leach into the water?
Joe Sangemino says
Great article, although I’ve been lucky and have soil with a naturally high clay content, so that, and a little ‘duck poop’ seems to seal pretty well.
Yes, Duck Sex is hilarious. What is even more of a laugh is when our new rooster decides to get amorous with our female duck. The frantic quacking can be heard from quite a distance, and then for some unknown reason, our older rooster always intervenes and defends the duck by chasing the misguided rooster off.
More fun than cable TV!
Well drillers use bentonite.
50 lb for $15 last time.
Check your Yellow Pages.