How much clay to gley a pond in sandy soil?

My climate is really hot and the soil is all sand. I thought if I have a pond I could grow bananas and papaya around it to provide some shady micro-climate for aquaculture. So the question is, how thick of clay do I need to lay to seal up the pond? I could layer it with green plant material to gley it, but I know in the long run I will still need to have substantial clay. But how much?

This is only my experience of using clay to line a pond in very sandy soil, other people may have much better ideas.

In drawing A, the almost pure clay (grey) was laid thick all over the pond bottom and sides and came right up to the edges where it was smoothed by hand to create an impermeable barrier.

Water needs to be in contact with the clay at all times, if it dries out it will crack - even with the addition of lots of animal waste and organic material - and the water will run through to the sand, taking some clay with it, lowering the level and speeding up the loss of water due to cracking. See B



The loss of water and clay led to a situation where there was some clay at the bottom of the pond (As in C) but the level of the water not as high as I would have liked. This stayed stable for a few years which indicated to me that it's possible to clay puddle a shallow pond which is regularly filled with water but if the edges are too straight, in time, the clay will be lost through cracking and move downwards.

It's difficult to say how much clay you'll need without knowing more about the purity if the clay, the size and depth of the pond and what your arrangements are for filling it. Do some experimenting in a small hole and work with the clay for a few weeks to see for yourself.

We've now used concrete to line our pond in sand but if anyone has succeeded in making this work, I'd love to know how you did it and I'm sure Nathanael would too.

Thanks for sharing your experience Irene! If your drawing is an indication, it looks like the sides of the pond were significantly steeper than a 1:2 ratio. Might that have contributed to the clay displacement?
(Checked out your site--awesome work!)

So I did the internet calculation on how much bentonite I needed, added a bit more than that and I have pretty good clay soil. I should have done more. Do way more than people say imo.