Only using 15% epoxy would make it more affordable and I guess the added advantage of using epoxy is there is no shrinkage.
There is shrinkage with epoxy. But not that much, that it will do harm, if you don´t use to much epoxy.
15% is a common value, because it is just enough to glue all the stone-surfaces together, but not that much to leave a lot of space just filled with pure resin.
The resin will shrink, the stones (or metal-chips or whatelse you will add) not. Less epoxy means less shrinkage.
You just want to build a stiff grain skeleton.
Therefore you have to chose different sizes of chips, stones, sand. Each smaller size fills the gaps, the bigger sized parts have inbetween.
Have you tried bentonite clay in the mix?
No, I haven´t. You mean clay in a powder-like consistency ?
Adding powder-like substances usually has no advantages.
It adds no structural strength, but you need a lot more epoxy to cover all those uncountable little surfaces. If the surfaces of the powder is not covered with epoxy, you get weak points, which means cracks along the grain boundaries.
It´s quite the same as with high-strength concrete.
This is why I use quartz-sand 1-3mm, it has nearly no particles under 1mm. Common sand has much to much powder-like parts.
