lol- dendroboard vet here-
This seems to be more complicated than the gs/coco backgrounds.
Another method we used is the flevapol method, which is a concrete binder mixed with water and coco fiber(sand in this case) to make the background. Its 4 parts solid mixture to one part binder. The only binder recommended is the Ace concrete brand and the Quickrete brand. It takes awhile to dry, almost 3 days... fans speed it up. The plus to this method is that it is ALOT less time consumiing, and less messy. Oh yeah, and cheaper
This would eliminate the use of epoxy. The only problem I see is possible PH raises until it cures, but until then...
Just some thoughts