I am planning to build a bunch of miniature rock walls in my next project and I need something that looks vaguely like mortar to glue them together with. Yes...this will take a while. I've looked at grey epoxy, which SHOULD ( but may not be) inert after a weeks curing. I've also looked at grey silicone but I cannot find any information on what is or, more importantly, is not in those produces. Anybody know anything? Don't want to go to all that work and kill the little fishies and plants.