Concrete to bond rock?

[Delphinus]

My tank is still using rockwork that was bonded into shapes using the stuff I found.

FWIW I don't even think "Emaco Architectural R400" exists anymore either, it's called something else now (because why not change the name a bunch more times).

I *think* this is it now: http://www.jamacsales.com/dt_portfol...architectural/

I have no idea if it still sets at a neutral pH. I would presume so but would be worthwhile researching or experimenting first before going full on with it in a new tank.