Someone said the reef welder worked great on their rock. However, reef welder itself isn't tacky, it just forms. So you may want to use super glue with the reef welder to bind the rock to the reef welder.
Just curious, why no epoxy?
I used the 2 little fishes grey and worked good, but jw if you choose not to for aesthetics or another reason
(Note, it did freak out my skimmer for 2 days haha)