I use Home Depot's Aquamend along with super glue gel from the Dollar General (2 tubes - $1.00). Aquamend takes awhile to cure. I'll take a frag, dry the bottom, apply some super glue gel, then apply a small glob of Aquamend, apply some super glue gel to the Aquamend, and then apply to rock. Hold it in place for about 30 seconds without moving. Do not try to move or re-position. If you do, start all over. I've found the super glue gel bonds more quickly, allowing the Aquamend a chance to cure, which does take awhile. On rare occasions it does not work, so I'll reapply. Have never had to do more than one "do over." Frag will encrust over this application. Believe some other Members mount frags in a similar manner.
Good luck !!!!