Well if I am jaming the plug into a crevis and only need the waterweld to hold it in place, then I dont use glue... Stays soft for a while but gets hard as a rock. I had to remove a frag that only had a nub on the bottom of the plug and it took alot to break it free.
If I am gluing a flat disk, then I just put it in place with the glue then smush a little water weld around the sides to make it look like part of the rock. Sometimes I even jam some aragonite into it so it looks more like rock..
Some times I need to do it in stages as the weith of the frag will make the epoxy sag... after it hardens I can hit it again with some more...