Tips on using fijicrete underwater

[jason604]

Hi I'm having some difficulties trying to fijicrete rockwork that's already in my tank. I mixed a generous amount of fijicrete n apply it to my rock that's outside of the tank first. Then as soon as I try to attach it to my rocks inside the tank it dissolves instantly in my tank water. Tried attaching 2 pieces of small rock outside tank n it's also rly hard n keeps falling apart. Any tips? I use very lil water while mixing the Crete to give it a thick consistantcy