I used some bostik 2 part putty stuff. It's pliable etc and then it hits about 3 mins, gets really hot and sets pretty hard. It's difficult to get it to actually "stick" to the surface of the rock though...
agreed.the pratley putty doesnt stick when the rock is moist.maybe a good idea would be to use a hairdryer ony in the area you wanna stick,but at the same time keeping the rock moist once it has been glued.just redid my aquascaping and getting irritated setting the rocks in a way that i have planned and it just keeps falling
I found that as long as you can get the putty around both bits and they dry like that without falling apart - it does not matter if they are actually bound to one another... Quite nice if there is a little give.
I use a 2-part putty too. It does not stick to the rock, but if molded round edges, it tends to set really well and hold the rocks in place.
I have about 250kg of rock in my reef with plenty of caves. I found the best way was to actually drill 16mm holes in the rocks and use 15mm pvc pipe to hold them together, added to this, I used the above putty and 6mm holes with loads of cable ties. The reef is now so strong that I could stand on it without it colapsing.
This is really helpful when adding or removing corals as you can really get some force on them. I will try and load some pics of the build process when I get home.
If you have any old fishing rod blanks, you can use those too, by threading the rod through holes in the rock. You can also quite easily drill through rock to make holes, but be careful not to crack the rock. Using a slightly blunt drill bit usually does the trick. For added stability you can use some Pratley's or Aquamend etc... The blanks are strong and relatively thin so that if you arrange the rocks correctly you can't see the rod.