<a href=showthread.php?s=&postid=9212188#post9212188 target=_blank>Originally posted</a> by STEVEBEAM
Hello Mr. Wilson,
First I would like to say that I enjoy reading your posts and respect your experience and knowledge in this field. With that said I have been following this thread and have a few questions.
I have a 210 gallon AGA aquarium and would like to apply shotcrete to the back and partial sides. You said that you applied the shotcrete directly to the glass. Is there any special surface prep that should be done prior to application directly to the glass? Should I leave a separation between the sides bottom and back of the tank for expansion and contraction?
What I am envisioning for my tank is to apply a scratch coat of shotcrete to the back and sides of my tank. Next I will cut dead coral rock with a wet saw and adhere these rocks along with coral rubble to the back and sides of the aquarium. I live in Miami Florida and coral rock is in great abundance. I will of course add plenty of live rock. Your thoughts? Thank You.
There are a number of cement bonding agents designed for wood, glass, steel, and adhering to old concrete. They are basically white glue. It looks like white glue, it smells like white glue, it has the consistency of white glue, and the instructions say that it can be used as....you guessed it...white glue.
The problem with white glue, is it's water soluble. It really aids in adhering the cement to glass, but it dissolves over the next month. Th cement still sticks, but you get stringy plastic-like pieces of glue all over the place. You could use water-proof yellow carpenters glue, but the cement wall is quite stable and will stay in place with gravity alone. Adhering to the wall isn't paramount in most cases.
If you use more cement mix and less aggregate (sand or shell), it will render a sticky mixture. It takes a bit of practice to work the cement into a malleable ball, that is dry enough to stick to the wall, yet wet enough to be workable. Quick setting cement is, as the name would suggest, quick setting. You will find that it will vary in setting time according to how well you mix it, and how much water you add. If you over-mix it, it seems to speed the chemical reaction, and you end up with unusable rocks.
My next project will use egg-crate panels and shelves as a base, and it will be built as a prefab insert (siliconed in place). Working vertically in the tank has its' challenges (gravity, access, and permanence). I will post pictures in the next couple of weeks.
I haven't used a separation point between panels, but it I can't see any negative aspects to doing so.
I would do a dry-stack with the rock. Hold it in place with plastic cable ties, where necessary. Then fill the gaps with cement & shell.
