building foam wall

i am thinking of making a foam rock wall as a backdrop to my aquarium, i have no idea where to even start so lots of help would be great. just for my 40 gallon reef tank i have. i want to experiment on the 40 before i try the 90

 

Spray foam, block foam, full sheet just carved?
I built a few for freshwater.

 

do i need to use egg crate? i was researching and it said attach some rocks to some eggcrate cut to fit in your tank then spray foam between the rocks, would this be the right way? also how do i make it not flat i want like some spots where i can put coral and such. or like an archway.

 

Basile built an entire underwater structure out of foam and dry rock.

http://www.3reef.com/forums/show-off-your-fish-tanks/biocube-65-g-underwater-sculptures-76259.html

 

Another guy on here built it the way with egg crate. I don't remember the name. sorry. Yeah that's one way of doing. It looks nice and pretty natural once covered in algea.

I, however, don't use eggcrate. I have done it a few different way. I have cut it up in blocks, carve, and silicone them to together to create a rock wall. I just silicone a few uncarved blocks to the glass to get a base to build off of. Then it's the fun part. Cement everything. After everything is in place and dry. Fill the tank up a few times (I did 20x for my 20 gallon tank) to get all the nasties out of the water. The cement then shouldn't do anything to the water. My last fill I let sit for 2 days then drain it completely fill up n start putting stuff in.

I can show you pictures of my 20 gallon if you want. It's done a different way, just a single sheet cut to the tank size and carved.

 

a pic would be apreciated, also is there a way of doing this without emptying the tank or at least not all the way?

 

also do i have to worry about the foam harming the inhabitants do i have to get a reef safe one?

 

You want it empty. It way easier and less harmful to the tiny creatures you may have. For the stray foam I do not know the right stuff to use. I only use giant sheets of Styrofoam you get from lowes. uploading pictures now.

 

thanks for the info, i am not sure wchich method to use, how do you make the Styrofoam look natural? also do i just cut the foam to fit around the overflow?

 

sorry about the dirtiness, tank cleaning day.
Here are a few pics.





Just carve it. ha sorry its hard to explain. I use the 2 inch stryofoam, so I can carve into a ton.