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Discussion Starter · #1 ·
...That I will not be building for my new 55 setup because it is winter, and New England is very chilly this winter. However, I will share this method with you all in case you are somewhere warmer where this procedure will work right now.

So, I am a geologist, more specifically a paleontologist. We are constantly casting rock surfaces so we can take the peels back to the lab to compare/study/photograph. So I know a bit about rocks, and how to take a really big rock and get an accurate representation of its surface right down to individual sand and clay-sized particles. Conceivably, this procedure could be used to make seamless ultra-realistic backgrounds for any size tank.

The Materials

Release agent (in a spray can) - can probably find at a Home dumpster type store or online.
Liquid latex, something like Cementex latex #80. Can find this online for about $40 a gallon.
Great Stuff-like expanding foam insulation. Aubuchon's has a better, harder version.
Sytrofoam insulation board.
Fiberglass resin and glass mesh
Disposable 3" paintbrush
Level
Measuring tape
Pencil/chalk line
Broom

The Process

1) Go out cliff hunting. By cliff, I do not mean a thousand foot high precipice, simply a rock wall that sticks up out of the ground. You could find something relatively flat, or something with as much relief as you would like - it doesn't really matter. Once you find your outcrop, measure your tank dimensions onto the selected area of the cliff face. Mark out your dimensions on the cliff using your chalk line or pencil or a piece of white chalk. Do not use permanent marker or paint.

2) Clean the cliff off a bit. Get the larger debris out of the cracks, off surfaces, etc. Doesn't have to be perfect.

3) Apply a light coat of the release agent onto your selected area (this step is not really necessary, and I don't know how safe the release agent may be for your fish, but the resulting mould can be washed using dish soap later...).

4) Start latexing. The first coat should be thin and even. Dab the latex into all of the crevices. Try to avoid as many air bubbles as possible. Work from one side of your area to the other, trying to avoid going back into your painted areas once you have finished with them. Let this coat dry thoroughly.

Apply the next coat thicker, but not overly so. It should be thick enough that you cannot see any of the underlying layer, but not so thick that drying time will be 2 days. If your cliff is in direct sunlight and it is warm, the latex will set up quite rapidly - as little as an hour. You may have to wait a day or 2 for this coat to dry.

Apply the third and final coat. This one should be really glopped on. You want a nice, even, thick coat of latex to cover the entire surface. Let this dry thoroughly.

5) Removal. This is kind of fun. Starting in a corner, use the tips of your fingers to roll back one of the edges of the latex. Once you have it started, gently pull the latex off toward you, a little bit at a time. Take your time, and use your fingers. You don't want to have your hands far from the point where the latex is peeling off from the rock, keep them close to the rock, otherwise your mould could get stretched out of shape. Once you have your mould completely peeled off the rock, stand back and look at the perfectly clean rock in front of you. The latex peels every little bit of dirt off of the rock. Take a picture or 2 of your cliff - this will be good reference material when you paint it.

6) At home in your workshop/basement/garage, cut a piece of foam insulation board to the exact dimensions of the inside glass of your tank. Get out the great stuff. So, what you will want to do now is to recreate the topography of the original cliff. Your latex is flat, you want to make it 3D and sturdy. What you will end up with in this part of the process is a negative of your cliff. Lay out the latex over the board, and trim it to slightly larger than the foam board. Decide where the high spots are, and begin to fill in the space between the foam panel and the latex with great stuff. Keep this process up gradually, allowing an hour or so between layers of great stuff for it to partially set. At teh end of this phase, you will have a perfect replica of your cliff, only inside-out.

7) Apply a thin coat of release agent into your new cliff mould and allow to dry. Now, there are a few options here for the material of the finished outside edge of your cliff replica. I think an epoxy resin would work well, and should be completely inert. Another option would be fiberglass resin, with glass fiber mesh in the second coat, not the first. You want to pick up all the detail from the original mould first. Then use glass fiber mesh in the second coat, then another coat of resin.

8) After the resin has completely cured, begin to form a thick (2-3") layer of greatstuff over the entire back of your cast. This should extend slightly past the edges of your insulation panel, as you will later trim this off flat and silicone it into your tank. Allow to cure. Apply another coat in the areas of high relief.

9) Separate the cast an mould. It may be easiest to disassemble the could portion until you can get the latex, and then peel the latex off of the resin. Wash thoroughly to get rid of any trace of the release agent using dish soap.

10) Trim the background to its finished dimensions - take your time and measure twice. A table saw might work well, or a sawsall with a fine blade, or a band saw or a hand held jigsaw. Paint the entire background. I am not sure what fish-safe paints are available, but someone here must know - I think drylock is safe, and it has a sandy texture that would work well.

Were it not winter here I would have nice pictures to go along with this, as well as a few additional pointers from having done it. I have had this process in my head for some time now, and just thought I would share it with you all so you could try it if you want. I had a really nice columnar-jointed basalt outcrop in mind as well - it would have been great, but because of the weather, I ended up having to order something online for $138 bucks. Oh well. If anyone does try this technique, please post some photos.
 

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That sounds a heck of a lot easier than what I'm doing.
http://www.cichlid-forum.com/phpBB/view ... &&start=15

I've seen a lot of rock structures for pools done that way around here. Too bad about the weather in your area. It would have made a very interesting post.

Thanks for sharing the technique. :thumb:
 

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Sand can make a very detailed and high relief mold too. You mix uncooked oatmeal and molasses into the dry sand to give it a dough like consistency. Then you can make an impression in it with one or more rocks, driftwood, etc. You can press different sides of the same rock in different places to create a rock wall without the repetition, mortar joints or seams you often see in the styrofoam backgrounds.
 

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trigger said:
I've seen someone doing something like this, but he was covering the rock with fiberglass and got an instant hard copy of the rock formation he could place in his tank. I've lost the link and can not find it aymore. The rock was on some beach, you could see the sea behind it.
Sounds familiar, I think I remember seeing that beach too. Seems to me it a company site. They were selling polyurethane rubber in a cold set paintable form, so if we saw the same place, there was one more step.
 

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trigger said:
The site was a large page covered with a lot of explaining text... Can't remember if it was a company indeed, but could as well have been. You don't happen to remember the link do you ??
Yes, that matches my memories. I tried a few searches but couldn't find it. Something makes me think it might have been British. I should try a search again. I think they spell it "mould".
 

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Here's one version of the same procedure. This is originally from a Finnish forumbut has recently been translated also in english. Hope you find it useful.
 

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Discussion Starter · #9 ·
Nice link, thanks. Essentially the same procedure, just different agents used, and done on a smaller scale. I think I'm going to try this with a smaller tank this spring, maybe just a 10 or 29 to get the process down.
 

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i did the same thing with my fiberglass background for the old 700g i had in NY

I just piled up some rocks and sprayed them with wax and using a very rough weave fiberglass cloth i just painted on the epoxy. because you do not need 100% water tight epoxy for just the background you can use the much cheaper bondo brands. after i got a few pieces done i glued them up on the back of the tank and then painted them with colored sand that i mixed with the epoxy.

I have been thinking about doing a new background for the 220g i have.
 

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jcollette3 said:
Were it not winter here I would have nice pictures to go along with this, as well as a few additional pointers from having done it.
Well it is no longer the winter, but instead midway through the summer. bumping this in the hopes that perhaps you've gone through with your project and have some pictures and additional pointers to share.

the directions are great, but being far from handy the more details and pictures the better!
 
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