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Discussion Starter · #1 ·
Hi...

I'm finally on the verge of setting up a 125 gallon mbuna tank. There's so many wonderful tanks on this site, especially with the custom backgrounds. But, I wanted to try something different. The background entirely consisting of rocks looks a bit unnatural to me.

A number of Lake Malawi photos show some big honkin' boulders, surrounded by smaller rocks. I can't fit a 5 ft. diameter rock in my tank, so I opted to try and create a look where the tank creates an imaginary cutout of those boulders.

I used styrofoam and quikrete mason mix to create two "sections" of boulders. One will fit on the lefthand side of the tank, the other I'll stick against the back somewhere. (I plan on painting the background black). Once I throw in some natural rocks, I'm hoping they blend in well.

Here's the rocks I'm using:
http://s284.photobucket.com/albums/ll28 ... lrocks.jpg

And here's the custom boulder cutouts:
http://s284.photobucket.com/albums/ll28 ... round1.jpg

http://s284.photobucket.com/albums/ll28 ... round2.jpg

I'm certainly open to feedback. This was my first effort with cement. A couple of things I discovered:

1. The quikrete mason mix produced a nice texture. Adding sand created texture that was too rough.
2. A little color additive goes a long way!
3. I made sure one rock was slightly different color than the other.
4. Spritzing with water and colorant was very effective. Just a couple drops in a water bottle!!!
5. Using a ripsaw was surprisingly effective for shaping styrofoam.

Let me know what you think! I'll post pics of the tank when I'm done. Hey, if it looks awful, I'll just go with rocks!
 

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Discussion Starter · #2 ·
OK, I finally figured out how to post the actual pics. Sorry for the links earlier:



 

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I dont understand what you're doing, really...A 5 ft boulder in the middle of the tank look? why? I dont really get why you'd want to create this illusion. I'll stay tuned though.
 

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Because this is how it looks in the lake. Many people try to create tanks that appear as though they're a section from the lake. If it wasn't so cost-intensive, I'd get a 3 foot rock and have sections cut out of it to put into the corners of my tank.
 

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Discussion Starter · #6 ·
Laurel's got it exactly... the pics I've seen of the lake have some pretty big rocks scattered about. I like the idea of people making a custom background out of cement and styrofoam, but I thought the disadvantages are that they take up too much space, and ultimately look unnatural.

I have no idea how this will look when I set it up, but if it looks terrible, I'll just toss out the fake rocks!

RE: ripsaw, my terminology might be off, but just a basic saw used to cut wood. Nothing fancy. I started with a hacksaw, then a smaller utility blade, and found the best approach was working with a good ol' handheld saw.

The rocks have dried, but I learned that without cement on the back, the edges started to chip off when I started soaking and curing them. I went ahead and hollowed out the rocks, added cement on the backsides as well, so in a day I'm back to curing for two weeks.

I'll post some pics when I get a chance...
 

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Discussion Starter · #7 ·
Update:

What a total bust!!! I'm hugely disappointed. I hollowed out the backsides, added more cement, and the dang things still float.

****.

I think I might try this whole process again, except sand cast the rocks instaed of shape them around styrofoam. Any thoughts?

What's the best way to shape a section of a fake boulder without relying on super lightweight material?

Back to the drawing board...
 

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Discussion Starter · #8 ·
OK, fueled by frustration and the glimmer of hope that I've got a better idea, I went back to the drawing board.

For the record, here was the old result:



I bought a custom stand that needed assembled, and I realized that it's original crate packaging provided a pseudo-mold. I placed wax paper in the bottom, mixed up some cement, and then just basically shaped the rock that I wanted out of relatively non-soupy cement.

I played around with using other rocks for forming indentations, and then just basically used my hands to mimic the shape of other rocks and create some crevices (using gloves, of course!).

I'll still spray it with some colorant in some spots, but here's the result.





Two thoughts I had... I screwed a plywood board into the back of the crate frame, just to make sure it was totally flat. I'm trying to make sure the rock sits right up against the glass. Also, the other thought I had was to make sure I bevel the back edge, in order to leave room for the tank's seal in the corner.

Any thoughts on how to do this better? We'll see how easy it is to peel the hardened cement from the wood and the wax paper.
 

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I've used concrete and styrofoam before, the trick is to make the rock in styrofoam, give it several coats of concrete on the front, then cut and melt away the styrofoam with a heat gun and give it several coats on the back.
 

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Not that I know how to do any of this coz I am actually following your thread for inspiration .... but .... say you use your original idea of utilizing the styrofoam, except make the rock 'inside out'.

See what you think of this ... by all means pick it apart too :D

  • Use styrofoam pieces stacked and glued/siliconed together; maybe four to six 4' x 8' @ 2" thick which are then cut in half or quartered before bonding.
    Then carve out the rock mold.
    Remove the loose gunk with a shop vac.
    Then gently heat the styrofoam with a heatgun/hairdryer to get it smooth so you get that boulder smoothness (or leave it rough).
    Line it with wax paper or cling film (saran wrap) before pouring in your mixture.
    Once your mold is filled, level/flatten the back of your mixture (using something like a bricklayer's trowel).
    Attach something flat yet solid (some plywood) to the back of the mold.
    After it is hard enough to be moved and keep it's shape but not fully hardened, carefully flip it upside down and remove the mold.
    Now you can spray the extra coloring you wanted and then let it cure.
    Result will be your original idea but with it's own weight.

Hope you get to see what I'm getting at - maybe you can even improve on it. 8)

Regards,
D
 

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Discussion Starter · #11 ·
Hey D-007, I like your idea... my only thoughts would be that you don't have much control over the texture and surface of the visible surface of your rock.

I just checked out my first "rock in a corner" this morning. So far, so good! the two corner edges are perfectly smooth... I pulled them away from the sides of the wooden frame. After 7 hours, it's dry enough to hold its shape, but I was still able to carve away a bevel to leave room for the tank's seal.

With my previous messup, I know now how much styrofoam you need to remove! Lessons learned...

I think I'm going to make one more rock for flat up against the background, but I've got some styrofoam left. Unlike previous effort, I think it's much more cement, and less styrofoam!

The only disadvantage I can see to leaving out the styrofoam altogether is that the result weighs more (minor concern) and you use up much much more cement. It ain't expensive, but it sure is heavy lugging it from the store!

I'll try and post pics later, especially after I work on the 2nd rock.
 

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Discussion Starter · #12 ·
OK, so more progress. Now that I've got this process rolling, I'm having some fun with it. I made two more rocks shown here:





I was modeling the narrow rock after some of the flat rocks I've got in my pile of natural rocks. Let me tell ya, that was hard to create... even though I mixed the cement pretty thick, the first result looked... um... slightly "suggestive". I think my wife wondered what the heck I was doing!

I waited for that to harden and then added yet another layer of cement to try to create more angular surfaces.

Here's the first rock curing in a tub of water.



I've basically got everything curing now and should be setting up the tank in about 2 or 3 weeks.
 

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gherlevi said:
I was modeling the narrow rock after some of the flat rocks I've got in my pile of natural rocks. Let me tell ya, that was hard to create... even though I mixed the cement pretty thick, the first result looked... um... slightly "suggestive". I think my wife wondered what the heck I was doing!
Should have kept it; I'm sure you'd have got some lively comments on it :lol:
 

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Discussion Starter · #15 ·
Hey D-007!

Basically, it's been a waiting period of curing the rocks. After about two weeks, these things are still bumping up the pH, but it's getting better. I just picked up the tank yesterday, and I finished the stand. I'm changing water for the curing process every other day.

Estimated assembly is in approx. 1 to 2 weeks. I was going to take pics of the DIY rocks in the tank, so I'll make sure I post those.

I'm pretty excited to see how well they match the actual rocks that I picked up. But, when algae starts to grow, that should offer a nice "nature's fudge factor".
 

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Discussion Starter · #17 ·
Well, the tank is finally set up!

Here's some pics. Hopefully, the three DIY rock are subtle in the final setup. All three are very flush against the glass. The only odd thing is that you can see a gap between the rock and its reflection due to the clear glass!

The background itself is painted flat black.

Here's the DIY rocks:



Here's the DIY rocks with natural rocks added:



...and here's the full setup with sand and water. Forgive the oddball reflections and "new tank" bubbles on the glass:

 

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Discussion Starter · #19 ·
Thanks quiksilver...

Yeah, I was snapping photos quickly while setting up. In a day or so, I hope to take better pictures at night.

What, you don't like the lampshade that I stuck in the middle? :)
 
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