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Discussion Starter · #1 ·
Hi all, I've seen some previous posts here about DIY fake rock backgrounds, using cement etc over polystyrene/styrofoam.

I have a 450L aquarium I plan to set up for malawi cichlids and am in the process of creating a rock background. I'm confident that I can make it look good, but I don't really know as to the long term durability. I've seen people here mention 'drylok' to be used on the outside, but that's not a product I can get here. I

I've done two thin coats of cement so far and just want some tips on how I can insure this stays looking good for years to come.

I'll post a photo of what I've done so far, if that helps.

Any help would be much appreciated!
 

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Order some pond armor to coat it with. It is a clear two part epoxy that will seal it so it stays durable. It's not cheap, about $72 for the smallest kit they make which is 1.5qts, but it is well worth it to make it a long lasting background.
 

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Discussion Starter · #3 ·
Hi, thank you for your reply. Won't epoxy make it look all glossy and ruin the effect? Or can't you tell when it's submerged?
 

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Out of the water it is shiny, but once in the water the gloss is not apparent at all once submerged. I have a number of pictures and videos in the DIY section, if you get a chance check some of those out and you'll see it isn't noticeable at all once the tank is filled.
 

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Also just a little tip for ya in case you do use Pond Armor. When you mix it add about a table spoon or so of denatured alcohol into the mix. Pond armor is extremely thick and the D.A makes working with it a whole lot easier.
 

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Discussion Starter · #6 ·
Seems like a lot of builds here recommend DryLok, but that's not available anywhere I can see in NZ.

Seems like some options are:
1/ Use just cement and tints[/list]
2/ Use epoxy to coat
3/ Rubber sealant that seems like DryLok? Only available in black, but I wonder if some white acrylic paint rto grey it?https://www.liquidrubber.co.nz/product/waterproof-sealant/
4/ Cemix crystal proof https://www.bunnings.co.nz/cemix-2kg-crystalproof_p00142069

It's hard to know what to use when none of the products people use are available locally
 

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I have no experience with this particular type of background, but wanted to chime in as a fellow Kiwi. I feel your pain regarding virtually none of the products used in the US being available in NZ.

What I like about Cemix is that it's approved for potable water. That means you can be 100% sure it will not leach anything harmful to fish into the water. It's interesting that they say the concrete can still 'breeze'. I would carefully monitor the pH after filling the tank. If the concrete still makes the water alkaline, it could take a few weeks to subside.

Best of luck with your project, and please let us know how it turns out. It would be nice to hear about some real life experiences with Kiwi products.
 

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Steve C said:
Also just a little tip for ya in case you do use Pond Armor. When you mix it add about a table spoon or so of denatured alcohol into the mix. Pond armor is extremely thick and the D.A makes working with it a whole lot easier.
I can second this. I forgot to do this and it was really thick. Also, it doesn't go near as far that way. I have since used it thinned and it goes a long way without hurting the outcome.
 

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Discussion Starter · #9 ·
Thank you all for your replies. It's good to see another kiwi around and I'll definitely post some pictures. I think I'll epoxy it as my it'll give it durability and means I can use some watered down acrylic paint to create depth and not worry about losing my detail over time. I would have thought you'd notice the coating but ill have to take the word of those that have been there and done that!
 

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Discussion Starter · #10 ·
I have a few more questions, if anyone can please help.
1) did you epoxy the back?
2) I've got a lot of depth so it's going to be buoyant as ****. Is there anything better to stick it to the back wall with?
3) what percentage do you recommend I thin the epoxy?
Thank you!
 

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No need to epoxy the back at all. Silicone GE*1 is very strong and will hold it to the back no problem. Some of my BG's I have done 10" thick in spots so mine are as buoyant as a life preserver and the silicone holds just fine. Keep in mind that when you make a BG you make it to fit against the back of the tank so the upper trim actually does a lot of the holding down of the BG. I don't go by percentage when I mix DA to thin, but usually just a table spoon to a batch that is about 3/4 of a cup so in percentage that would maybe be around 5%. It doesn't take much.
 

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Discussion Starter · #12 ·
Thank you for your help. I haven't designed it to be physically held down by any part of the tank. Do you think I need to modify it somehow to have that? I was kind of hoping a metric butt load of silicon all over the back would be enough
 

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How will you do filtration? I have mine siliconed in around the edges allowing 1" behind for filter intakes and the returns fit over the lip and background combined.
 

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Using the trim to hold down helps a lot. I won't say you will have issues just using silicone to hold it in, but it will increase the chances of it popping off over time. How do you have it designed right now? can you post a pic of it mocked up in the tank?
 

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Discussion Starter · #15 ·
I'm putting this in a Juwel 450 and it isn't constructed the same way as a lot of tanks with the glass braving around the top of the tank to butt it against. There are a couple of front to back plastic braces but that look like they'd be strong in tension but not really something you'd want to put upward force on. My only real option is to silicon the **** out of the back wall and seal the bottom and outside edges. Unless there's something better than silicon to use as the adhesive?

As for filters, I have a 15 cm x 15 cm void at the back where I will place the canister filter inlet and the heater. This has a sort of hidden rock entrance for water flow from the main tank. I may end up putting a wave maker at the opposite (left) end to push all the tank debris towards this inlet.

Does everything look okay to you guys?
 

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Looks nice! I like a filter at each end, but one works too. Be sure to screen your openings so fry can't get behind. How will you return water to the tank?
 

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First off... Looks really nice you are doing a great job on it. :thumb: :thumb:
If using the top trim to help keep it held down isn't an option then that's not a huge deal you should still be okay. Just make sure to use a good deal of silicone, and while I normally just to the back of the BG, in your case I'd suggest also doing the bottom where it contacts the tank floor as well as the sides. You will probably be just fine and not have anything to worry about, but better safe than sorry. I normally give a few days to off-gas but I'd give it a good week in your case since you'll be using a bit more silicone. The GE Silicone *1 will be strong enough so shouldn't be any need to look for anything else.
 

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Yep that looks like it is probably same thing as GE *1. Says its 100% silicone, I don't see any mention of any added inhibitors, and says aquarium safe so you should be good with that. I normally use less than one tube for a 4ft 75g, but since your tank is a bit bigger and you're gonna use a bit more for the sides and bottom, I'd say get two tubes. You will probably end up using maybe one and a half tubes is even that.
 

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If it's any help, I used 2 tubes (GE1) to install mine and I sealed the back, sides and bottom. It felt like overkill, but I wanted it to stay. I have no top bars for support. It was 72 1/2" x 23" it's been in for 6 months now, no issues.
 
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