Cement vs foam rock backdrop

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dingodan87

New member
I am wanting to convert my tank into a tidepool aquascape creating the look of bedrock or solid rock throughout the bottom and back wall. I hate that the foam is bouyant i dont ever want to have to deal with or worry about my aquascape floating or chunks of it detatching and floating over time. My concern with cement is that can using that much of it crack my glass? Does anyone have experience with this?

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Ive seen complete concrete backgrounds done in glass aquariums i just dont know if the glass was needed to be reinforced in some way

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I made my background out of rocks held in place with sanded grout and lighting diffuser as rebar to hold it all together. There is an acrylic back chamber for filtration equipment, but I'm planning to do this again in a much bigger tank directly to the glass. I don't think it will stress the glass, as long as there is no pressure point.

<a href="https://ibb.co/iJ5bTF"><img src="https://preview.ibb.co/gNLAoF/WIN_20160127_00_29_29_Pro.jpg" alt="WIN_20160127_00_29_29_Pro" border="0"></a> <a href="https://ibb.co/i0PQNa"><img src="https://preview.ibb.co/fvDKha/WIN_20160605_16_11_23_Pro.jpg" alt="WIN_20160605_16_11_23_Pro" border="0"></a> <a href="https://ibb.co/kL438F"><img src="https://preview.ibb.co/d0FAoF/WIN_20170610_17_08_54_Pro.jpg" alt="WIN_20170610_17_08_54_Pro" border="0"></a><br /><a target='_blank' href='https://imgbb.com/'>photos to upload</a><br />
 
Nice. I like using cement as i actually used to make concrete fake rock water features at work so its something im familiar with. I just never worried about any of it being reef safe.. i think filling large voids with expanding foam and just doing a layer of cement on top would be better for both weight and cure time.

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Grout is a cement product, I only used it because I didn't want white or grey and I didn't like any of the black concrete coloring I found. I made the grout about 1-2" thick and it cured enough to move it around in 24 hours. I set it in direct sunlight for a couple days, then submerged it in water for about a month. It was still raising my ph when I added it to the tank. I was able to keep the ph in range with water changes and by adding a bit of vinegar to lower the ph. This whole tank challenges conventional thinking. No sump, no skimmer, diy led light, and worst of all lava rock with antimicrobial sanded grout. Its been up for 1.5 years and while not perfect, I do have softies, lps, and a few sps corals.

I wouldn't hesitate to do this again. I have a 6' 215 gallon that I'm going to set up the same way once I get caught up on my professional life a little bit.
 
Cool. Im definately going to use cement i just want to make sure i use the best kind for my requirements. Everyone loves fast setting cements like quickrete for their fast cure times but i cant sculpt a decent rockwork in under 10 minutes so thats out. Looking at getting some type ii/v portland cement but i cant find anything online about type v being reefsafe or not. I believe type ii and v are the lowest alkali cements am i right? How soon can ph become stable with these cements?? Ive heard type 3 has a faster cure time but i cant find it locally. Ideally id like a regular set time and fast cure time

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Where are you looking for type III? All the big box stores have it here, I've never had a problem getting it.

Cure time till pH is stable will depend on a lot of factors. If it's more than an inch or so thick I would plan on at least 6 weeks.
 
der_wille_zur_macht said:
Where are you looking for type III? All the big box stores have it here, I've never had a problem getting it.

Cure time till pH is stable will depend on a lot of factors. If it's more than an inch or so thick I would plan on at least 6 weeks.
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I live in bc canada. Everywhere seems to just have type 10 or type 1 had to go to a major cement supply store to get type 2/5. Maybe ill look some more though compared to the states we never seem to have anything. I plan on using pond foam to fill in deep voids and then cover with an inch or 2 of concrete. I plan on using 1:2 or 1:3 cement to aragamax sugar sand with rock salt mixed in at the end. Want a bit of a lava rock look to it. May also experiment with adding clumps of rock salt to make little caves and depressions in the rock. Wondering if i should add any kind of bonding agent or something to make it more sculptable. Or anything that could quicken cure time but not set time. When i used to make fake rock waterfeatures we used silica fume to make the mud very easy to work with and sculpt but i dont know how reef safe that would be..though i think its already in cement so maybe its fine?

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Can't really speak to additives, but I've made at least several hundred pounds of man made live rock over the years and your approach sounds fine. I would mix in some crushed coral along with the sand to give a bit more texture, with just sand it tends to look almost too smooth on the surface and it's not as porous. It sounds like you've spent a lot of time making water features so I'm sure you know what you're doing.

Rock salt works fine how you're intending to use it but it does tend to leave very angular impressions, in a reef environment it almost looks out of place in my opinion. When I wanted to make little caves or depressions, I would just put a small handful of plain sand in that spot as I was layering on the cement mixture, then work the cement around the sand. When you're done and the cement is cured, you can rinse the sand away and it leaves a void.
 
der_wille_zur_macht said:
Can't really speak to additives, but I've made at least several hundred pounds of man made live rock over the years and your approach sounds fine. I would mix in some crushed coral along with the sand to give a bit more texture, with just sand it tends to look almost too smooth on the surface and it's not as porous. It sounds like you've spent a lot of time making water features so I'm sure you know what you're doing.

Rock salt works fine how you're intending to use it but it does tend to leave very angular impressions, in a reef environment it almost looks out of place in my opinion. When I wanted to make little caves or depressions, I would just put a small handful of plain sand in that spot as I was layering on the cement mixture, then work the cement around the sand. When you're done and the cement is cured, you can rinse the sand away and it leaves a void.
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Good tip on the sand. What could i use in place on rock salt if you find it doesnt work well? Something more sphearical?

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Something like this
82bc34985dde711a831e6d9b6529423e.jpg
4a166379bd9236d9d792b7a7a5f64b00.jpg


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If you skew the mix heavily towards crushed coral, with only a little sand and only enough cement to bind it, you'll get a nice fine porosity without any dissolvable additive. I've made rock where you could hold a thin piece under a faucet and the water would basically run through it. It doesn't give quite the visible pore structure in your photos though.

I don't really know of any other more spherical additives but I'm sure there's something out there. To be clear, the rock salt works fine, it just leaves a very weird looking sort of too-perfect geometrical surface since the salt pieces are basically perfect little cubes.
 
When i look at those pictures i see a smooth material with many pores. I dont think i can achieve that look with adding coral crush am i missing something

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Reading up on silica fume says it fills in voids making the concrete more dense and waterproof or in my case making my live rock less live. Guess not its not worth it

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Mrs. Music said:
My queen angel nipped the foam millions of times and gave me a million tiny floaters in my aquarium. Talk about ridiculous!
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Exactly why i dont want any exposed foam! Id rather have none in my tank but i dont want to wait a year for my rockwork to cure

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Ok i found a local supplier that literally has every type of portland cement.. now is type 3 really the best for fast curing? Or should i mix it with a low alkali type? So many options..

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dingodan87 said:
Ok i found a local supplier that literally has every type of portland cement.. now is type 3 really the best for fast curing? Or should i mix it with a low alkali type? So many options..

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They only sell in bulk..im at a loss why can i not find anything but type 1 or 10

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