Cement vs foam rock backdrop

[karimwassef]

I went concrete on mine. Looks ok

https://youtu.be/UDS1lxLRWyA

Concrete allowed me to create ledges and overhangs that were structural.

Here it is a couple of years later

https://youtu.be/C6YSpSPNwd0
https://youtu.be/qpUkbAJNyFw

I cheated though and used white pumice to make the rock work lighter. Also used PVC pipe as the backbone.

I have a few threads on the build and results. Here's the main one (I call mine "clothcrete"):

http://www.reefcentral.com/forums/showthread.php?t=2391044&highlight=clothcrete

 

[der_wille_zur_macht]

How does crushed coral create voids if it doesnt dissolve

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A concrete mix with very little sand and cement and lots of aggregate in it will naturally be porous. The cement is basically just gluing the other particles together, it doesn't by default fill voids between particles - that's what the sand is for, basically. A pile of crushed coral is porous - the chunks are big and jagged and there's lots of space between them. A mix of cement, a little sand, and crushed coral retains that porosity, because there isn't enough sand or cement in the mix to completely fill all those voids.

 

[ericarenee]

A concrete mix with very little sand and cement and lots of aggregate in it will naturally be porous. The cement is basically just gluing the other particles together, it doesn't by default fill voids between particles - that's what the sand is for, basically. A pile of crushed coral is porous - the chunks are big and jagged and there's lots of space between them. A mix of cement, a little sand, and crushed coral retains that porosity, because there isn't enough sand or cement in the mix to completely fill all those voids.

You can also mix in some rock salt small pieces .. then soak the pieces in water with pump going and the rock salt will dissolve leaving even more voids and surface area

 

[dingodan87]

A concrete mix with very little sand and cement and lots of aggregate in it will naturally be porous. The cement is basically just gluing the other particles together, it doesn't by default fill voids between particles - that's what the sand is for, basically. A pile of crushed coral is porous - the chunks are big and jagged and there's lots of space between them. A mix of cement, a little sand, and crushed coral retains that porosity, because there isn't enough sand or cement in the mix to completely fill all those voids.

Ok i understand just not the look im goin for. Finally got my hands on some type 3. I was going to use mostly dead live rock and fill voids in but in playin around with my pieces im not impressed. Gunna need some creative inspiration and just go nuts with the concrete

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[dingodan87]

Cant even get nice lookin dry rock in canada it all sucks! I ended up buying some live base rock because it at least looked real but it was still 3$/lb!! Really wanted some brs dry fiji but they wont ship it here for some reason.

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[dingodan87]

Im rambling cuz i have no one else to talk to about this stuff. Im happy were not takin rock from the reef anymore but man i used to love browsing through the live pieces at the lfs they were works of art.

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[karimwassef]

porosity isn't critical IMO.

<a href="http://s1062.photobucket.com/user/karimwassef/media/219F4CD1-1F55-46FB-B9B4-4D1BCB4B1C94_zpsjddkrorg.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/219F4CD1-1F55-46FB-B9B4-4D1BCB4B1C94_zpsjddkrorg.jpg" border="0" alt=" photo 219F4CD1-1F55-46FB-B9B4-4D1BCB4B1C94_zpsjddkrorg.jpg"/></a>

 

[dingodan87]

Back on topic i got it for creating sphearical voids in the rock.. candy??? Like balls of hardened sugar?.. why not?

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[dingodan87]

porosity isn't critical IMO.

<a href="http://s1062.photobucket.com/user/karimwassef/media/219F4CD1-1F55-46FB-B9B4-4D1BCB4B1C94_zpsjddkrorg.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/219F4CD1-1F55-46FB-B9B4-4D1BCB4B1C94_zpsjddkrorg.jpg" border="0" alt=" photo 219F4CD1-1F55-46FB-B9B4-4D1BCB4B1C94_zpsjddkrorg.jpg"/></a>

Not critical just the look i want. Ever seen a hawaiian tide pool? Pretty cool

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[der_wille_zur_macht]

Back on topic i got it for creating sphearical voids in the rock.. candy??? Like balls of hardened sugar?.. why not?

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And if any of it gets left behind in the rock, it's like built in carbon dosing!

Give it a try on a small piece and see what happens. I don't see why it wouldn't work but I'd be sure you know that it's all dissolved and the rock is clean before you use it.

 

[dingodan87]

And if any of it gets left behind in the rock, it's like built in carbon dosing!

Give it a try on a small piece and see what happens. I don't see why it wouldn't work but I'd be sure you know that it's all dissolved and the rock is clean before you use it.

Thats what i thought.. im gunna run fresh water through the tank for a few weeks anyways so as long as whatever i put in the rock is biodegradable i dont see an issue

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[der_wille_zur_macht]

If you don't care about porosity and only want the texture on the surface you could just press the candy (or whatever) into the cement after you're done shaping it. That should make it much easier to get it all out of the system, versus wondering if some of it is still buried deep in the rock.

 

[karimwassef]

My experience is that all "impurities" degrade the strength of the matrix.

I tried salt, foam spheres, rock sugar, baking powder, etc... it's all terrible

Rocks should have cavities, not porosity. I achieved cavities by using PVC backbone with holes drilled into it.

 

[dingodan87]

My experience is that all "impurities" degrade the strength of the matrix.

I tried salt, foam spheres, rock sugar, baking powder, etc... it's all terrible

Rocks should have cavities, not porosity. I achieved cavities by using PVC backbone with holes drilled into it.

Can you elaborate? Why was it terrible?

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[karimwassef]

it results in a weak structure that breaks down. It may happen quickly or later on, but the strength of concrete is gone.

Salt is especially bad. I'm not sure why.

 

[der_wille_zur_macht]

Outside of some of my initial experiments that were obviously poorly done, I've never had a DIY rock break except in extreme circumstances (ie I hit it with a hammer and cold chisel trying to break it on purpose). Some of my rock has been underwater for 10+ years. I don't think porosity in and of itself is going to limit the strength. How you get the porosity and how good your mix ratio is to begin with probably has a lot to do with that, of course.

 

[dingodan87]

Too bad about the sea salt. I picked up some hard candies and im going to experiement with a couple rocks using those and/or bits of styrofoam. We will see what happens. I found some pics online of beautifully done fake lava stone but no information as to how they were done. The pores should be random sized and spaced pretty evenly from what i see in pictures of the real thing.

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[karimwassef]

Maybe small balls of wax and then put it in an oven?

My rockwork is 4 years old - no issues. The cloth fiber acts as reinforcement and the pvc skeleton allows them to be connected like legos with standard connectors. They're structurally strong enough to hold a lot of weight too.

The open PVC cavities inside create a safe refuge for worms, sponges and pods. I've even had cleaner wrasses back up inside the tubes.

Using white pumice made the structure very light too. The videos show some of that I think.

 

[dingodan87]

Cant put it in oven as im sculpting directly in tank. Thinkin about air entrained concrete. Ussually the air bubbles are very small with commercial additives but maybe i can modify it. Larger air bubbles in concrete are something most people tirelessly try to eliminate not much information on how to encourage it

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[NewToReefHobbby]

A local LFS chap suggested me to use this product. It is used in ponds, etc and its fish safe - https://www.amazon.co.uk/gp/product...fl_title_73?ie=UTF8&psc=1&smid=A3P9O9FZTPIIYP for the back wall. and to make it look much more natural, couple of ideas -
1) once its almost half way through drying up insert different shapes of rocks/stone and you can install frags later on them
2) once its dried up, apply a thin layer of silicone (same used for building fish tank) and then dip the whole thing into the sand, and any excess it will come off once its all dried up. apply frags as you want.

my 2 cents