# Idea for Foamless Cement background



## gomlin (Apr 28, 2004)

I have decided to make a concrete background for my 125g Cichlid tank. I am going to follow most of the directions I have seen all over the web, with one exception. I am going to remove the foam. I am not interested in having to silicone the background into the tank nor do I have a tank to move my fish into while I wait for the silicone to cure. So I got to thinking of how I could make a foam-free background. I am interested to see if anyone has tried this before or has any suggestions that would make it go better. I am building the foam into 4 sections that I can hang on the back of the tank that will interlock and cover the filter intakes and heaters. My plan is to make the background just like everyone else except I am going to flip the background over at the end and spray a solvent, probably acetone, onto the foam. The acetone will melt the foam and evaporate, leaving the backside of the background concave and mostly foam free. I am then going to add a few heavy layers of cement onto the backside to make a semi-solid background between 1/4- 1/2" thick. I would add a few pieces of stainless wire at the top to be cemented in that I can hang the background from. Being almost totally concrete it will not float and can easily be removed if I want. I do understand it will have to soak a very long time to get the ph lower with the larger mass of cement. Let me know what you think.

Jim


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## frank1rizzo (Mar 14, 2005)

My friend did something similar, but he did not melt the foam. He used a spoon/dremil to scrape most of it away, then added more cement.

The wire idea sounds good.

He just used two large rocks to hold the bg in place.


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## PfunMo (Jul 30, 2009)

Do you have any experience with melting the foam in this way? I have melted foam a number of times by accident and found it was nothing I thought I could control to get a specific depth left. In model railroading foam removal is done a lot and I have not heard of anybody trying to do a controlled melt. I would think you might want to cut or grind it to keep any form of control. It will cut and break out quite easy. My thinking is that cement in the 1/4-1/2 inch range will be quite brittle and prone to break. How about just working a rock into the plan to hiold it down rather than the extra cement?


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## morfeus077 (May 9, 2009)

Great way to get around the problem of doing this for an established tank!

In my mind I see 2 things to contend with, the fist is going to be the biggest issue and that is the rigidity of the concrete as you go to remove the foam. The concrete has little ability to stand up flexing and twisting stress without support. You're going to need to apply the concrete to some sort of support structure that will be permanent. Even applied to foam, I've experienced some cracking when working with concrete DIY backgrounds.

Test this out to see for yourself - take any baking dish and layer some wax paper in it. Then pour in a 1/2 inch of cement that you would use. After 2 weeks, take it out and see how brittle it is... you'd be surprised.

To give you some ideas... Check out how many fiberglass boats are built. They start with a mold and apply a release to it, then apply epoxy paint and then the consecutive layers of fiberglass and framing.

If you could start with a rough form with the foam and apply a fiberglass or epoxy layer that you cover with concrete, you then have your support structure for the concrete.

The second thing to plan is moving all of the water behind the background. If you get pockets that do not move, you'll end up with stagnate water. And another note, if you let the concrete cure for 28 days you should have minimal leaching.


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## mightyevil (Oct 23, 2008)

morfeus077 said:


> Great way to get around the problem of doing this for an established tank!
> 
> In my mind I see 2 things to contend with, the fist is going to be the biggest issue and that is the rigidity of the concrete as you go to remove the foam. The concrete has little ability to stand up flexing and twisting stress without support. You're going to need to apply the concrete to some sort of support structure that will be permanent. Even applied to foam, I've experienced some cracking when working with concrete DIY backgrounds.
> 
> ...


True, the cement will crack and probably break, specially when you try to add the cement in the concave part of it, I just don't think it will hold the weight of the cement. Maybe you can seal the front of the background with resin or something and then do what you want to do...I am not saying this will work but I don't see why not.


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## WillieB (Jul 4, 2009)

Just an idea that might work. Create the foam background and before you apply the first of the concrete, maybe you could cover the foam in galvanized wire. When you etched away the foam mold the wire and concrete would be sufficient to also act as a mold to add the backside concrete.


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## Mcdaphnia (Dec 16, 2003)

Try this. Instead of Portland cement, use enough resin to dampen your crushed coral or sand. Make a mold for each background section -- styrofoam, wadded up newspaper, anything -- and cover it with a release layer of wax paper. Wax paper is about the only thing fiberglass resin won't permanently stick to. Now mix up your "concrete". If you added too much resin, you will get some drips. It is a learning thing. If your background has lots of 3-D, come back and tilt the form and do those later once the first application is dry. A quarter inch thick is all the background needs to be to be very strong.

Leave some holes at the bottom that can be concealed with gravel or tank decorations. That way you can circulate water in or out of those holes to keep it from stagnating behind the background.

An alternate mold that you don't have to remove is Poret foam. Cut pieces to create the 3-D effect and as many concealed surfaces inside caves and ledges as you can. Leave those uncoated, and pump water out from behind the background, and this way the background will also double as a huge biofilter.


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## bntbrl (Apr 23, 2009)

I also think that the cement will be brittle and prone to breaking easily. I was thinking of something beside wire to help strengthen it but nothing really somes to mind right of. Possibly build it using eggcrate andgo from there. Maybe build layers of eggcrate into it as you thinken it but EC is a little thick anyway.

I would think the best way was like mentioned above. Make an epoxy base and use glass or carbon cloth (available at auto body supply shops). You can build a frame temporarily to use as a form. If it were me Id use wax paper or maybe Pam kitchen spray as a release for the expoxy base. using the resin and cloth build up a 1/4 inch or more base before adding cement. It will probably still be somewhat flexible. Perhaps you could use eggcrate while you layer more resin and cloth on to build up some dimension for the rock. If you were going to hide powerheads now would likely be a good time to use eggcrate to make a box to hide it in so that it can be covered with cloth and resin.

Hopefully someone else can improve on this.


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## Mcdaphnia (Dec 16, 2003)

bntbrl said:


> I also think that the cement will be brittle and prone to breaking easily. I was thinking of something beside wire to help strengthen it but nothing really somes to mind right of. Possibly build it using eggcrate andgo from there. Maybe build layers of eggcrate into it as you thinken it but EC is a little thick anyway.
> 
> I would think the best way was like mentioned above. Make an epoxy base and use glass or carbon cloth (available at auto body supply shops). You can build a frame temporarily to use as a form. If it were me Id use wax paper or maybe Pam kitchen spray as a release for the expoxy base. using the resin and cloth build up a 1/4 inch or more base before adding cement. It will probably still be somewhat flexible. Perhaps you could use eggcrate while you layer more resin and cloth on to build up some dimension for the rock. If you were going to hide powerheads now would likely be a good time to use eggcrate to make a box to hide it in so that it can be covered with cloth and resin.
> 
> Hopefully someone else can improve on this.


 I would not use the cloth. The resin and aggregate is strong enough if you make it a quarter inch thick. Actually even feathered (very thin), it is really strong. By NOT coating it with cement, you have no pH problems. If you want to color it, you can use Krylon Fusion paint. I have tried Krylon on it and only had it in use a few months, but it shows no signs of deterioration and this is outside on a pond waterfall in full sun, sort of the ultimate testing ground.


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## Deeda (Oct 12, 2012)

I used Quikrete Quikwall surface bonding cement mixed with Quikrete Portland cement, eggcrate & Feather rock to make my background.

I just determined the number of panel sections I needed for my tank due to the weight of the finished panels & access through the top of the tank.

I used garbage bags to protect my working surface & laid out the rocks on the eggcrate to look natural. Then mix up the cement, trowel into the eggcrate & above the surface, apply the rocks by imbedding them into cement. Filled in between the gaps with smaller pieces of rock & cement. Even applied some sand to hide the white cement in the gaps. Left some of the eggcrate at the bottom of the background uncovered to allow for water circulation behind the background(my filter intakes are behind the background).

Just need to cure the whole setup to allow the alkalinity to subside some. I am very pleased with the result but **** those panels were heavy. I made 3 panels for my 6' tank but should have done 4 panels. Just used silicone to seal the panels to the side tank walls.


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## Rick_Lindsey (Aug 26, 2002)

This is all theoretical, but I considered doing something similar once. I figured I could make the foam/crete background, then sort of nestle each piece down into a sandbox (either your child's if they can do without it for awhile, or use a tray of sand bigger than your piece of background). The sand should support the thin layer of concrete while you melt the foam, then mop out the solvent or whatever, then backfill with more concrete (perhaps concrete mixed with perlite such that the final result is denser than water, but not quite so heavy as a solid slug of concrete). My biggest fear would be that the solvent removal would prove difficult, but otherwhise i don't see any hiccups.

Of course, if you're doing that you could also just sand-cast your background in the first place, though the foam will give you more control if you want fancy shapes.

-Rick (the armchair aquarist)


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## gomlin (Apr 28, 2004)

I tried some solvents on the foam yesterday with some surprising results. I tried several solvents, none of which seemed to have much effect on the foam. Gasoline however worked very well, melting the foam into a slurry about 1/10 of the original foam volume. I'm thinking if I allow the gasoline plenty of time to evaporate, i will probably just seal the remaining dried foam goo into the concrete when I put the next layer on. I was thinking of using the sandbox to support the front layer of concrete while I strengthen it in the back with more concrete. I will post some pics of the progress once I get all the foam carving completed. I was really surprised how labor intensive all the foam forming has been.

Jim


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## bntbrl (Apr 23, 2009)

Im no tsure that I would put that in my tank. I wouldnt use a solvent to eat away the foam and then pu tthat in my tank. Why not use a wire brush or a knife to cut most of it away?


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## Mcdaphnia (Dec 16, 2003)

bntbrl said:


> Im no tsure that I would put that in my tank. I wouldnt use a solvent to eat away the foam and then pu tthat in my tank. Why not use a wire brush or a knife to cut most of it away?


 A local fish distributer used to make backgrounds by splashing gasoline on styrofoam and letting it dry out then spraying it with red, orange and chartreuse DayGlo paints. They were in all the area pet shops for years and no one complained about the paint or the "adulterated" foam harming their fish. The more horrendous the color scheme, the better they sold.

A wire brush on styrofoam would be messy. The particles become statically charged and stick to everything. A knife or a hot air hobby gun would work OK, but the collapsed foam panel becomes styrene plastic as the bubbles inside escape while in a softened condition and the re-hardened plastic would add some support to the background.


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## bntbrl (Apr 23, 2009)

I would think that the gasoline residue would be harmful. I wouldnt think that it would wash away so easily. Maybe Ill try it one day but Id have never thought that it would be okay. Hmmm. I guess you learn something new every day.


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## Mcdaphnia (Dec 16, 2003)

bntbrl said:


> I would think that the gasoline residue would be harmful. I wouldnt think that it would wash away so easily. Maybe Ill try it one day but Id have never thought that it would be okay. Hmmm. I guess you learn something new every day.


 It evaporates. In the meantime the combination is extremely dangerous -- toxic and potentially explosive. The result is OK, but the process is very risky.


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## buffro (Aug 17, 2005)

lay your foam out and slather vasaleen all over it then do your concrete and the foam should pull away however you need to relize that your concrete will need to be thick enough that it doens't break or crack apart when you remove the mold


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## bntbrl (Apr 23, 2009)

Gasoline leaves residues when it dries or evaporates. Perhaps theres not enough of it to be harmful?


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## rarefaction (Aug 6, 2009)

I did this for a reptile tank once. Casting in fine sand worked ok, with a wet smoosh factor. I said I would use crappy plaster if I did it again. You will need to play with the mix of sand to concrete though. I used chicken wire as rebar but I'd go with eggcrate for an aquatic BG.
All that been said, won't it take just as long to cure as silicone? My current BG took about 48hrs to cure, I wouldn't move a cast-crete one that soon...


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## car0linab0y (Aug 10, 2009)

I'm probably late, but I thought about a 3D background for my established tank, and the idea I came up with was suction cups to hold the background to the tank.


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## beaker99 (Apr 15, 2007)

How about using agrocrete. The site below gives directions and the recipe to make it:
http://www.garf.org/MPegs/AragocreteArch.html
and below is another recipe for making backdrop concrete"
I've adjusted the mixture a bit while building the structures but am happy with this formula. 
9 cups portland typeII cement 
3 cups plaster sand 
12 cups of water 
24 cups of perlite

Dry mix the sand and cement together and add 10 cups of water holding 2 cups in reserve. Stir well. 
To this slurry add 24 generous cups of Perlite and mix gently. I use a 1" pvc pipe for this part. It works well and is pretty easy on the perlite. Stir while at the same time pulling up the slurry from the bottom of the bucket. Mix untill the perlite is well covered adding a little water from the reserve to help in the mixing. Careful as you add the reserved water at this point. You want a high slump that will hold its shape to build your structures. To much water and you won't be able to work with it.

For the skin coat I use a mixture of 1 part Type II cement to 3 parts plaster sand. Be carefull here also with the water. Add it a little at a time and mix well. You wan't a mix thats not to dry as it won't stick or to wet as it will sluff off. When I skin the rest of my structure I'm going to add concrete glue to the mix to help with stickiness.

I might also add that as I build these structure in tank a layer at a time. I use a cold moisture humidifier to keep the humidity up. Once I start a structure thier kept in high humidity untill thier done. Usually 3-4 days. I use a bedding sheet to cover the front of the aquarium to keep the moisture in.
And below is another recipe for making concrete rocks:
A Simple Cheap Recipe for Making Cement Rocks
Try this good simple basic recipe to make some of the cheapest porous cement reef rock around. It costs only about 9 cents a lb using this recipe. Using a five gallon bucket, add 5 cups of common easy to find type I/II Portland cement from Home Depot, a hardware store or building supply store. Add 20 cups of crushed oyster shell from a farm feed store. Add 5.5 cups of water and mix very thoroughly with a small hand held flower gardening digger. Use rubber gloves to protect your hands from chemical burning due to extended exposure to the high pH of the fresh cement - this is like soaking your hands in supersaturated kalkwasser! Tip the bucket on a 45 degree angle and rotate or roll it to help tumble and mix the cement well. Use a small gardening hand digger to mix the cement as you tumble it in the bucket. If the mix is too dry add a little more water (slowly). Karen Holt, AKA "The Rocker" tries for a final mix with the consistency of cottage cheese. Others go a bit wetter than this, but not too slushy. You can get crushed oyster shell at a farm feed store. It is used as a very common chicken feed supplement. And that, my friend, is why THIS cement reef rock recipe is so "cheep, cheep, cheep"!


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