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ejmeier
08-24-2003, 9:14 PM
I have been checking out a european site on ideas for backgrounds, and one of them caught my interest.

You carve a background out of styrofoam and then paint on a layer of concrete and let it dry. It looks pretty cool, the only thing is that the concrete contains limestone (I think?:confused: ) and raises the pH of the tank a decent amount.

Can anyone affirm this pH raise, and if so, by how much? I looked into the pH range tolerances of my fish, and they look like they could handle an increase from 7 to about 8. Anything above 8 would be pushing it...

Inhabitants are:
1 x Tiger Oscar
2 x Gold Gouramis
3 x Clown Loaches

Thanks

ChilDawg
08-24-2003, 9:15 PM
I'm not so sure that Clown Loaches could take a 10-fold increase in pH that well.

ejmeier
08-24-2003, 9:18 PM
It's not like it's gonna be an overnight change from 7 to 8 in the tank. I would acclimate them to the new water conditions slowly.

Anyway, my source for this is wetwebmedia.com , which lists the clown loach as having a tolerance range from 5 - 8. Pretty wide margin of error for pH IMO.:)

ChilDawg
08-24-2003, 9:20 PM
I thought that you were talking about an overnight change...if it's gradual, they'll be okay!

wetmanNY
08-24-2003, 9:26 PM
What if you painted it with epoxy, grayish streaked with tan, then scattered dry sand on it while it was still tacky? Wouldn't you get a similar look?

momopoms
08-24-2003, 9:30 PM
If you could get away with the concrete, is the styrofoam safe for tanks? also, isn't lime in the mix too? just wondering.

ChilDawg
08-24-2003, 9:31 PM
Styrofoam is safe...many foam backings are sold commercially for just such a purpose.

Hebdizzle
08-24-2003, 10:03 PM
concrete CANNOT BE PUT INTO A TANK until it is cured. It can cause a PH of over 9! It must be cured in freshwater for 5 to 6 weeks, with water changes every week. It contains a high amount of lime which easily leach into your aquarium!

I will find a link to prove.

Aaron

Matak
08-24-2003, 10:09 PM
Don't do it!

Concrete, like brick mortar has many more additives than just portland cement, lime, sand and stone that can leach out and are poisonous to fish. Last winter (before I learned about proper fishkeeping) I put in a brick & mortar cave for decoration. My fish began to really get stressed & sick. I lost a couple before I pinned down the source of the problem.

Styrofoam is OK and using a hot knife creatively can give you some really neat effects. You'l have to find a paint that isn't harmfull to fish or styrofoam.

Good luck :)

ejmeier
08-25-2003, 9:14 AM
Sorry abuot the confusion guys, I was intending to use PORTLAND CEMENT. I know that concrete is probably bad for the tank, but the portland cement is practically harmless.

It DOES need to be cured however. It contains something:confused: that I think is limestone-type that raises your pH.

You see, I have a reef background, and I have read all about make rocks out of sand, crushed coral and portland cement. It works great, but you do have to cure it to prevent pH swings...

Hebdizzle: here is one such link of probably dozens if not hundreds more that are out there showing the pH raise in cement: http://reefcentral.com/forums/showthread.php?s=&threadid=60515

wetmanNY - epoxy is too expensive for my budget.:( A $5 sheet of styrofoam and a $5 bag of portland cement, and I'm ready!:)

Matak
08-25-2003, 9:02 PM
Well, I know that concrete (or portland and sand) takes 28 days to reach a 90% cure. Wait as long as you can.

If you make a form, say out of styrofoam, you can really add some relief and texture to the portland sand mix. Just remember, whatever is a knob on the mold becomes a hole in the portland sand mix and vice versa. Try using a boxcutter knife heated by a propane torch and tooled into the styrofoam to give some cool effects like striated layering. Also, if you use a coloured aggregate like a crushed marble or crushed granite, and wash away the surface of the portland sand mix gently when it is thumbprint hard, you can get a realistic colour/texture. Using vegetable oil as a form release before pouring on the portland sand mix will save a lot of headaches when form removal time comes. Pam in the can works best (but buy the no name stuff and save $$$)

Experiment!

ejmeier
08-25-2003, 9:59 PM
So you are saying to release the concrete from the styrofoam when done? I hadn't thoght of that....

I was just going to cut out a decent looking rock pattern in the styrofoam using a long knife, and then melting it smooth with either a hair dryer, or if that's not hot enough, maybe a mini-torch. Then paint on a thin layer of cement - mainly to give it strength, texture and color - then put the entire thing, styrofoam and all in the tank.

Matak
08-25-2003, 10:05 PM
I'm not 100% sure but I think if concrete (or any portland based product) is "flash cured" it loses a lot of strength and can get shaly.

Yeah, about the stryrofoam idea, I was suggesting using the stryrofoam as a mold, like for plaster of paris.

ejmeier
08-25-2003, 10:34 PM
Originally posted by Matak
I'm not 100% sure but I think if concrete (or any portland based product) is "flash cured" it loses a lot of strength and can get shaly.
What is a flash cure? If you are thinking of the mini-torch, that will be used BEFORE the cement. It is to melt out the roughness that the knife will leave behind in the syrofoam. (You know how crumbly a bare edge of styrofoam can be.)

I was planning on actually putting the background in either a large basin or bucket, and changing the water every once and a while, or simply putting the cement in a nearby creek. This would wash away any lime that is in the water, and the large volume of water would nullify any pH increases during the curing.

I think I will just paint the thin layer of cement as opposed to the mold technique. It will be much lighter, and less cement will be used, so in the event that something bad does happen, it won't be as severe because there is less of it in the water.

Matak
08-25-2003, 10:37 PM
Ahhh, I see now. I thought you were going to speed dry the cement with the torch. My dumb.

I thing the creek idea is best. Constant water change. Maybe a 24 hour brine bath after the creek baptism to disinfect before introducing to the tank?

GoLdFiSh_GrL
08-25-2003, 10:42 PM
wut he sed. LoL! no1s answering my post so i'm just chatting here while i wait.

wetmanNY
08-25-2003, 11:18 PM
Just chatting while you wait? Indeed. Forty-four posts in the first day?

Isn't this your bus? Let me help you on it.

(Why is Sting glowing? Must be orcs about.

carpguy
08-26-2003, 12:14 AM
I'm still not 100% clear on the curing business, but I'm finding much shorter periods posted on various concrete sites than I'm seeing here. I think we ought to take the relatively small volumes of concrete we're talking about into account, especially with regards to a skim coat technique. There are also differences in curing time between concretes, and there are quick-curing concretes (and chemical additives of uncertain consequence).

The concrete examples for aquaria I've seen on the web all seem to be used in salty or in Rift Lake Cichlid tanks. For soft and acidic folks like myself there may or may not be a workaround. I'm going to see what I can do about running a few experiments over the next few weeks and will post back my results. Anyone actually know some of this stuff up front? There seems to be a knowledge base behind more than one of the posts up here…

I have managed to work out this much so far (thank you mighty google (http://www.google.com))… A good cure effects the ultimate strength of the concrete (and we're not using it for strength). A bad cure may result in aesthetically bad results, like cracking and flaking. The cure is a chemical reaction within the concrete called hydration. Hydration likes water, and curing fully submerged isn't a bad thing for the concrete (probably a bad thing for most of our finny friends). One of my most basic questions is this: how reactive is the lime before and after the cure? Is the lime "locked in" after the cure and less able to drive pH up (and if not, why doesn't concrete dissolve)?


Originally posted by ejmeier
I think I will just paint the thin layer of cement as opposed to the mold technique. It will be much lighter, and less cement will be used, so in the event that something bad does happen, it won't be as severe because there is less of it in the water.

I've been looking at a thin layer approach (http://www.btinternet.com/~colinlewis.bonsai/Reading/Cement.html) applying a series of light coats to a wire mesh and styrofoam armature, mostly for the weight. Another approach that would work for a mold would be to build up the concrete in layers in a mold until you had a substantial shell and then filling that with expandofoam (good support and nice and light).

Anything bad thats going to happen is going to be much more a function of surface area than of total mass, and thin layer approaches won't reduce that.

terror
08-26-2003, 4:57 AM
interesting topic..

i have some questions.
what is the best material to use to make ponds..
if cement is used. will this cause a high ph?
what if the pond is painted with a waterproofing paint. will this prevent the high ph?
how about installing tiles to the pond?

what is the purpose of curing? and what procedures are involved with this process??

Matak
08-26-2003, 7:24 AM
I have been corrected. If I recall correctly (I'm in the trowel biz) concrete is 90% cured in 7 days and 98% in 28 days. It never really fully cures, even after 100 years, but the rate of cure gets progressionally less as time marches on.

The only paint that I have seen that actually remains stuck to concrete over time is an epoxy based paint.

If the portland sand mix leaches out, then covering it with anything inert will cure this problem.

I am quite curious to see Carpguy's test results. What would you be testing for?

ejmeier
08-26-2003, 8:54 AM
I think for our application we have to get our terms straight.

I am going to let the cement HARDEN for one or two days (possibly longer). This is just to allow it to get enough strength so that it won't crumble or break.

As for fully CURING, I am not concerned about this, as long as it is sufficiently strong in my tank.

What I do think is important is LEECHING most if not all of the lime out of the cement. This is done by soaking it in water continuously, and changing the water once it becomes saturated with lime - usually a film appears on top of the water. (NOTE: this is not the same as CURING because to cure it has to be dry, whereas to LEECH it needs to be wet.)

So I think we're talking about two different things - to CURE the cement to the point where it is strong enough to use, and to LEECH out any lime so that it is aquarium-safe.

Disclaimer: Uhhh, I pretty sure that what I am saying is right...:confused: but I could be wrong.....


.....maybe....;)

Matak
08-26-2003, 5:08 PM
Welll, hardening, curing and lack of leaching are all about the same thing. The leaching occurs when any soluable solids become waterborne and leach out of the concrete. This will happen less and less as time goes on. Again, the tests Carpguy plans to do should prove interesting.

ChilDawg
08-26-2003, 5:44 PM
Originally posted by wetmanNY
Just chatting while you wait? Indeed. Forty-four posts in the first day?

Isn't this your bus? Let me help you on it.

(Why is Sting glowing? Must be orcs about.

Just got that...very subtle, WetmanNY.

carpguy
08-27-2003, 9:07 AM
Originally posted by ejmeier
I think for our application we have to get our terms straight…
I am going to let the cement HARDEN for one or two days (possibly longer).…

As for fully CURING, I am not concerned about this…

What I do think is important is LEECHING most if not all of the lime out of the cement…

(NOTE: this is not the same as CURING because to cure it has to be dry, whereas to LEECH it needs to be wet.)

So I think we're talking about two different things - to CURE the cement to the point where it is strong enough to use, and to LEECH out any lime so that it is aquarium-safe.


This is exactly the area where I'm dissatisfied with my googling.

We obviously have to let the concrete harden enough to be able to move it and manipulate it, but curing as a process is going to start on its own schedule. Two or more days in and its taking place with or without you.

My googling (no actual experience here) has revealed that curing is a process -- hydration -- that chemically changes the concrete. Concrete doesn't just dry, there's a chemical reaction that takes place and this reaction requires water. To cure properly it doesn't need to be dry. It shouldn't be dry. An overly dry cure will result in cracking and possibly flaking or crumbling. We don't really need to worry about strength, but we do need at least a decent cure to avoid cracking.

After this chemical change is the lime free to dissolve out into the water column or is it locked into some bond? What sort of pH havoc should we expect from cured concrete? (Those of you who are chemically inclined should feel free to jump in here :D )

From what I have been able to sort out, the lime (calcium oxide) reacts with water to form calcium hydroxide, which is still basic but much less soluble and reactive. I think this may be a dangerous addition to a CO2 enriched planted tank, since calcium hydroxide will react with CO2 to form calcium carbonate :( . Maybe not as much of a problem in a regular tank.

I'll try to have something setup by next Wednesday or Thursday and will start a thread on it in DIY. So far I was thinking of something like this:
Using two different concretes (a grout and a more normal Portland-type) I'll make 4 regularly sized bricks (2 of each). 2 go into separate water containers (maybe 5g tanks) to cure submersed with water changes, and two are cured wet with towels, submersed once or twice a week to get readings. I'll measure pH, GH, KH, temperature vs. a control, and size (expansion). After a few weeks of this I'll coat all 4 with epoxy and test 2 in plain water, 2 in CO2 enriched test tanks.

Any thoughts, comments, suggestions?

This has been on my mind all summer and I feel like its time to get it sorted out…

ejmeier
08-27-2003, 9:56 AM
That's WAY more than I would ever be willing to do.:D

I would agree that the lime that is leeching out of the cement could be harmful for tanks with a high CO2 content.

Here is about all I know on the subject in regard to MARINE applications:

Most people will let it "cure" (or whatever you want to call it) fully submerged for six weeks. This is the time that most people have found to be sufficient. By sufficient, I mean that if you put the cement in water, it will not raise the pH (which is presumably from the lime content that leeches out - water saturated with calcium hydroxide has a pH of around 12). So once all of the lime is done leeching out (no more pH increases observed) then the rock is "safe" to put into the tank - (but cured, I have no idea...)

You can also speed the process by using an acid instead of water. I have heard of people using muriatic acid in there cure baths to speed the process - it shaves off maybe a week or two.

Hope this helps.....

PS - If you want a good way to cure a small rock with a lot of water changes - put it in the tank of a toilet (the top part). Every time you flush it gets close to a 100% water change, and its so easy...:)

carpguy
08-27-2003, 12:49 PM
If you watch us poor New Yorkers operate for a while, its all about maximizing the available space.

I like plants and I like loaches. Small tanks fit in small apartments, space is always at a premium.

So what if I built a caveworks that could double as a series of terraced planters, got rid of those pesky rocks taking up good floor space…

Unplugged the TV, got all the time I need.

Matak
08-27-2003, 9:50 PM
Carpguy, you could achieve that with a slurry of natural aquarium gravel and safe epoxy. Just add enough mixed epoxy to make the gravel slightly wet, then either apply the mixture over pvc tubes or pour it into molds. You can clean whatever tools you use with acetone.

carpguy
08-27-2003, 10:21 PM
I've been looking into a few different methods including epoxy with sand, synthetic resin with sand, etc. They mostly seem like they'd be better for molds than for modeling. Trial and error. I've got a few mold ideas as well.

The concrete bit has been floating around my head a little while now, so its mostly curiousity at this point. From what I've been able to sort out so far, its probably not a good idea for my kind of tank.

This is for aesthetics and a custom fit. I'm not trying to save time or money. I'm trying to spend time and money -- carpguy at play. I'm looking to set up a ridiculously nice pair of 30s. Apartment living: think big, work small.

If I can come up with something I'm happy with I'll post it. I think its about time I move past the drawing board.

If it weren't for these d@M& forums I'd probably have just put a little tank on an end table and have been happy with it. You folks keep putting ideas in my head :D .

Matak
08-28-2003, 7:11 AM
That's what were here for ;)
If you want any help or advice on working with epoxy & stone just ask. It's what I do (http://www.sierra-stone.com/) for a living.