# Fake Rock Questions



## KevinS (Sep 23, 2008)

I have some questions about using concrete for fake rocks. I've searched the archives and read a lot about the methods on here, but I still have a few questions. Either I misunderstood or there were some contradictions, but is there or is there not a connection between curing and pH? Lately I keep reading about people using vinegar solutions to neutralize their backgrounds, but I had previously been under the impression that this wouldn't be necessary if the concrete was completely cured. This brings me to my next question-how do you know when it is fully cured if not by checking for pH fluctuations? Finally, since it seems Laticrete is being discontinued, what is everyone using in its place (or has anyone already tried another brand with good results)? Thanks.


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## Link3898 (Sep 18, 2008)

i am not sure about the ph part yet i am still looking into it myself but the concrete i am going to try is a type used in bird baths or stepping stones. and i got it at hobby lobby for now to do a small scale test but i beleive its the same as underlayment cement?


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## melas (Oct 24, 2007)

Curing is one of the most important steps in working with concrete, because proper curing greatly increases its durability and strength. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available. During the curing period-(five to seven days for conventional concrete) the concrete surface needs to be kept moist to permit the hydration process. 

Neutralizing the pH of the concrete is especially important when using it in an amphibian enclosure. Portland cement (the binding ingredient in concrete) has an exceptionally high pH 13-14 and is very alkaline. When fully cured the pH tends to be more like 8-9 which is still way to high considering this is a logarithmic scale! The vinegar finishes the job by neutralizing the carbonates still in the surface of the concrete.

So they are related but are really performing two different functions. Curing = hardness and vinegar (acid) baths = pH neutralization. 

Basically you need to keep the concrete wet for the first week. By combining the acid bath with the curing you can reduce your "down time" while working with the concrete.


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## KevinS (Sep 23, 2008)

Thanks, that's very helpful. Now if I can just figure out what to use since I can't find Laticrete anymore, I'll be good to go.


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## keekalmatter (Aug 9, 2008)

you said to keep the concrete wet while curing for the first week. Is that like letting it sit in a tub of water? or having to go and mist it every so often?


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## melas (Oct 24, 2007)

keekalmatter said:


> Is that like letting it sit in a tub of water? or having to go and mist it every so often?


Either way will work. The two rock walls that I have done have both been submerged. The one was an aquarium so I just filled it with water. The other was an exo-terra so I just laid it on its back in a concrete mixing tub I got from lowes for ~$12.


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## ggazonas (May 11, 2008)

Just so I get this right. First you apply the styrofoam, Then you apply the concrete mixture and once its applied before it dries you submerge it under water for a week. And to neutralize the ph you wash it with a vinegar solution.

Hopefully I'm close


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## melas (Oct 24, 2007)

ggazonas said:


> Just so I get this right. First you apply the styrofoam, Then you apply the concrete mixture and once its applied before it dries you submerge it under water for a week. And to neutralize the ph you wash it with a vinegar solution.
> 
> Hopefully I'm close



Haha! yeah that would work! Be sure to apply the concrete in layers and keep it wet between coats. The first layer should be "runnier" so that the concrete can really get into all of the pores of the foam. Subsequent layers can/should be thicker. 

Spraying the concrete and laying wet towels on it etc will work . . . I just find it easiest to submerge it! This of course wouldn't be feasible with a large wall so then a spray routine would have to be employed.

Good luck!


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## ggazonas (May 11, 2008)

Great that sounds good. And the concrete mix you used was called laticrete which is a type of leveling mortar.

If the wet paper towel thing works well I may just do that. And it you let it cure for 1 week?

This will be my first rock wall and the tank is a 22 cube which will be in my office


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## melas (Oct 24, 2007)

yeah this is what i used for the two rock walls that I've completed. 










honestly for my next one i'm going to try just using pure portland cement and sprinkle a little sand on the last coat for texture. i'm going to sand the surface down when i'm done then. portland cement is CHEAP and i think it will work well. i can't recommend it as i've never used it for this but i think it will hold up for these smaller terrariums no problem! be sure to document your build and share the wealth (pictures)!! haha!


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## melas (Oct 24, 2007)

Oops! Yeah I forgot . . . I cure it for 5-7 days. No rhyme or reason. I just keep it wet until I have time to work on it again.


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## ggazonas (May 11, 2008)

No problem I'll start posting it tomorow if I get to start building it tonight


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## ggazonas (May 11, 2008)

Besides the link to the place online that you provided where else can you buy that polyethene foam?


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## melas (Oct 24, 2007)

dunno . . . i didn't have to buy mine. i work at a server farm and we get tons of it in with all of the IBM servers we get. i would check with a local best buy, circuit city, radio shack etc . . . it's used in packing some types of electronics. with all those new flat panel tv's that people have been trampling each other for it's sure to be in the garbage somewhere! if all else fails go buy some of those pool toy's (noodles)! That's probably the cheapest way to buy the stuff!


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## bgmike64 (Mar 16, 2008)

Did anybody experience cracking in the concrete after or during the soaking / spraying process? Is that normal?


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## melas (Oct 24, 2007)

This is not something I've experienced in either of my builds. I'd be curious to hear more about the what materials you used, the steps you took, and the specifics of the scenario in which the cracking resulted. Do you have any pics? My first thought without knowing any of the details is that you either used way too much water for the later coats or you didn't keep it wet enough during the curing process. Again, without knowing more about your setup it's hard to say.


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## loogielv (Nov 28, 2008)

sounds like it dried out and wasnt' wet enough...
since this thread sorta became about the curing process, i'll continue it and ask a question here:

can you cure the cement in vinegar? just submerge it in vinegar for a week? or does it have to cured in water, and then let the vinegar bathing commence?

also, should you do water changes when submerging it? what about vinegar changes if using vinegar is acceptable?


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## melas (Oct 24, 2007)

loogielv said:


> can you cure the cement in vinegar? just submerge it in vinegar for a week? or does it have to cured in water, and then let the vinegar bathing commence?
> 
> also, should you do water changes when submerging it? what about vinegar changes if using vinegar is acceptable?


I don't think you'd want to cure it in pure vinegar. I'm not sure how much water is in vinegar but I'd be nervous that it wouldn't allow for proper hydration. Also, you need to be careful with pure vinegar as it may actually "eat away" at your concrete when it is still soft. I just let my rock wall in pure water over night and then put enough vinegar in the water to make about a 20% vinegar solution. I did a water change ever couple of days.


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## loogielv (Nov 28, 2008)

oh ok, so cure it for a day or 2 in water, then do a 80/20 water/vinegar ratio or something close to that and then submerge it in that? then do you do water changes at that point, but keep the ration going, no doubt?

ty for the follow up btw


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## melas (Oct 24, 2007)

no worries! yeah that is pretty much what I do . . . can't say that it's the right way or best way but that's what has been working for me. I've done two of them and they are both VERY hard and near neutral in pH (low 7's). Good Luck!


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## loogielv (Nov 28, 2008)

one more question, sorta off topic, sorta on.

i heard about people using slate in their aquariums and that would send their PH through the roof. Would vinegar baths work on slate too? or only on concrete as its curing?


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## melas (Oct 24, 2007)

hmm . . . Slate is a metamorphic rock mostly consisting of clays and volcanic ash. It's comprised mostly of quartz and muscovite. I guess regional variations could include some carbonates. One thing you can do is test the rock you are going to use. Just use an acid test. You could use vinegar for this but is probably not strong enough. Muriatic acid would be a better choice. Buy some pH down (Muriatic acid) from the pet store and put a drop on the rock. Wait 30 seconds to a minute - if it bubbles you have a carbonic rock. I don't know how well a vinegar bath would work to neutralize this or if it could even be done at all. Hope this helps!


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## loogielv (Nov 28, 2008)

lol, i just learned like 15 things in that post, and still dont know what i'm talking about...

so if its a carbonic rock..that means dont use vinegar, or it could? lol. ty btw. repped


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## melas (Oct 24, 2007)

Haha! Thanks! If it's carbonic I would just find another piece. I don't know if vinegar will work. You could always try it. I'd soak it in pure vinegar though . . .for a long time. This is definitely beyond my knowledge or experience so good luck!


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## reptileink (May 1, 2005)

grrrrrr, I am still wrapping my brain around this concept, but my question about just filling the tank was answered...lol 

Great info here guys!


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## clwatkins10 (Nov 15, 2008)

How exactly do you sculpt the rock? Do you let the first layer day and then???


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## melas (Oct 24, 2007)

Sorry just saw your question! I just do the first coat of concrete very thin and watery. This will help the concrete get in all of the pores of the foam (if you are using polyethylene foam) and anchor the subsequent coats. Then immediately before each subsequent coat I wet down the surface of the previous coat with regular water. The second, third, forth coats are much thicker and sculptable. I just used my hands and some paint brush handles. There's really no right way to do this as it depends on the look you are going for (smooth weathered rock vs sharp angular "angry" rocks). Good luck!


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## loogielv (Nov 28, 2008)

i got ONE more question. i know you're supposed to cure it, vinegar etc etc...AFTER it's complete, but what about between coats of concrete?

Lets say i start it and lay 1 runny coat and can't work on it until the next day, do I let it soak in water until time for the second coat?


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## melas (Oct 24, 2007)

yes it really should be cured after each layer. i really didn't use any vinegar until the end but you certainly could if you knew you were going to have large gaps in the time you would be able to spend on it.


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## loogielv (Nov 28, 2008)

you are the bomb! thanks


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## pilo0024 (Aug 22, 2006)

Hey Melas quick q about that curing, couldn't you essentially just put each coat down and then when it's all done soak it and just do it for longer?


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## melas (Oct 24, 2007)

pilo0024 said:


> Hey Melas quick q about that curing, couldn't you essentially just put each coat down and then when it's all done soak it and just do it for longer?


Well you definitely want to keep it wet from the time you place each layer to the time it's cured (5-7 days) - if you do other layers in this time it shouldn't matter - just don't let any layer dry out before it has been "cured" for a week. If you are referring to the vinegar neutralization (not part of the curing process) than yes you could wait until the end and just let it soak for a longer period.


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