# DIY Reef rock deco - need cement experience!!



## beachtan (Sep 25, 2008)

I'm trying to make my own reef-looking rock formations for my tanks. I have 12 and cant find what I have in mind, so I wanted to make my own. I read up on the Garf site and tried several times but just cant get this to harden!!

This last try I used one part quickcrete and 2 parts crushed oyster shell, 1 part pool filter sand.

Still, after 2 days in the mold and 3 days in water, it still crumbled when i put the least pressure on it.

The crushed oyster shell was purchased at a grain elevator /feed store and was sold as chicken feed. But didnt list any additional ingredients. What could I be doing wrong??


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## Stickzula (Sep 14, 2007)

My guess is that the quickcrete you are using already has sand and possibly a larger agrogate in it. By adding all the other stuff too it you are thining it out to the point that there is not enough concrete in the mix to stick to itself and hence it won't cure into a "solid" piece. You might consider omiting the PFS and try it again, or get just cement and add it to your agrogate.


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## beachtan (Sep 25, 2008)

I was trying to find Portland 2 or 3 cement, but the bags were so heavy I couldnt lift them! So I substituted the quickcrete. Sounds like you are right about that. Thank you!

When I leave it sit for the first 24 hours in the sand, how hard should it be at that point? Do I need to handle it carefully?


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## ben1988 (May 2, 2009)

concrete cures in about 36 hours to full hardness


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## beachtan (Sep 25, 2008)

ben1988 said:


> concrete cures in about 36 hours to full hardness


36 hrs in the sand right? doesnt have to be in water before full hardness?


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## Stickzula (Sep 14, 2007)

Concrete needs to be damp, but exposed to air to cure. Leaving the outer layer to crust over will make it flake off, but fully submerging it will make it crumbly.

The best bet is to leave it in the moist sand overnight with a damp towel over it. You could substitute a plastic garbage bag for the towel to trap some of the moisture overnight if you wanted to. Then when you come back to it you should be able to move the piece without a problem. I would, however, leave it covered for a few days giving it a light misting of water from a spray bottle each evening. Then soak it.

The main purpose for soaking it is to get it to release excess carbonate prior to adding it to your tank. This way your pH wont go off the chart killing your fish. It really has very little to do with curing the concrete.

It is also worth noting that some articles suggest soaking it in a salt brine. The theory is that the ions in the salt water will attract the free carbonate ions which, theoretically, make it leach quicker. Some people swear that it works while others report no noticeable difference between the two methods. If it were me, I wouldn't use salt. It may help somewhat, but I would rather go out for coffee a few times than to buy salt only to throw it away after a few days. Just my opinion.

Oh, and you can have the store clerk help you load the cement. The will put it in you car/truck for you. Then when you get it home, you can open the bag and scoop a manageable amount into a bucket and haul it to your work space a bucket at a time. :thumb:

And BTW, pics are ALWAYS appreciated :wink: opcorn:


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## ben1988 (May 2, 2009)

i am pretty sure that chicken feed also has other things added to it for a filler.....
im not sure i am following you on in the water? I would let the concrete set for 36 to 48 hours in the mold and then place it a bucket with some water and see what it does after sitting for a day or so.
I would try one of these two mixtures if all else fales...
up the mixture to 2 parts quickrete, 1 part oyster, .5 part PFS or
2 part quickrete, 2 part oyster


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## beachtan (Sep 25, 2008)

Thank you! :thumb:

I was at Home Depot and there was absolutely NO one who could help me load that massive bag - hate that store :roll: , I always come home with the wrong thing. But your info about keeping it damp helps lots! Thanks!!! So if it crumbles a bit after 48hrs then its not gonna work and I'll need to start over. Got it.

and the info about the "recipe" - thanks!!! I'm gonna try that - hopefully going heavier on the cement will work for me. I hate spending all this time just to see them crumble into nothing!! lol! :x


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## Stickzula (Sep 14, 2007)

the nice thing about it crumbling is that you can just reuse the crumble in the next batch. there's always a bright side  lol


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## Mcdaphnia (Dec 16, 2003)

beachtan said:


> ben1988 said:
> 
> 
> > concrete cures in about 36 hours to full hardness
> ...


In the sand is right, but although pretty hard after a day and a half, for aquarium purposes it should air-cure for 30 days, misting the surface with water as needed, so that the hydration process is more complete. Submerging it in water sooner than a month can leach out very high pH chemicals affecting the tanks water parameters and weakening the concrete.

As to getting the portland cement, most places that sell this also sell five gallon buckets with lids. There are usually some husky clerks around who could pour your bag of portland into two or three buckets so that you could lift it after they load it into your car. Kept dry in a sealed bucket, the leftover cement will last much longer than in the bag it comes in.

One store near us, Home Depot, very recently started selling white portland cement, which has a lower starting pH and makes a much prettier background. BTW, I didn't say husky guys. We used to have pygmy goats and their feed came in 100 pound bags. One of the clerks was about the weight of the bag, but she could flip it around like it was empty.


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## beachtan (Sep 25, 2008)

"but she could flip it around like it was empty."

I'm not a wimp, just have heart problems and am not allowed to lift anything that heavy - pressure could blow a hole in my heart. I HATE always having to ask for help!! so sometimes I just give up. I'm young, so people will look at me like "lift it yer darn self!!" so thats the deal with that.

I'm thinking I'll go to a concrete contractor and ask if I can just pay cash for 5 lbs of the right cement...

So I can reuse the crumbles?! Great!! thanks!


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## Stickzula (Sep 14, 2007)

I don't see why not. just crush it up as much as possible and add it to the new cement. Add it to the mix prior to adding any other agrogate and then you can add more sand, shells, etc if needed.


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## iceblue (Apr 27, 2004)

I built a background using my own mix of Portland type II cement, sand and Perlite that worked out real well. The recipe is on the first page about halfway down this thread.
http://www.cichlid-forum.com/phpBB/view ... highlight=

By accident I came up with something that looks very similar to reef rocks. I had built a basic structure shape out of egg-crate and was using that as a framework to apply a dryer mixture of my concrete recipe to build a free standing wall. As I applied the cement and unbeknown to me some of the dry mix had gone through the egg-crate and fallen behind the structure.

When I finally finished the wall and pulled it out I found these very porous and free-form rock like structures behind it. I know reefers are always looking for ways to build these things that don't involve ice chips or noodles and as I said, these were an accident. If someone were so inclined they might serve well as a base for saltwater live rock. You could substitute some of garf ingredients for the perlite.

Anyways, they do kind of have that coral look you might be looking for.









It worked almost like a cheese grater. As I was applying the mix to the egg-crate by hand (wearing latex gloves) to a thickness of about 3/4" to 1" some of it was falling behind the structure and forming a very porous rock.









A look at the backside of the structure after it was removed.









I don't know if this is what you were looking for but the "rocks" in the first picture do have a nice random and polyp type look to it imo.


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## iceblue (Apr 27, 2004)

By the way. If you can't get somebody to help you lift a heavy bag at Home Depot...... demand, and I mean DEMAND to see a Manager. If the Manager gives you a hassle ( A good one will load it him/herself) then demand to be put in contact with their DISTRICT SUPERVISER. I guarantee you WILL be helped.

I used to work the floor of the Depot as a sales associate over 10 years ago. Their is absolutely no reason you can not get help with a heavy package. NONE. It ticks me off to no end to see where this company has gone since I left. When I worked there, the customer was always, "ALWAYS" first. GRRRRRRR...........


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## beachtan (Sep 25, 2008)

Iceblue: thanks for the boost! I should just make them do it, but I have a hard time with being "helpless" - I like to do things MYSELF! ya know? there are so many lazy people nowdays and I dont want that label!!! lol!!!!

COOL PICS!!!! Thats EXACTLY what I'm talkin' about!! I wanna make a 3-legged table type formation that I can stack onto so the fish have places to go... almost all my tanks are on iron stands with no support in the middle so although I read that rocks are fine, it just makes me nervous to pile them up so I have a lot of open water in my tanks and I like to overstock my tanks so I need more "stuff" in there!! I cant wait to try out your recipe!

Thanks again everyone for all the help - these have been the best post responses i've ever gotten on here! :thumb:


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## iceblue (Apr 27, 2004)

To make the "3 legged structure" out of several pieces of these "rocks" you might try waterfall foam to hold them together. I don't know much about this product but do know that Mcdaphnia is a proponent of this type of foam. Hopefully he'll be back to this thread and can add more esteemed knowledge to the subject.


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## Mcdaphnia (Dec 16, 2003)

That pile of chips through the egg crate reminds me of my wife's spaetzle maker. I better never use it for this! They look great!

What I've done to create stable rock stacks is to mold them in sand, then cover them over except for three or four spots, and build another rock pour on top. Whether they stick together in one assembly or not, the contact points make them stable, and you can start out each rock the same way if you want to create a current under the rock pile to keep out detritus.

Pond foam is good for gluing (maybe call it sticking) lots of things together. Yet if you kept a fraction of an inch thickness of foam between each part, you can saw through the foam if you ever want them apart.


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## beachtan (Sep 25, 2008)

Mcdaphnia said:


> Pond foam is good for gluing (maybe call it sticking) lots of things together. Yet if you kept a fraction of an inch thickness of foam between each part, you can saw through the foam if you ever want them apart.


Sorry but what is pond foam? could I use foam insulation? I tried a piece of white styrofoam but it was almost 2" thick and made of all tiny balls together so when I cut it I had a huge mess and it wouldnt cut straight at all!!

does pond foam cut easier? any big chain stores I might be able to find it at?

one more thing - any pics of the rocks you made? I'm in need of ideas!! especially since all the info I've seen is for saltwater aquariums using these as support for corals etc - and I need them to be able to look good by themselves... :fish:


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## Mcdaphnia (Dec 16, 2003)

Pond foam is like a black colored shaving cream that comes out of a can. Except it hardens into a water safe, sunlight resistant material that will stick to plastic, glass, rock, and other materials you might use in a water lily or goldfish pond, or in an aquarium. It will also stick to hands and clothes so wear gloves and old clothes.


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## ben1988 (May 2, 2009)

again home depot will probably have it....plus side its a small 20oz can....down size it costs like 20-30 bucks here


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## beachtan (Sep 25, 2008)

http://www.quikrete.com/ProductLines/Fa ... eteMix.asp

They talked me into buying this at Home Depot. Now that I'm reading the description, I'm assuming this is wrong and wont work.


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## iceblue (Apr 27, 2004)

What they sold you was a pea gravel "concrete" mix. Take it back and tell them you want a "mortar" mix used for block and brick and contains sand only.


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## bntbrl (Apr 23, 2009)

Great Stuff foam is the same as the pond stuff but not colored. Its 1/4 the price too.


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## Mcdaphnia (Dec 16, 2003)

bntbrl said:


> Great Stuff foam is the same as the pond stuff but not colored. Its 1/4 the price too.


 It is not quite the same as pond foam, sags as it cures and so is harder to work with, coarser bubbles in it, an of-white color which if there is any UV component in your light, turns tan then reddish and finally crumbles into tiny flakes. As the pond foam cures, you can push it back out of sight once it has a dry "skin" on it, while Great Stuff has great expansive force and may resist any pushing you try. Great Stuff may lift apart rocks while or shortly after it cures but is still expanding, and if it goes from end to end of an aquarium, even pop silicone seals or break glass.

However for really large areas, if you allow in advance for its drawbacks, you can use it. For me those are only in pond applications. If you do use the Great Stuff, it should be sealed with a plastic compatible paint after it's finished expanding.


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