The Ultimate DIY Rocks!

[SpankythePyro]

Only prob is I want a cheap aggregate and I do not want to weaken the rock with salt as I will be steaming this rock. Oyster shells get a bit heavy, crushed coral even more. I am going to texture the outside with dampened sand.

Don't we want to harbor bacteria?

edit: Is quikcrete play sand good enough as well? It does contain silica/quartz

[big400g]

Portland Cement is cheap especially if you go with the normal not the white cement, use aragonite, crused coral I would not use play sand. Play sand seems to have smaller fines and looks like it has more dirt. Make your mixture form the rocks, and press whatever you want in the outside for looks. Maybe use a dowell to press in holes.

[goldmaniac]

Originally posted by big400g
As mentioned by a few here, I would not use perlite. It could harbor bacteria if not mixed in right, plus the weight is not really an issue, some weight is good to keep them down and stable. As for the use of refugium sand you will need to thoroughly clean your sand before using it. The detritus will weaken the rocks.

Use the sand for the main mixture of the rocks and the crushed coral to the outside of the rock for looks. A good mixture should be 1:1:1 using larger than rock salt.

I like to use lime in my concrete it makes it more of a clay consistency. I am not sure the effects of the higher lime concentration in our tanks but it could be good.

Big400: you use that 1:1:1 ratio?

Refugium sand: I found that detrious doesn't really get caught up in the sand, I think it's a non-issue. just pull out the sand or substrate, put it in a bucket, swish it around with some fresh water, pour off the suspended detrious, and do it maybe once more. Then let the sand/substrate dry. done.

I haven't noticed any weakness in any of the rock after my first batch when I used too much rock salt that was also too large of pieces of salt. When large pieces of salt melt away, it weakens the rock too much.

When using smaller rock salt - ideally 1/4" pieces and smaller - the bridges I was making could handle me standing on them, even with sand or other substrate. I'm 180 lbs.

I agree that the lightness of perlite was an issue. without perlite, my rock is so pourous and holey (holy?) that it was certainly light enough for the tank, much lighter than Wild live rock.

again, just my $.02

-----------------

SpankyThePyro:

I made arches by using mail crates, and going layer by layer.

- make a layer of salt in the milk crate
- add four golfball-sized piles of mixed cement.
- fill in the milk crate up to the top of the piles of cement
- add more cement to the piles
- fill in the milk crate a little more, again to the tops of the piles of cement.
- add cement again, repeat.
- when you want to connect the 'columns' of cement you're making, just pile a line of cement from one column to another
- fill with salt up to the top of the cement, again
- repeat
- repeat
- etc.

I found that I could fit two of my bridge structures in a milk crate, each with four 'legs' and accompanying bridges between the legs, and get it done in an hour's time, including the making and clean-up of the 5-gallon bucket of mixed cement.
I used latex gloves and wore a mask.
The footprint of the four columns came out to make a lower-case y. this way, I could make two at a time in a single crate.
I can stack my bridges upside down, sideways, crooked, whatever, and they always seem to look good. People notice the holes the fish swim through but never the actual pieces.

[goldmaniac]

I'm looking back at my posts and see that this doesn't make sense:

Originally posted by goldmaniac
Found my entry from 2008:

"I like a 1:1:2 ratio of cement: tank sand : Mortons Water Softener salt found at Lowe's or Home Depot, blue bag."

looking back, I'd even reduce the salt ratio to a little under 1. My first batch resulted in a few pieces crumbling over the years.

so I'd go with this ratio: 2:3:2 portland Cement:tank substrate:salt

hope this helps

I mentally leaped thinking that the Salt ratio was started at :1 instead of :2

My suggested mix: 1:1:2 or maybe even 2:2:3 (by volume) of Portland cement:sand:rock salt if the granules of the rock salt is more than 3/8". larger salt rocks make weaker points in your MMLR when it all melts away.

[SpankythePyro]

Originally posted by big400g
Portland Cement is cheap especially if you go with the normal not the white cement, use aragonite, crused coral I would not use play sand. Play sand seems to have smaller fines and looks like it has more dirt. Make your mixture form the rocks, and press whatever you want in the outside for looks. Maybe use a dowell to press in holes.

argonite sand gets expensive!

So you used a milk not mail crate, and you basically used the salt as a filler? As you added more concrete you added salt around it? The added more concrete.

I'm at a crossroads here lol. I might just used Calcium Carbonate (chicken grit) instead of sand.

[goldmaniac]

I'm Sorry - MAIL crate. U.S.P.S. crate.

What I'm picturing as milk crates have holes in the bottom. Mail crates around here do not.

yes, i used salt in the cement mix to make it pourous, and also used rock salt as filler in the mail crate.

Chicken grit sounds fine. I'd give it a rinse ahead of time, but otherwise it's good to go. calcium carbonate is okey-dokey.

This is why I recycled the refugium sand and used it in the mix. It's free, it's safe for the tank, and i know where it's been. And it's free.

\ if another of my fishtank projects is going to take up my time, it better be a bargain!!

And I found that when using rock salt to surround the cement as it dries, it creates a texture on its own and you don't have to push substrate onto the surface for a nice look.

[goldmaniac]

Here's a picture of the last batch of live rock, Freshly introduced into the tank so you can see how the White cement looks -

keep in mind - this is freshly added MMLR

April 2008

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more pictures by clicking my Red House

[darkdruid]

I have a question about adding something to the rock to make it lighter and more porous. How would adding shells work? I don't mean crushed shells, I mean empty snail shells, astrea, nerite, cerith, nassarius, etc. Between me working at a wholesaler and collecting my own, I have bags full of them. The empty space in the shells should really lighten up the rock with nothing to desolve like salt or pasta. Not to mention that any showing on the surface of the rock would look cool. Is there any reason it wouldn't work?

[SpankythePyro]

I just got chciken grit but it says its made of granite? How would that work as granite is a silicate?

EDIT: yea granite grit doesn't work.

Also I'm still looking for sand, don't really want to buy "aquarium" sand, anyone have any alternatives?

My oyster shells are also very small, are they supposed to be the size of say an pencil eraser? lol

[rguyler]

You can use silica sand. Randy Holmes-Farley couldn't confirm any truth to the leaching myth and there are many people on RC who use it with no ill affects. I personally don't like it in my tank because it scratches the glass very easily but being a component of your rock will make that a moot point.

[SpankythePyro]

Hot dayum! Can anyone else confirm this? I want to use some Quik-crete play or multi-purpose sand, I already have Calcium-Carbonate to buffer the water in the form of crushed and dusted Oyster shells.

Here are pics of my oyster shells

[rguyler]

I was vague and technically inaccurate in my previous post so please let me explain in more detail.

Randy Holmes-Farley in the past has admittedly argued against the theory that silica sand will release silica in the water. However after some basic testing he found that his play sand sample did indeed release silica. in the end he states that it's impossible to say what your results will be and that using silica sand really won't be a problem as numerous organisms will consume silica, such as sponges and mollusks. In fact he doses silica in his tank.

In this case, the sand will be embedded within the concrete and won't be readily exposed to water in large surface areas so the exposure to water will be minimal compared to a sand bed. A couple of things that Randy alludes to that may help is to rinse the sand really well, especially with RO water and choose the lightest colored sand as possible as it will have a higher concentration of quartz. So the bottom line is that "play sand" may not be okay but a good quality silica (quartz) sand should be fine as substrate. In your DIY rock? Use your own judgement but even the play sand should be fine. Plenty of people used it in various DIY rock posts.

BTW - I think it was in this thread that this was discussed at length but maybe not. Either way, you'll find many people using silica sand with no issue.

[SpankythePyro]

hmmm ok, i wish i could find that part of the thread. Dunno what kind of sand to use then other than play sand.

Still waiting on feedback of my pulverized oyster shells. I'm going to try this tomorrow though

[big400g]

To clarify, I have not yet done any aragacrete, but I do tons of high performance concrete every day. My comments are about how to produce good concrete and I do not know as well as some on here the visual effects of salt or shells...

I personally like the Quickcrete sand that is sold in 100# bags, it is white in color and has a nice uniform grit. it helps to lighten the color of the concrete and gives you a uniform grit for quality concrete when the concrete is thin.

As for shells, you have to be careful as some shells are very smooth and the concrete will not adhere well to them, also the size of a shell could create a weak point if the surrounding concrete is not thick enough.

just my 2 cents, again I am on this thread becasue I want to build my own rock as well. I respect the knowlege and experience of others here and appreciate you telling me how you did yours.

[SpankythePyro]

Yup I value your input and everyone elses here too. I am not afraid to ask questions as you see.

The 100lb back of Quickcrete sand, what is that? I've found 40 and 50lb bags.

In addition I will test this tomorrow but my oyster shells are more like crushed coral than actual oyster shells...

There is alot of dust in their too. Should I was it out or leave it in for the mix?

[rguyler]

Here is what I believe is the last "how-to" post from Insane Reefer. She is the BOMB when it comes to making rock so If you want to make good rock then read this thoroughly. Too bad she's no longer active on the forum like she was...


By Insane Reefer -

v9.0 FINAL VERSION: Aug - 14 - 2008

Hey All,
These are my favorite tips and links so new people can find it all pretty easy. It is a summation of the most commonly asked questions and things I have picked up through making my batches. Some I’ve gleaned from this thread, others I’ve learned from past mistakes and experiments. I've been making DIY man-made rock or aragocrete off and on for close to 8 years, though I learned about it from the pre-internet BBS's back in the very early 90's. Lately, I have even made some money on my rocks.

THIS WILL BE MY LAST MLR POST


This does not contain any information on "Jiffy Rock", the new method I am working on to produce rock in under a week or 10 days. This only pertains to traditional rock methods.

I thought I’d pass this info on – maybe save someone some frustration or spark a new idea.


First, good info can be found at these two places - I think everyone who wants to make rock should read these in full. One of the articles gets pretty heavy handed with the science/chemistry aspect, the other babbles on tangents once in a while, but both are worth the read, IMO.
ARAGOCRETE RESEARCH BY TRACY GRAY
Reef Propagation Project


List of Appropriate Aggregates

Sand - Sand makes cement stronger, so is something you want to add to your cement. You may also find that sand is a great casting medium and that you can get crazy shapes with damp sand. Any “clean” sand will work – look for darker grains which could indicate heavy metals and avoid these sands. Whatever you choose, keep in mind that the smaller the grain size, the less obvious it is on the rock, but for sand for use in the cement, you want a larger particle size, if possible.

Caribbean/aragonite is “best” for adding to the mud, but very hard to find at a reasonable price.
Play Sand is generally fine to use - most play sands will be made of quartz and so basically inert.
Limestone Sand/Pulverized Limestone has gotten good results as a DSB, so should also work and can be found at some Big Box Stores like select Home Despot's.
Glass Sand is a new product on the market that is made from recycled glass - this would also be an excellent choice and might encourage quicker coralline growth.
Calcium Carbonate for “Feed Mixing” (AKA Aglime, Chicken Grit, Scratch Sand), comes in a range of textures and grain size – from sand to gravel like CC. Most real feed or farm supply stores will carry it in some form, and for less than $4/ #50, but make sure it is the calcium based stuff and not granite based – it should have a percentage of calcium printed on the bag – if not, it might not be the stuff you are looking for.
Dolomite Sand – Same as Calcium Carbonate, just another name (and slight chemical variation) and is just fine to use - you might find it as "Aglime" at the farm supply store.
Sand Blasting Sand can also be used (and works really well as casting sand) and is sugar fine, look for "Unimin" Brand, or any that says it can be used for filtration – this will be 99% pure Industrial Quartz.

Crushed Coral - AKA "CC". Makes nice, realistic rock with a high over-all calcium content, but it is expensive.
Crushed Oyster Shell - AKA "OS". Any shell will work, but OS is very cheap at feed stores.
Perlite – has a pore structure similar to CC, but much, much cheaper – great for making light weight rock. It is basically inert, puffed glass. Make sure that the perlite you choose does not have any fertilizers added to it – most do not, but a couple do.
Salt - Many thanks to Travis L. Stevens for figuring this out! The salt of choice is "Solar Salt Crystals", typically found as a Water Softener Salt. 99% pure salt. Get the coarsest crystals you can find. Solar Cube can be used, but is sort of chunky - makes nice holes though. Boiling the "cubes" rounds off the edges and makes nicer holes. Solar Pellets can also be used, same as Cubes. Look at your grocery stores or wally-worlds if your local hardware doesn't have what you want.


Rock Recipes
Ingredients are measured by volume, not weight!

Travis’ Original “Salt Rock” Recipe: 4:1 or 3:1 / Salt:Cement
Improved? “Salt Rock” Recipe: 3:1 or 2:1 / Salt:Cement
Ol' Skool Recipe: 1 to 1.5 : 2 :1 / Cement:CC&OS(mixed – or use perlite&shell mix):Sand
Ol' Skool + Recipe: 1: 1 to 1.5 : 1.5 :1 / Salt:Cement:CC&OS(mixed – or use perlite):Sand

I prefer the "Ol Skool" recipe, but I use a variation with perlite. Makes excellent, porous rock. Keep in mind that even though the original “Salt Rock” recipes do not have sand listed, your rock will be much stronger if you replace a portion of the salt with some sand. On the “Original” recipe I’d use 2 sand and 2 salt to 1 cement.

It is highly recommended that you do not make “Salt Rock”. Salt is horrible for cement, and over the last 6 months, I’ve had more and more complaints coming in about failed, crumbling rock, and guess who gets the blame? Even the “inventor” of Salt Rock, Travis L. Stevens has written and said he too, has salt rock breaking up. So my advice, if you want stable rock, is to not use salt in it, or if you just have to even knowing it is bad, then use it sparingly.

Basic Procedure
Mix dry ingredients together first, excepting salt if used - add tiny amounts of water while vigorously mixing the mud. Mud should be sort of “dry” and a little bit crumbly, not wet and squishy – there is a fine line between the two. A wet mix will not have as many natural voids in it, be less porous, and will also bind to the salt, making salt release more difficult.
If you aren't adding salt, skip this next part.
Once you have reached a slightly wetter mix then you think you need, lightly toss the salt into the mixture, and then mix it very quickly – the more salt that leeches off the crystals, the more deleterious the results can be, meaning more chances for your rock to be messed up.

Be aware that a "dry mix" may give the illusion for the first week of being more brittle, but after a week or two, it toughens up and is nice and hard.
As you cast your rocks, try to "drool" the mud into place with marble sized drops. This prevents large solid masses from forming and makes lots of natural channels within the rock that will allow water to flow through the rock and seems to allow the rock to kure faster. If you are making larger pieces, you can scale your "marble" size up some, but still work at drooling the mud into place.

After you make your rocks, they need to be kept moist and warm for at least a week or two to achieve the best hydration possible – though 3-4 weeks is best. Many do take their rock out immediately and start salt release or kuring in 3 days or so, and haven’t reported any bad side effects, so it is up to you. However, new info is starting to show that to put your cement in water before the 2 or 3 weeks of age is needless, as kuring doesn’t really get going until the hydration is starting to come to a halt (there has to be calcium hydroxide for us to leech it, and C-S-H is something that forms latter in the hydration cycle). It is also starting to sound like those who put their rock into the kure bin too quickly end up with prolonged kure time, so that is something to think about too. So you can save yourself some effort and money (water cost money) by letting it sit for a while to let the chemical process in the cement have a chance at finishing doing what they are doing. Plastic bags, wet newspaper, wet casting materials and the like will help seal in moisture. If you think the rock might dry too quickly, mist it with a bottle or hose every so often.

Molding/Casting Material
Really, pretty much anything that is dry and crumbly/powdery will work. I've even used stuffing bread crumbles, but that draws bugs while it dries.

Soil
Salt
Sand
Clay

A certain portion of the molding/casting material will remain on the rocks - most of this can usually be removed with a very quick dip in a dilute acid solution, followed by a good scrubbing with a plastic or fine wire, bristle brush.

If you use a Rubbermaid type tote/bin, you can easily reuse molding material over and over again. Line cardboard boxes with plastic to prevent moisture leak and wall collapse.

DO NOT Wet Salt, if it is used as a mold material - this means when working with salt, do not add water to the casting box as you would or might with say clay or sand.

Salt gives a nice dimpled effect on the surface of the rock, but can wick out the moisture from the rock, making it dry out too quickly. You can recover and reuse any salt left over, but will notice a significant lessening of the amount of leftover salt after each casting.

Sand is my casting material of choice. You can really make some nice, layered rock with sand. Once dampened, it will continue to keep your rock moist during the hydration phase. You loose very little from the casting bin, and if you rinse your rock in a tub, you can reclaim most of what you use.


Coloring Your Cement
There is a lot of interest in creating faux coralline to make the rock more interesting while we wait for real coralline and corals to dominate. First let me say that over all, I have not had a lot of luck with using non-cement colorants. I’ve tried a gamut of stuff from RIT dye and hobby paint to Kool-aid, and none of these work. Oh, for the first couple of days, they might look great, but as the kure progresses, and as calcium carbonate forms, the colors fade out and eventually can barely be distinguished. By the time these rocks are ready for the tank, the color is mostly gone. There has been success using colorants made for cement and grout, but again, these still do fade because of what we are doing to our rock.

Having said that, I have some other things to say for those still wanting to try it. Use real cement colorants – I have a couple of sources listed below.
Sold in small amounts and in rainbow colors - are very cheap and most should be reef safe as well as mostly color fast:
http://www.earthpigments.com/produc...cfm?subCat_ID=3
http://stores.ebay.com/BEACHCRAFTER...QQfsubZ16QQtZkm
http://stores.ebay.com/Olde-World-C...4QQftidZ2QQtZkm

When you are coloring portland cement, make the color several shades darker than what you are hoping to end up with. You can choose to color the mud itself when you make the rock (as Walt Smiths' rock company does), but you will need a lot of colorant to do so, especially in grey cement. Instead, you can make up a slurry of cement and sand to make a "paint" of sorts. Use 1 part cement to 2 or 3 parts really fine sand, made fairly thin and fairly wet and sloppy (like house paint), and use it to decorate rock with “coralline algae” splotches. I’ve used white Portland, but I don’t see why white grout or mortar wouldn’t work as well – you can use grey, but grey needs a lot more colorant to reach a desired shade. You can use cement colorants to color the cement any shade you desire. Working with a paintbrush, you can easily replicate the swirling patterns of coralline. I’ve also used this mix to paint/dry brush grey Portland rocks to white.
I’ve been thinking about how the colors fade and think I might have a solution. Fast set cement. With it not really needing to kure, you could make your “paint” from the fast set, and the best part is that being impermeable, it should fade very little (fast sets carbonate very little from what I’ve read). This would be something you could add to the rock after it has been kured. Then maybe soak it for a few days after the “coralline” has cured (2-3 days for fast sets).


----------------------------------------------------------------
Now, I will list my tips and tricks, in no particular order.

Tips and tricks

1. Wear gloves when making rock. If possible, don’t let the cement get on your skin, especially the dry powder. If possible, wear a painter’s mask when measuring and mixing dry cement; this stuff can really burn the inside of your nose.
2. Setup your work area in advance; cover surfaces with plastic or old sheets if needed (like in your kitchen or living room). Fill casting containers with whatever mold material you are using, or have it standing by within easy reach. Give yourself walkways if you are making a lot of rock – nothing sucks as much as trying to create enough work space after the fact.
3. Think about the weather for not only the day you cast, but the next few days as well, if you plan on doing this outside. Rain can make a mess of things…
4. Use Portland Type I, II (I/II) or III – these are known to be safe for use and make rock with proper porosity. Fast Set cements can be used, and are in fact great for things like panels or delicate branchwork, but because of their naturally impervious nature, are not the best choice for filtration rock.
5. Mix all aggregates excepting salt into the cement before adding water. Add salt after you have reached the right wet consistency, and mix it in lightly – the less salt is leeched off the grains of salt, the stronger your final rocks will be. Water softener salt of the type “Solar Salt Crystals” works wonderfully (Thank you Travis Stevens!).
6. 1 part cement to 3-4 parts “other” is an acceptable ratio, whatever you want to mix together is up to you and you should be ok if you follow the 1:3-4 part rule - each person usually finds a recipe on their own that works best for them.
7. Work in layers for added dimension. If you lay a layer of molding stuff in your container, make a few divots in this molding layer first, and add cement to these first to make lumps on the bottom, you can avoid flat bottomed rocks. Now lay the main part of your rock, adding molding material as needed.
8. You can make neat “cliff-face” striations if you take a handful of salt, and lay it just along the top edge of wet cement, forming a narrow line of salt along the edge, laying a thin layer of cement over the salt, and repeating this to form, on the outer edge of your rock, a sort of cliff that looks to be cut by water action.
9. Anything cast thinner than an inch is likely to break, unless you are very careful with it.
10. Find a nice bit of stainless steel or aluminum wire – 2mm or so in width, and bend a handle for one end (remember you will probably be wearing gloves, so bend accordingly). As you cast your rock, use this wire to poke Lots of little tunnels all through the rock – all the way through if you can; this will make the rocks extra porous, and give bug life lots of places to hide and propagate in-tank, as well as allowing more water to move through the rock. Alternatively, you can cast the piece, and then poke as much of it as you can – though this way tends to look a bit contrived. I like the first way better.
11. Once your rock has cured and it has been curing for about a week and if you made it mixed with stuff like crushed coral or shells, mix up a weak acid mix and scrub the outside of your rocks with a stiff bristle brush. Be sure to take proper precautions when working with acid – not only from burns, but from fumes as well!!! If you only made your rock with salt and cement, ignore the acid wash, as your rocks might dissolve, but still give them a vigorous scrubbing - this will loosen the weakest stuff and get rid of it without shedding it all over your tank. If you have shells or coral, this can make the surface even more porous, and clean cement films from shells and the like that might be on the surface. I use a mixture of 1/2c muriatic acid added to 2c water.
12. You can make “lock together” pieces by wrapping a bit of PVC in something like tissue paper or plastic wrap, sticking it in the wet cement of “part a”, and then laying plastic wrap over and around the fresh cement/PVC, and then cast “part b”, making sure to get a good fit around the PVC join. I find this works, but I personally have an easier time if I cast “part a” with PVC set into it, let it cure, then wrap it well with whatever, and cast “part b”, and I can cast really large pieces this way.
13. Branching rock/Coral skeletons. Pick PVC pipe a bit thinner than what you want your final piece to be. Cut into appropriate lengths, cutting one end flat and the other at an angle. Drill plenty of holes in the PVC to help the cement stick on. Drill extra holes on the very end that will allow you to tie the pieces onto the “main branch” with zip ties. You can bend PVC into believable shapes using heat from either a propane torch or a heat gun, and a couple of pairs of pliers (use appropriate precautions). After you have your PVC framework, mix a thicker blend of Cement Paint (less water, more cement) and paint/dip the skeleton, covering completely. I recommend hanging to dry, and dipping several times, using a paintbrush to smooth it out and prevent weird drips. When done coating, tie a grocery bag around the hanging piece to preserve moisture and allow to cure 48 hours or more.
14. Think about how corals come to you, as frags and whole colonies, and think about how hard it can be to attach these in your typical rock pile. Flatter surfaces and shallow bowls in larger rock shapes can make latter placement easier.
15. You can make rock “shells” if you want to avoid the rock pile look altogether and these are only limited to your imagination and size constraints. You can stuff the cavity in the back of this hollow construction with cheap $1.99/lbs rock, or whatever you want. I DO NOT recommend making these with the cement and salt only recipe! Make a form of some sort (use your imagination), put it in a box that will fit into your tank (making a rock too big for the target tank blows), and secure it to one side, or more (for multi-part casts) with duct tape. Line the rest of the box with plastic. I made my form from plastic grocery bags stuffed into a garbage bag, with a little air added, and taped that into the target box. Slowly build the shell wall (adding details as you wish), filling the box with salt/molding material, until you have the form covered with a fairly uniform covering of cement. LEAVE ALONE FOR A WEEK! Cover with plastic if you can. See my gallery for pictures of the “”Reef Face” or “Nessy”.
16. Frag Plugs. If you have extra cement at the end of the day, make frag plugs by using a mini muffin pan, and filling with ½in. of cement. Spray the pan with cooking spray for easier release. These can be put in a mesh bag and cured in the toilet tank.
17. Hate scraping the back wall of your tank? You can make thin, wall covering sheets, that can be glued with silicone to the back wall of your tank. Alternatively you could make shelves along those lines. I find casting on a sheet of glass covered in plastic works best for this. Also marking out the actual measurements of the back wall onto the glass helps to avoid sizing issues. I DO NOT recommend using the salt and cement only recipes for this application, nor the use of any salt at all! I also mix this just a little wetter than I normally use. Once you are setup, just drool the cement onto the covered glass. I tried doing large sheets, but these mostly were too weak to hold up and heavy. I find making smaller pieces (12inX12in or so) that abut like a puzzle work best, and sort of give the illusion of looking at a cracked and crevassed reef wall. After you cast these, they need to be kept moist and unmoved for 3 days, 7 days being much better. Believe me. They do. And you will need to mist them once a day. I just covered mine with a garbage bag and used a water bottle to mist it. I recommend an acid wash, as described above, once these have kured for a week.
18. If you make a rock or rocks you don't like, either use fresh cement mix to add some new bits, or break the rock up and use it as aggregate in your next batch - no waste is good.
19. The moister you can keep the cement while it cures, the harder the final rock will be - try wrapping it in a bag, or misting it while it cures. Supposedly, if you can let it sit for two to four weeks before starting to water kure, it will dramatically speed the kure time.
20. Dust your molding sand with oat flour for easy removal of surface sand. Thanks Rhody!
21. Mix molasses with your molding sand to give it more texture. Thanks Rhody!
22. Replace up to 1/3 of your cement with “Hydrated Lime” – this reduces the over-all alumina content of the cement (and boosts the calcium content) and makes it more resistant to potential “Sulphate Attack”.

[rguyler]

Here's the second part from Insane Reefer...

Various things I have used and have worked for me for adding details:
1. Cemented Nylon String. Makes realistic tube worm/duster tubes. Make a thin paste of just cement, and dip small lengths of the sting in. Wipe excess off between fingers and lay onto the rock in desired figure.
2. Veggie Capsules. These can make little tunnels when laid end to end in the wet cement, and then covered with more cement. Or poke into outside edges to mimic polyp holes. Do NOT mix into the cement mix.
3. Nori Sheets. These can be wetted and formed into shapes or rolled into tunnels.
4. Balloons. Both the round and “animal” ones work. I find that filling them with water makes them stronger. Doubling them up works well too. Make sure that you can get the balloon out afterward - i.e. leave the knot sticking out.
5. Cardboard Rolls. Can be cut to form bracing, tunnels or for pillar shapes. Be sure to use it in such a way as will allow you to remove it after a few days of kuring. Hemostats work great for grabbing a-hold and pulling it out.
6. Tissue Paper. The white stuff you find in gift bags. Disintegrates quickly during kure. You can make little (or big) “salt bags”, that you can lay into the middle of larger rocks to give more holes for ‘pods and the like. Can be used to make caves and tunnels. Just use a small bit of paper, lay some salt in it and twist or tuck the ends – a small bit of cotton thread could be used to secure the package too.
7. Pasta. Must be cooked “Al Dente” before use. Do not mix into cement, it only makes a mess and is a pain to get out of the rock as it gets really hard and crunchy when the rock dries (ever scraped 3 day old pasta off a plate?).

Kured Rock that the pasta is stuck in...
Use to add spaces in the rock, or tunnels with spaghetti (at your own risk). Rigatoni adds a nice effect if placed just right. If you use pasta, you MUST keep the rock moist at all times – if the pasta dries, it will most likely never come out, ever.
8. Jelly. No, not like PB&J, but those toys, etc made of the product known as silicone jelly – often comes in wiggly balls. Also fishing bait worms made of the jelly/rubber. No need to lube them – they will release just fine.


Things that DO NOT work:
1. Vinegar/acid kuring. Does have its uses, but don’t expect it to kure your immature rock – it won’t. Acid, as a general rule is BAD FOR CEMENT, especially porous cement! A weak solution can be used on FULLY CURED rock to hasten the leeching of the Calcium Hydroxide, but using it too soon, or using too high of a concentration is detrimental to the cement. If you must use it, use regular vinegar at ¼ cup per gallon of kure water, and use it only if your rock is at least a month old or the equivalent (steam cured, etc.).
2. Bio-degradable packing peanuts/Cheesy-poofs. I can find no way to really use these that is also safe for the tank.
3. Fish food pellets. That was really, really nasty. I don’t want to go there.
4. Uncooked Pasta. As pasta absorbs water, it expands, causing the cement to fracture and crack – cook it al dente if you really want to use it.
5. Alka-Seltzer. Doesn’t work. It dissolves too quickly
6. Yeast. Doesn't work. pH of either the mud or the kure water kills the cells before they can respirate.
7. Co2. Adding into H2O will only make soda pop (carbonic acid), and eat away at your rock, causing fresh, high pH surfaces to be revealed. It can work, but only under high pressure, or in a dry, contained space with a saturation of Co2 for the "atmosphere".


Salt Release
If you used salt in your rock, it must be removed before kuring can happen. Salt will release in warm water much easier than it will in cold water, and really hot water (150°F) works best of all. Do not boil cement as temperatures of over 150°F can be damaging to the matrix of the rock; water boils at 212°F – 150°F is around the hottest that home water heaters go to, so the hottest tap water you have would be perfect. Also be careful about “shocking” the cement – cement is a crystalline structure and sudden changes in temperature (such as using cold water to refill a bin that was heated) can cause micro-fractures that in turn can lead to rock failure down the road. Allow warm rock to cool before putting it in cold water.

Removing the salt will take multiple water changes. It generally takes two days to two weeks to remove salt, based on factors such as temperature and movement of the water, wetness of the mud, aggregates used and density of the cast piece.

If you aren’t sure that the salt is gone, you can do a “Taste Test”. After draining and rinsing the rock (pick your largest/thickest piece), allow the water to drain out for a few minutes. Pick the rock up and use your finger to catch a drip of water from the bottom of the rock and taste it. If there is still salt present, the water drop will be salty. If the salt is gone, the drop will taste of mineral water and very slightly sweet.

Rock Kuring
Kuring your rock is the next hurdle. It is really, really best to leave your rock alone for at least a week before starting this step. According to Quikcrete reps, it takes at least 7-14 days for the rock to stop curing/hardening (though this process is actually going on for a lot, lot longer) - even though it looks and feels done. Testing standards say it takes 28 days to reach full strength and before testing for commercial applications can commence. By putting your rock in the kure bin too soon, you are wasting a lot of water, prolonging the hydration process and making weaker rock. Rocks during this 2-4 week period will naturally loose pH - from 12-13 at casting time down to 9-11, with NO WATER USED. I have been finding that by leaving the rock alone for a month or so, my average kure takes less than 2-3 weeks (and a lot less water and effort!).

Kuring is pretty straight forward. Lots of time, and lots of water changes with adequate water volume, unless you have access to a reasonably clean, free flowing waterway. This step is dramatically decreased if you wait until the 4-5 week range of your rocks life. Powerheads help force water through the rock and help the insides kure out. Adding heat to the bucket, upwards of 90°F will really speed things along, and if you can get it to around 150°F, it will happen even quicker. It is much like mixing sugar into tea. If you put sugar into iced tea, it can be almost impossible to get it to dissolve, but you can add the same amount of sugar to a cup of hot tea and it almost instantly dissolves. Same principle here. The cooler your kure water is, the longer it will take the rock to kure.

Some people have asked if there is a difference in what you kure in, SW, RO, RO Waste, Tap. For the most part, you just want to use plain tap water or rain water. RO is fine, if you have it, but doesn’t make that much of a difference. I would like to give a word of caution for those wanting to use their RO Waste Water. RO Waste Water is full of heavy metals and other things we don’t want in our tank, so why would you put something porous in that and then after it has soaked up all the bad stuff (like an oil spot on the driveway), don’t you think it will slowly release those things back into the system? You might as well fill your system with tap water. That being said, many have used RO Waste Water to kure in and claim no problems with it. But if you have a hard time kuring your rock and you are using RO Waste Water, check the pH of it before using it – if it is higher than 9 or 10, then your kure tests will never read lower then that, so at that point start using tap water.

When your bucket kured rock quits leeching out scum on the surface of the water, and stops leaving a white residue on the bottom of the bucket and on the rocks themselves, you can start checking for pH. Rock has been known to kure in as little as 2 weeks, but most bucket/bin kured rock takes 6-8 weeks to reach safe levels – some will take up to 3 months. Be prepared to wait.

When your tests indicate that the rock might be done, you will want to do a proper pH test on it. To properly test for pH, use saltwater – saltwater is preferred since this is what the rock will be sitting in for the rest of its life. Feel free to use old water from a tank change, just test the pH prior to use. Let the rock sit in this for 3-4 days without air or powerheads – you want still, stagnant water for this. After the 3-4 days, give the water a bit of a stirring and check pH with appropriate test kit. If it is in the acceptable range of 7.0 to 9.0, it is probably safe to use. If not, continue to kure.

You can use any acceptable pH testing method. The test you use should have a testing range of 5-10 at a minimum. I like using Litmus Paper. It can read pH from 1-14, and is fairly easy to read. Litmus paper can be gotten at “Hobby Lobby” for $3.89 per 100 strips. These can also be used to test your reefs’ pH Litmus can also be found at pharmacies, online, and at other full service hobby stores, usually in the section that has things like “Magic Crystals”, and horseshoe/bar magnets – the “Science Section”.

Once kuring has finished your rock can be used

If added to a newly established tank, you can go ahead and put it all in at once. If the tank is older, with inhabitants, you may wish to add a rock or two at a time, to allow the system to “settle” between each addition. Maintain pH testing for the first two weeks and buffer if needed.

Expect an algae bloom.
A few people, those who either have waterways to kure in, or those with really butch systems have reported no algae blooms, but I suspect they are the exception, not the rule. If your tank blooms, don’t panic. Most tanks bloom within the maturation period anyway. Double check your system for things like NO2 and NO3, and other algae causing symptoms and correct anything that isn’t up to snuff. Take all the normal steps to curtail the growth, but then just ride it out. If the bloom is caused by the rocks, the algae will soon deplete the readily available nutrients and starve itself out. If it doesn’t go away within a few months, then you should check into other reasons for the bloom.

If you place your rock in tank with low light for two weeks to a month, you can avoid most of the bright green covering algae – low lights allow the rock to settle in without being attacked by algae so badly, or so it seems, IME…

Expectations
And in conclusion, I'd like to address expectations. I have a feeling that some people are expecting the rocks they make to be as hard as cement blocks or cement stepping stone, because, after all, they are made with cement, so it should be, right? Well, in this case, no - they won't be.

Let's compare our “mud” to a typical cement poured “slurry”.

First, poured commercial slurry's are made with a higher ratio of cement than we usually use. Next, they add enough water that they can pour the slurry - much like a milkshake. I've never been able to pour my mud; we try to make ours as dry as we can and still have it stick together. Now take a look at the aggregates - they use dense sands and gravel, we usually use calcium based substances when we can - there is a marked difference in each of these as far as strength goes.
And finally, when cement is poured, they try to get it settled down - they drag tools over it to smooth it and make sure it is even and all that, and sealing the surface. We go for as much openness as possible, and we try not to pack the mud if we can help it.

Looking at it like this might help people come to a better understanding of what a reasonable expectation of their rock might be.
Our rock is going to flake and shed. The more porous the rock is, the more likely it will be to do so. The better the mud is made though, the less you will see of it. Maybe you have seen a box of real live rock just after shipping. If you have, you probably noticed the rubble in the bottom. Most distributors are not in the habit of making up the extra weight in a box with rubble - that would be bad business. Most of that rubble simply came from the rock during shipping. Calcium based rock is not the strongest in the world, and essentially, our rock is calcium based.

But flaking and shedding are not the same as brittle rock. Your rock is brittle if you can snap large pieces off after a month or two. Small bits rubbing off is not necessarily indicative of failed rock, those could just be pieces that didn't get adhered well.

My first piece of advice would be to wait. It takes a month for the curing process to reach near completion and the rock to reach something close to its final strength. If your rock seems brittle or flaky, beyond what you should reasonably expect, just leave it alone for a month, in a moist (not wet), warm environment, like a plastic bag. Some of the early salt rock I made seemed really brittle, too brittle to use, certainly, for the first couple of weeks. It was when I later found it again, in the bottom of a bucket outside, that I realized how nicely it had hardened up. If after leaving it alone, you can easily snap sizable portions off (golf ball sized?), then you have a problem.

My next piece of advice would be to use a stiff bristled brush, like what you use to clean your grill, to give your rock a good once over when it reaches about four weeks old (or after the pH test in Jiffy Rock). This will remove about 90% of the shedding and flaking, if the shedding and flaking isn't due to rock failure that is. If you have done this and a couple of weeks later it is readily shedding again, then I'd say you might have a problem.

Remember that even slight variations can make a huge difference. Humidity and Temperature at casting and during the cure can make drastic differences. A tablespoon of water can make a difference on smaller batches - too wet and too dry can be a fine line. Differences in the cement itself can wildly vary - every plant uses its own recipe to make the clinker. Differences in local materials used for the recipe can often vary with availability and cost. My white cement is going to be different then Neptunes' cement, and his, even from the same plant as Sunkools' may vary as well, from lot to lot.

Salt can mess up the strength of your rock, so if you used salt, think about that. If you added it upfront, with the aggregates, you may have over-mixed it and too much salt mixed into the batch. Try adding the salt after the mud is mixed and ready - and just lightly mix it in.
A ratio of 1:3 to 1:5 is best for us. 1 part cement to 3-5 parts "other", which can include salt.

And finally, realize that even the best made rock can still chip and shed once in a while. Moving it around in your tank, bumping it against each other (esp larger pieces), will inevitably cause bits to shed or chip off, unless you went for rounded ball like shapes, which seem to loose less, but also seem less porous and less attractive too.

I hope this helps a few people out there. I know that having something you worked hard on, that doesn't turn out like you wanted, can be disappointing. Hopefully this will help people understand what they should expect, and what they can do to correct it...

Well, I think that about covers my repertoire. I apologize for the length of this post, but hopefully some of you will find something of use…

[SpankythePyro]

Yea rguyler I have all that bookmarked.

I want to know if I should wash my crushed oyster shells though, it looks like it would remove a majority of the product though as it is dust

[big400g]

SpankythePyro, it is called medium sand by Quickcrete.

rguyler, wow that is a lot of info I will have to read

[SpankythePyro]

Around me is Quikcrete All-Purpose, Play Sand, and Sand/Topping Mix

[rguyler]

Spanky, that wasn't really directed to you, just passing on general info.

I would wash everything I'm planning to use. I've read comments from others who said their oyster shell had a good amount of other stuff in it. I also think that something that fine won't help much with reducing the density of the concrete, which was the original reason for such additives.

[big400g]

After reading the long info you posted (thanks for that) I am glad to see the use of hydrated lime is acceptable. I love what it does to my cement mixture 1 cement, 1/2 lime, 1 sand/crushed coral etc would be good, use things to poke holes in the rock, forget about the salt.

[SpankythePyro]

rguy, yea but it is the same size/shape as crushed coral.

I found perlite today but couldn't determien if it had fertilizer in it or not.

[mr.wilson]

I have made quite a bit of faux coral rock with crushed oyster shell as the aggregate. I have recently gone back to using coarse aragonite, as the oyster shell has a high dissolution rate that affects the strength of the concrete. There have also been some comments about impurities (heavy metals) in the oyster shell.

We discussed silica sand at length earlier in the thread. I got run off the thread the last time I voiced my opinion and experience on the matter

[Insane Reefer]

Originally posted by mr.wilson
I got run off the thread the last time I voiced my opinion and experience on the matter

Would have been fine if you had kept it to opinion, not tried to pass it off as fact, especially since you were offered opportunities to back your claims, but you never bothered to offer any sort of proof...

And you weren't run off (how would that even be possible, come on, be real) - you got ****y and left.