How to make live rock?

Salty Brother

New member
I remeber coming along a thread a while back where a bunch of people succesfully made LR. I remember they did it with like a certain kind of cement and oyster shells. So I was wondering if someone could help me out by either telling me how to make my own LR, and like the time it needs to cure. Or if someone could just find me that thread.

Travis L. Stevens

New member
There are many ways of making DIY Rock. There is no right or wrong way, but it does depend on what you're trying to achieve with your rock. The main thing about the rock is the Portland Cement. This is the boon and bane of the DIY Rock Maker. It is what makes the rock, and it's also what causes the increased pH that many diligent people are attempting to find ways of decreasing immediately, or at least shortening the time it takes to take it out of the rock. Insane Reefer has pioneered many techniques, thoughts, and new ingredients that is paving the way for reduced Kure times, the time it takes to release the Calcium Hydroxide from the cement that spikes the pH. Her latest update is as follows:

<a href=showthread.php?s=&postid=10393469#post10393469 target=_blank>Originally posted</a> by Insane Reefer

Hey All,
I'm going to post my favorite tips and links every so often 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. Lately, I have even made some money on my rocks.

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 traditionally cured rock methods.

I thought I’d pass this info on â€"œ maybe save someone some frustration or spark a new idea.

I will continue to refine and update this post as more info is added, and repost every so often.

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.
Reef Propagation Project:

And this link is for Cement Colorant . They sell it in small amounts in rainbow colors and are very cheap.

List of Appropriate Aggregates
Sand - caribbean/aragonite is best, but very hard to find at a reasonable price. Any “clean” sand will work. “Toys R Us” carries a play sand that a lot of folks use and report no trouble with. 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 Home Despot. Sand Blasting sand can also be used and is sugar fine.
Crushed Coral - AKA "CC". Makes nice, realistic rock, but expensive.
Crushed Oyster Shell - AKA "OS". Any shell will work, but OS is very cheap at feed stores.
Calcium Carbonate - This stuff comes in a range of textures and grain size â€"œ from sand to gravel like CC. Most feed stores will carry it, and for less then $4/ #50.
Dolomite :D â€"œ Same as Calcium Carbonate, just another name (and slight chemical variation) and is just fine to use.
Perlite - Completely inert and cheap. Use to replace CC in Ol' Skool mixes.
Salt - Many thanks to Travis 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 Recipe: 4:1 or 3:1 / Salt:Cement
Improved? Recipe: 3:1 or 2:1 / Salt:Cement
Ol' Skool+ Recipe: 1: 1 to 1.5 : 1.5 :1 / Salt:Cement:CC&OS(mixed):Sand

Mix dry ingredients together first, excepting salt - add tiny amounts of water while vigorously mixing the slurry. Slurry should be “dry” and crumbly, not wet and squishy â€"œ 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. 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 â€"œ the more salt that leeches off the crystals, the more deleterious the results can be. Be aware that a dry mix may give the illusion for the first week of being more brittle, but after a week or so, it toughens up and is nice and hard. After you make your rocks, they need to be kept moist and warm for a week or two to achieve the best hydration possible â€"œ though many do take their rock out and start salt release or kuing in 3 days or so, and haven’t reported any bad side effects. Plastic bags, wet newpaper, 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 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.


A certain portion of the molding material will remain on the rocks - this can usually be removed with a short acid bath, followed by a good scrubbing with a plastic or fine wire, bristle brush.

If you use Rubbermaid or Tupperware, you can 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.

Now, I will list my tips and tricks, in no particular order. Many will seem stupid or like common sense, but you don’t know about some people’s kids, lol…

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 â€"œ 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 â€"œ these are known to be safe for use and make rock with proper porosity.
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 â€"œ 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. I prefer to use crushed coral and sand in my rocks for long term strength, plus salt to add porosity. The aggregates also give realistic details to the rock. My preferred recipe is 1.5 part cement + 1.5 part sand + 1 part crushed coral/shell mix + 1 part salt, but this is expensive to make. You can also use a mix of 1-1.5 cement + 1-2 crushed oyster shells + 1-2 salt.
Mainly, a 1 part cement to 3-4 parts “other” is acceptable, whatever you want to mix together is up to you and you should be ok if you follow the 1:3-4 part rule.
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 â€"œ 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 â€"œ 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 â€"œ 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 â€"œ 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. “Cement Paint”. You can make up a slurry of cement and sand, say 1 part cement to 2 or 3 parts sand, made fairly thin and fairly wet and sloppy, and use it to decorate rock with “coralline algae”. I use white Portland, but I don’t see why white grout or mortar wouldn’t work as well. 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.
14. 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.
15. 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.
16. 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”.
17. 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.
18. 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.
19. 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.
20. 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.
21. Dust your molding sand with oat flour for easy removal of surface sand. Thanks Rhody!
22. Mix molasses with your molding sand to give it more texture. Thanks Rhody!

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 â€"œ 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 â€"œ 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 â€"œ often comes in wiggly balls. Also fishing bait worms made of the jelly/rubber. No need to lube them â€"œ 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 rock â€"œ it won’t.
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 â€"œ 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 kills the cells before they can respirate. Though during the Kure, this might be a speed option.
7. Co2. Ok â€"œ it does work, but only under high pressure. Adding into H2O will only make soda pop (carbonic acid), and eat away at your rock, causing fresh, high pH surfaces to be revealed.

Salt Release
If you used salt in your rock, it must be removed before kuring can happen. Salt will release in hot water much easier than it will in cold water, and boiling water works best of all. It generally takes two days to two weeks to remove salt, based on factors such as wetness of the slurry, aggregates used and density of the cast piece. Removing the salt will take several water changes. Boiling is also a viable option, and may also help reduce pH - hydrogen carbonate ions can decompose forming insoluble calcium (or magnesium) carbonate, which then are flushed away.

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 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 9-10, with NO WATER USED. I theorize that rock left longer, like 8 weeks, will only need a week or so of kure time (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 waterway. Powerheads help force water through the rock and help the insides kure out. Adding heat to the bucket, upwards of 90°F will speed things along.

When your bucket kured rock quits leeching out white 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 â€"œ some will take up to 3 months. Be prepared to wait.

To properly test for pH, change the water â€"œ either use RO/DI or aged saltwater â€"œ saltwater is preferred since this is what the rock will be sitting in for the rest of its life. Let the rock sit in this for 3-4 days without air or powerheads â€"œ 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 8.0 to 8.6, 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 â€"œ the “Science Section”.

Once kuring has finished - reads between 7 and 8.6 on pH, 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. :eek1:
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.
New Tip! 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 â€"œ low lights allow the rock to settle in without being attacked by algae so badly…

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…

I encourage the rest of you to take some time to write up your experiences and tips and share them with us â€"œ by sharing our experiences, we all learn and get better and better at making our own rock.

Good Luck, and Rock On!


Premium Member
I just added two small pieces of DIY rock to my tank. Let's see...It is the end of July and I made it near the end of APRIL!

I got some cool shapes, and have about 50 more pounds in the "cure" process.

Good luck!