DIY Cement Live Rock

Recipe for making cement based reef rocks.

If you plan on making your own rocks. If you have not already done so, I recommend you read GARF's Aragocrete web site info. They even have a mpeg movie showing an arch rock being made. What is most important is that any rock is cured properly before adding it to the aquarium. The following is the recipe I used and a brief description of the process. The rocks I created were so porous that water just runs right through it. Pictures of my first batch of rock sculptures to be used as base or live rock in my 120 gallon aquarium.

Ingredients

Rock:
  1 part Portland Cement (Regular Type I/II can be used but I used white type II).

  4 parts crushed oyster shell (Chicken feed supplement purchased at AGWAY).
     For some rocks I substituted 1 part crushed coral and used 3 part oyster shell.
     You could also use 5 parts oyster shell and omit the sand.
  1 part aragonite sand.

Exterior accents and decoration:
  Crushed coral, Large Puka shell substrate, additional dry oyster shell.

Mold:
  Plastic Storage Container
  Aragonite Southdown - Oldcastle Tropical Play Sand

Rubber Gloves:
  Wear rubber gloves at all times working with cement.
  It is very caustic and can cause irritation and burns.

Mix dry rock ingredients (shell, coral, sand, and cement) in a 5 gallon bucket first before adding any water. I used one bucket for mixing dry and another for adding water and dry mix together. This way a larger dry mixture could be prepared ahead of time. I would then mix only enough dry ingredients in a separate bucket with water that was needed for the rock I had planned to create at that time. Be sure to not add too much water when mixing.

Half fill the plastic storage container with aragonite sand for the mold. Dampen the sand (Make sure not wet only enough to form mold) and form a mold for the rock you want. Sprinkle Crushed coral, Puka shells, dry oyster or other shells in mold to add decoration to outside of your rock.

Mix enough of the dry ingredients with a small amount of water. Be careful how much water you add. Mixture should not be runny but dry enough to hold together like a good mud ball and not drip.

Add small portions of mix to mold. Do not form just drop into mold. This will keep it porous and cause irregular natural shapes.

Cover the mix with more decorative shells then cover with additional dry aragonite sand.

Let dry for at least 24 hours. remove from mold gently and then rinse off lose sand.

Cure your rocks in tap water before adding to aquarium.

It is critically important that live rock is properly cured or be prepared for big problems and death. The cement in your  new live rock can raise the PH in and aquarium to dangerous levels. Cure rock for at least 6-8 weeks or more until the measured PH has stabilized.

The most important step after creating your rock is preparing it for use by curing. This is different than curing natural live rock. With natural live rock the curing process takes place in seawater. When die off on natural live rock has ended and ammonia and nitrate have stabilized natural live rock is cured. When curing your home made live rock PH is the measurement that needs to stabilize.

To cure your new rock fill a container with tap water and completely submerge rock to soak. Change the water in your container at least twice a week. Use a PH test kit to verify that rocks are cured before adding to aquarium. After 5 weeks completely drain any water in container the rocks are curing in. measure the PH of your tap water and record it.  Fill the container back up and let the rocks sit in still stagnant water for one week. At the end of the week measure the PH of the water in your live rock container. If PH has risen at all repeat this process each week until ph readings are the same.

Log of Water Parameters during Curing