How to Sculpt With Concrete

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Who says concrete can only be used for construction? With the right techniques and application, concrete can be a wonderful sculpting medium.

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Steps

1. Note that most concrete work is done using a form or mold. If the sculpture you want to create is orthogonal in shape you will want to make a form out of plywood and 2x4's in order to contain the concrete until it is set. When the concrete is set you can remove the form and your sculpture, or part of it will be cast in the shape of the inside of the mold you have created.
2. Be aware that if you want to create a sculpture of a more organic nature using concrete, your task will require a different technique . you will need to build a steel framework using steel, rebar, and "pencil" rod (up to 1/4 steel rod) welded together in the basic shape of your sculpture. You will also need to add fiberglass to your concrete mixture, and the mixture will be a little drier than for pouring as you will be applying it to your framework by hand.
3. Purchase the cement and the aggregate, or the sand, pebbles and small rocks that turn cement into concrete. The instructions for how much of each of these to add to the bag of cement is on the bag. Aggregate will not be needed if you are sculpting by hand
4. Continue to build the formwork for the shape you wish to cast. Keep in mind that the concrete will harden into a mass of solid rock like stuff once it is set. You will have to design the mold to be able to be removed from the form. Think ahead. The mold can be constructed out of plywood, the larger the mold, the thicker the plywood, and held together on the outside of the mold with 2 x 4 lumber. Again the larger the mold, the larger the lumber (2x6, 2x8 etc...). You might want to check some books on residential construction to see how concrete forms are constructed for some tips on building formwork.
5. Coat the inside of the form. Do this with wax, or silicone or some other material that allows for easy release of the mold after the concrete is set.
6. Understand that if the concrete is very large you should think about adding some steel reinforcing to the center of the mold, ie, rebar. This should not be strictly necessary if the sculpture is not more than a few cubic feet of concrete. Remember, concrete is very strong in compression and weak in tension, steel is strong in tension. So if your sculpture is going to have any tensile strength you will need to add some rebar to the inside of the concrete. keep the rebar 3inches away from the surface of the concrete on all sides.
7. Mix and pour the concrete into the mold. Take care when filling the mold to avoid any air pockets forming in the concrete. You can vibrate the concrete or push it around with a poky thing of some kind while you are filling the mold.
8. Wait at least 48 hours to unmold the concrete. keep the concrete damp while it is curing. The concrete will cure for a month but you only need to keep it damp for a week or so. You can cover the sculpture in plastic to ensure it stays damp while it cures.

Tips

• You can buy concrete colorants and stains to turn ordinary grey concrete different colors.
• Check out books on construction for tips on how to build formwork.
• Check out the various organizations that work with cement and concrete for more information on working with this material.
• For concrete sculpting inspiration check out: **http://www.imaginationcorporation.ca/ **http://www.signcraft.com/pdfs/97-127002.pdf

Warnings

• Concrete can burn your skin and eyes and lungs, wear gloves, protective clothing and protective eye-wear and a dust mask.
• If you get the concrete on your skin wash it off right away.
• Do not breath concrete dust as you mix the concrete - wear a dust mask.

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Sources and Citations

• http://www.howtomixconcrete.com - source information provided in part
• http://www.gardenstatues.ca - source information and pictures provided in part

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