help on casting concrete for outdoor sculpture 6

[pottermanks]

I am an artist who wants to expand into creating outdoor cast concrete sculpture. My first question would be what type of cement would be best for casting, what type of aggragate or reinforcement should I use and if using bonding agents would help in longevity and strength. Another question that has me perplexed since I am a creative person and not a mathematical computator is how do I figure the amount of material needed to cast an object that is abnormal in shape? Any help you can provide with these and any other problems that I might run into would be greatly appreciated. P.S. This is a wonderful site!

 

[JAE]

Typical Portland cement Type I will give you a grayish color. There are brands of white Portland cement that can provide a lighter shade. Two sizes of aggregates are used in a typical concrete mix. Course aggregate varies in size from 3/8" to 1 1/2". Fine aggregate is typically sand.

For a sculpture, the smaller aggregate would perhaps be preferable to allow better distribution in tight corners.

If the sculpture is intended to be outdoors, and you live in an area with freeze-thaw potential, use air entrainment admixtures.

Reinforcing - depends upon the size, nature, shape of the sculpture. More solid objects, such as a cube, might not need anything. A piece that involves legs, thin extensions, etc. could probably use a single bar (#3 or #4 - 3/8" dia. / 1/2" dia) down the center.

Bonding agents - I don't think - would help. You could consider a fine fiber reinforcing such as Stealth, by Fibermesh, Inc. This would hold the piece together and the smaller size of this particular product would avoid getting "hairy" concrete.

Quantity of concrete and concrete mix design: Ask your local ready mix suppliers for advice on the kinds of aggregate and cement available in your area. They can also provide you with some of their standard mix designs as well. Keep in mind the aggregate, primarily the fines, do affect the color of the final concrete material.

 

[Qshake]

One more thing to add JAE, there are also a number of color admixture products out on the market too. This might be helpful in achieving a consistent color in various batches.

 

[dik]

Try to get some information on ferrocement. The sculpture frame can be put together with small rebar welded together. Over this framework, a layer of fine mesh (approx 3/8" squares) is wired to it and the stiff concrete mix is 'trowelled to this'. The mix used can be a fine sand mix. A thin layer is first trowelled on, and then strips of mesh; very much like paper mache.

This method was used for constructing concrete boat hulls.

Colouration can be done using pigments as noted above; I used white medusa cement for the coffee table I built. Also want to make sure that the sand aggregate is clear. It will impart a colour also.

If outside exposure, then use a sealer to protect the concrete. Make sure that the sealer has no adverse 'long term' colour effects. Talk to one of the building material suppliers about one that doesn't age or discolour in sunlight.

 

[phuduhudu]

I noticed one part of your question that wasn't answered about the quantity of concrete needed for your sculptures. If you have a mould it should be easy. Pour sand or polystyrene packing balls or anything like that into the mould until it is full then pour it out into a bucket or drum of known volume and that should tell you how many litres of concrete you need. From the mix design you can then get the quantity of stone, sand, cement and water to achieve that yield of concrete. Carl Bauer

http://www.bauerconsultbotswana.com

 

[spammail1000]

Something I found this weekend were some articles on "Hypertufa" concrete garden ornaments and containers using a mix of Portland cement, Peat moss, perlite, fiberglass fibers and concrete dye.

Two different articles had the same recipe. One from "Black and Decker Outdoor Home - Building Gardent Ornaments" by Creative Publishing International Minnetonka, Minnesota, and another by "Horticulture" August 2001 Pg 28 - 31.

The articles speak to some significant cure times, then a significant dry time, then a propane flaming process to remove the fuzzy fiberglass extensions from the concrete.

 

[dik]

Just a caution... the alkali in concrete can dissolve glass fibres... they have to be coated with a protective surface...