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Concrete

Art Concrete: How-to Guidelines + Use

Home | HOW-TO | Materials | Small Scale | Mesh | Casting | Colour | Hazards | Books | Sources |

THIS SERIES OF PAGES offers some detailed guidelines and recipes from my own experiments and research into using portland cement concrete for small scale art projects (jewellery, sculpture) along with ideas contributed by other artists. The series covers everything from materials and techniques to sources and hazards.

Book: Concrete Handbook for Artists: Technical Notes for Small-scale Objects. More information?

OTHER PAGES in this web site deal with more general technical questions, and you may want to start there. There is also a basic FAQ page, and an extensive list of art concrete links.

Also, here's a two-page PDF file of some workshop notes.


BRIEFLY...
Uncured concrete is difficult to handle directly. It usually needs some kind of form or structure to control the shape. This leads to three completely different fabrication methods:

  • casting into a form -- and later removing the form
  • applying to an armature -- expanded mesh, for example
  • or carving a solid block -- which can be partially cured
Concrete is a mix of portland cement, an aggregate, water and other additives that give the mix certain characteristics. Aggregates vary depending on scale, colour, strength:
  • large: stone or gravel
  • small: sand
  • fine: stone dust (eg limestone or marble)
  • extremely fine: silica fume, metakaolin
All measurements are given as volumes, or relationships of volume. The dry materials are mixed first. Water is added to the dry mix. Do not add too much water; the drier the mix, the stronger the final product. (Excess water stays trapped in the cured cement.) How wet to make the mix is a function of the process: casting in a mold will need a wetter mix that slumps into place. Applying the mix to a wire mesh will need a drier mix that feels more like clay and stays in place until it sets.

Concrete will get somewhat hard after 4 to 12 hours, depending on the mix and temperature, and can be worked with coarse files or carved at this stage. In one or two days it becomes harder still, but it is possible to wet sand to refine the shape. After that it becomes comparable to working with stone. It is best to add layers of new concrete within the first day or two after the initial set, when almost complete bonding takes place, but it is possible to add layers for several days.


A reader to this site sent me an Excel spreadsheet that simplifies volume calculation. You can download it here. Enter length, width and height in inches for a cubic volume, or height and radius for a cylindical volume in cubic inches or feet. [Thanks to Lynn Aavang.]


I welcome your input!

~Andrew Goss

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Last update: May 2008.


 
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