Q: How do you go about making concrete sculpture like the kind you can buy
for your garden?

A: Generally, this type of sculpture is done by making a full-sized model
in clay, usually plasticine, then taking a mold from the model and pouring
in the concrete mix. Reinforcing metal rods can be used or not, depending
on the configuration. Though this used to be done with plaster piece-molds,
now flexible urethane rubber molds are generally used, with a rigid shell,
either in plaster or fiberglass, to hold its shape. A mold release will increase
the life of the mold and facilitate removing the piece without losing fine
surface details. A concrete vibrator is helpful for removing air-bubbles before
they set, and for compacting the mix. Various admixes can be used, including
super-plasticizers to reduce the water and increse the final strength of the
concrete, as well as combat water separation and weeping. Air-entrainment
agents will help the sculpture resist freeze-thaw cycles outdoors. Wait 2 days
before unmolding, and wet-cure the concrete cast for at least a week.

Andrew Werby - United Artworks


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