I've built numerous zoo exhibits and for rockwork used a mixture of portland cement, sand, concrete dies, and an expensive acrylic additive. The mixture was shaped onto stainless lath and then molds were pressed into and removed from the curing mixture to provide naturalistic texture. The molds, which I cast from real rocks, bark, etc., were made from an expensive two-part rubber compound.



I'm sure there is some decent replacement for the acrylic additive but I've not bothered to look. The concrete rockwork also requires a sealer which can be expensive unless you don't mind a shiny, plastic look to the rockwork.



So even if suitable replacements were found for the above products, one would still be left with a very heavy background.



I wrote all of the above so you'll consider plaster instead of concrete. I have much less experience with plaster but the site I linked below looks like a promising method. Be sure to navigate around the site and look at all the cage construction pages.



Styrofoam sheeting could be used in place of the strips of wood he used.



Instead of the rubber molds I used you could spray real rocks and bark with cooking spray or oil and press them into the drying plaster. The plaster will not allow for as deep of texture as the concrete but should still be workable.




plaster/epoxy rockwork

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