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When you visit the North Carolina Zoo, you will see rocks.
They’re one of the park’s most dominant features, especially when used as confinement walls within animal exhibit areas.
They look real and as though they’ve always been there. But most of the rocks within the exhibits are man-made – a complex creation of wire mesh, steel armature, concrete and skilled sculpting.
Although these artificial rocks might all look alike at first glance, a closer look will reveal a variety of shapes, color variations and details. In addition to adding an aesthetic element to the exhibit, they also serve two other important functions: as barriers and as concealment.
Artificial rocks play an important part in containing the animals.
Some of the zoo’s animals are excellent climbers and jumpers, so rocks have to be designed not only to look natural, but also to keep the animals in their habitats. Besides their use as exhibit retaining walls, these man-made rocks also serve as means to hide elements such as barns, feeder bowls, doors, fences and moats from the visitors’ line of sight.
Artificial rocks (along with man-made logs, stumps and trees) also serve as natural architectural elements, supplying overhangs instead of roofs and viewing ledges instead of decks.
The zoo’s Design Department staff members – who actually construct the artificial rocks – study actual rocks, photographs, clay models, and their own sketches and drawings to ensure that their artificial rocks are as true to natural formations as possible – even down to the lichens, mosses, cracks and weathering process.
“Two factors basically decide the look of the rocks that we make,” said Philip Link, a member of the design team who constructs the rocks. “First, the type of natural rock that would figure into the exhibit’s locale will determine the appearance of our rockwork. Secondly, we use resource material such as photographs and rock samples from the area to obtain the look we are after.”
The rocks must not only appear real, but also must fit the overall habitat design. One of the first steps, articulation, begins with a frame structure, mostly constructed from steel rod.
This structure defines the rock’s contour and form and supports the concrete covering. A metal mesh, or lath, is then attached to the framing to hold the concrete.
Concrete is usually applied by high-pressure hoses that blow the concrete onto the form.
This initial concrete covering averages about four inches thick, depending on what animal is being contained. Not surprisingly, lizards require less and polar bears, considerably more.
The surface must then be finished by hand. Using masonry trowels and brushes, design artists either brush the concrete for a smooth finish or “carve” it to simulate cracks and folds.
For detail work, the concrete must be applied, at times, by hand. For Link, this hand carving of cracks and fissures is the hardest part of the construction.
Painting, the final step, is done with a special mix of concrete, dry pigments and a liquid binder.
Large areas are sprayed with several basic colors or splattered with paint thrown from a distance. Different lichen shapes can be achieved this way.
Splattering can also be done by flicking paint by hand. Large lichen patches and details are also painted by hand.
But in the end, the final measure of success is how well the builders mimic the rocks common to the zoo’s geographical location.
“Ideally, it must not call attention to itself but rather express the natural unity of the whole,” Link said.
In the end, these man-made rocks – along with artificial logs, trees and stumps – must be not only functional, but also must be aesthetic elements that add to the visual effectiveness of the exhibits and to the visitor’s enjoyment.
Tom Gillespie lives in Trinity and is a journalist and public affairs specialist at the North Carolina Zoo. For more information on the zoo’s plant and animal collections, special events and education programs, go to their Web site at www.nczoo.org
