The majority of hand-sculpted artificial rock is created by pneumatically applying concrete to a rebar frame, then hand texturing it. Some companies initially shoot a structure coat, then cover it with a texture coat for the sculpting and details. The product is often hollow and shot over a forming material such as metal lath. Carvers sculpt the stone into the correct shape, then create crevices and texture to provide the appearance of individual rocks.
This method is more economical than utilizing glass fiber reinforced concrete castings, particularly on larger projects. It also affords more diversity, since each sculpture can be carved to replicate any variety of rock.
However, the hand sculpting method is generally more time-consuming and relies heavily on an artisan’s skill level, since all the work is completed by hand.
From a visual perspective, the success of this method is entirely dependent on the creation of realistic detail, beginning with the armature. The frame should be as detailed as possible, and while some professionals choose to outline a rough impression and leave it to sculptors to carve the shape, this is not recommended.
If the shapes are designed well, then the carving will enhance them, and the paint, in turn, enhances the carving. Conversely, a poorly delineated shape means a carver is tasked with repairing the shortcomings with his or her rendering, and it will never quite hit the mark.
Even major cracks should be formed in the armature stage. Bend the rebar to depict large fissures, and exaggerate them so they remain visible when the shotcrete or gunite is shot. For example, a 3-inch crack running diagonally across the face, might require a steel gap of 7 to 10 inches wide.
Creating the correct angularity can prove challenging. Rounder forms are generally simpler to design when hand carving because of the concrete’s natural slump. However, it’s important to take the time to create proper angles. To make this easier, some professionals enhance the concrete mix with 2 pounds of structural fiber per yard so that it doesn’t sag as much. The fiber creates a more substantial form that can be modeled similarly to clay.
This method also requires impeccable timing. After the concrete is sprayed, carvers have limited time to work with the material before it sets. To combat this, some tasks should be completed while the material is fresh and others delayed until after it sets up a bit. To that end, start by forming the basic shape and then quickly segue to delicate cracks and fissures.
After the material is less pliant, carve larger cracks. This leaves a rougher, more jagged feel. Otherwise, it may appear that the cracks were cut cleanly as if through butter. It’s a good idea to use harder, denser tools such as trowels or knives, to cut in the bigger lines. As the surface becomes harder carvers can pick at it with trowels.
Hand sculptors must also know how to approach the pebbly texture left behind by the shotcrete spraying process. Some professionals do whatever is possible to eliminate it, while others incorporate it into the design. These sculptors utilize the natural randomness to the spray.