Hand-carved rockwork

Concrete Construction, June, 2003 by Joe Nasvik

There are many ways to build artificial rockwork, but the first method probably involved hand-carving shapes in concrete or cement plaster placed on a three-dimensional rebar-and-lath frame. This process is referred to as "positive rock" or "hand-carved" rockwork, and the finished product is almost entirely dependent on the skills of those who carve and texture the rock shapes. The resulting look can suggest the look of rock--or it can be so realistic that the viewer wonders how the owner was lucky enough to have a natural rock outcrop located on the site.

The Walt Disney Company is probably the largest specifier and constructor of artificial rockwork in the United States. Walt Disney Imagineering (WDI) designs, project manages, and sometimes self performs rockwork projects that require the most demanding detail. WDI manages its projects using field art directors and production designers--not the typical personnel usually associated with construction sites.

Designing the Disney way

Disney's mission is to entertain, and it does so by telling stories. Exhibits and theme areas become a three-dimensional backdrop for immersing the guest into a story. According to Gary Graham, a senior production designer at WDI in Florida, "Rockwork is a three-dimensional part of storytelling. It's always set in context with a story." Cicero Greathouse, also a senior production designer, adds, "When you enter a Disney park, you will sometimes see rockwork on the way in because it helps you start thinking about the story."

Designing rockwork is an involved process. It starts with detailed drawings. Based on the drawings, a "massing model" is carved out of foam to represent the aesthetic and volume of the project. Next, a scale model is constructed (sometimes the massing model can be used for this purpose). Contractors use the model for doing "takeoffs."

Sometimes Disney projects, such as Disney's Animal Kingdom, represent different parts of the world. Very detailed location photos showing indigenous rock are used to quantify the scope of work. River banks and eroded strata formations are identified as reference points on the plans to show the type of rock and the formation required.

When rockwork is located in areas close to the public, Disney artists often build full-scale mockups or "referee samples" that help bidders understand the level of detail expected and assure Imagineers that they will get the result they want.

Types of hand-carved rock

Graham refers to wall features and facades made with cement plaster as "character facades." Artificial rockwork is defined as three-dimensional and free standing. The two methods most frequently used for rockwork shapes are the "lath-and-plaster" technique and the shotcrete process.

The lath-and-plaster technique involves constructing a frame with rebar and attaching diamond metal lath (the same lath used for plastering walls) with tie wire to the frame. The reinforcement is easy to install and bend into position because the rebar is often #3 bar and pencil rod.

Workers next apply a "brown coat" or "scratch coat" to the frame with trowels. When the brown coat is hard, they apply a "theme coat." Graham adds that this is often spray applied. More than one application of theme coat can be applied in order to build the three-dimensional shapes needed for the final appearance.

When an engineered structure is needed, as, for example, the control walls for animals in Disney's Animal Kingdom, shotcrete is the preferred method. This process starts with engineered three-dimensional concrete walls joined to footings with rebar. When the reinforcement is placed, workers attach a special clip to the reinforcing bars, to secure a polyester weave "back-up" fabric to the frame. This creates a back form surface for the shotcrete and ensures that concrete can be sprayed around the reinforcement, positioning it towards the center of the placement. Graham adds that Imagineering usually requires 2 to 4 inches of structural cover over the reinforcement. This is an advantage of using shotcrete over the lath-and-plaster technique--the reinforcing bars are encapsulated in concrete, minimizing corrosion, a significant problem for artificial rockwork, especially when water features are included.

Constructing the reinforcement

Reinforcement is important not only for structural reasons, but also for providing the three-dimensional character of rockwork. "The time-honored method is to do all bending in place, in the field," says Greathouse. "Usually rodbusters bend the bars to approximate what the designer had in mind. But sometimes rock structures are intricate and must exactly replicate the model. So, taking a lesson from the bridge construction industry, designers use computer-assisted drawings (CAD) to produce digital surveys of steel reinforcement locations and bends. Companies that specialize in bending reinforcement bars can then automatically cut and bend for each location on the survey--making the finished work exactly match the plan." When reinforcement is pre-bent in this manner, each bar is tagged to identify its location and then assembled either on location or pre-assembled into manageable units, hauled to the location, and positioned.