Glass fiber reinforced concrete rock creates a product that appears realistic with the additional benefit of user-friendly installation methods.

The panels of varying thickness are molded from authentic rock formations with some manufacturers designing modular systems or self-contained waterfalls.

The castings are fixed to a solid structure, such as a block wall, or to rebar armatures and concrete is poured behind them. This bonds the castings to the primary structures. In instances where the panels are attached to rebar, foam blocks or the castings themselves are used as inner forms.

Installers must create the effect of continuous texture in the spaces between panels. This is accomplished by applying mortar over wire mesh and hand sculpting it. The entire installation then is colored.

The benefits of this method include ease of installation and realistic appearance. Because the castings are molded from actual rock formations, they are highly detailed. If a client requests the depiction of a particular type of stone and such panels are available, it’s the safest bet. The product also can be installed by less skilled workers and the construction time frame is shorter.

The primary drawback to the utilization of GFRC panels is cost. Because they originate with a pre-formed product, GFRC projects carry a higher price than those that employ hand-sculpted methodology. Some believe the extra detail is unnecessary on certain installations, reasoning that subtler lines and hues will be lost when viewed from far away. Additionally, this method is more restrictive because designers must select from the range of rock varieties replicated by the castings.


When working with GFRC panels, it’s important to adhere to best practices in order to obtain the greatest efficacy.

First, creative placement of panels will increase the design possibilities. An installer can use a variety of positions or trimming options to execute different effects. Even tilting the angle off vertical can alter the effect substantially.

To simplify construction, installers sometimes rely on the castings themselves to serve as forms. This method can be utilized when constructing the ceiling of a grotto.

Configure the rebar to create a template mimicking the outlines of the grotto, then cut panels with the template acting as a guide. Anchor the castings to the grotto walls and secure them with 4-by-4-foot lumber, placed vertically between the floor and ceiling, about 2 feet apart. Then pour the reinforced concrete directly on top of the castings, according to engineering specifications.

This method is only suitable for structures that will remain dry, such as garden walls or landscape steps. Waterfeatures, pool walls and other wet applications require a solid structure that is waterproofed before the panels are installed. Always check with the GFRC manufacturer because some systems require castings to be anchored to a structural wall.

Though the panels are knitted securely together from a construction standpoint, visually, the final project will resemble a jigsaw puzzle unless all protruding anchors are disguised with hand-textured mortar.

Continuity also must be considered when planning the placement of the panels. Leaving wider gaps between castings means fewer pieces are required and, while this can conserve resources, it also puts more responsibility on installers to hand texture those spaces, rendering them indistinguishable from the highly detailed castings.

When sculpting the gaps, it’s important to match the aesthetic of the panels as closely as possible. Continue all cracks and adhere to the same effects for detailing. For finer textures, utilize the stamping skins provided by some GFRC producers. Be sure to select a texture that resembles the style of casting.

The skins can be difficult to fit into corners and small spaces. In these cases, it may be more efficient to add texture by using paintbrushes or wrinkled tin foil. To effectively blend mortar and castings, the material should be feathered where they meet.

Finally, all panels and gaps should feature the same basic hue, so use a similarly-colored mortar. Avoid acid stains during the coloring phase, unless a primer coat is first placed underneath. Without an opaque undercoat, the sheer stains will display as different colors on the panel material and mortar.