How to Apply a Chain Shell Coating on a Monolithic Dome
Exterior concrete coating, or chain shell coating, on the 20-foot conference dome.
In 1999, the 20-foot diameter conference dome at the Monolithic Dome Research Park got a “face-lift” by covering the exterior with fencing and coating it with shotcrete. In addition to providing a new look for the dome, a shotcrete coating will last indefinitely and provide a strong, maintenance-free exterior to your dome. We call this coating method—the Chain Shell.
First, thoroughly clean the Airform. The Airform needs to be dry to the touch before applying shotcrete. Then, attach additional molding around windows and doors. The molding serves as an extension of the existing molding and provides a depth measurement or stop-spray guideline for shotcrete being sprayed.
Figure 1. Placement of the chain-link fencing on the clean dome.
Cover the dome with chain-link fencing (Figure 1). We recommend chain-link fencing because it molds to the dome shape better than chicken wire and provides non-structural reinforcement to the shotcrete coating.
Figure 2. The chain-link can be connected using hog rings, cable ties, or tie wire.
Connect the pieces of chain-link by using hog rings, cable ties, or tie wire (Figure 2).
Figure 3. Protect openings and other accessories with plastic.
Mask windows, doors, openings, air conditioners, etc., with plastic to protect from overspray (Figure 3).
Figure 4. Apply an initial ½ inch of shotcrete over dome.
Spray the shotcrete. Initially, a ½-inch cover coat should be applied (Figure 4).
After the cover coat is set, spray enough shotcrete to cover the chain-link fencing, approximately 1 ½ to 2 inches total thickness.
Figure 5. Allow adequate curing time between shotcrete applications.
Curing time is dependent upon weather conditions. Allow adequate time between shotcrete applications (Figure 5).
Figure 6. Approximately 1 ½ to 2 inches of shotcrete will be applied to completely cover the fencing.
On an average day, we spray one coat per day on a large dome. By beginning early in the morning, you should be able to spray a second coat on a small dome by late afternoon (Figure 6).
When the chain-link is completely covered with shotcrete, clean up the overspray by trimming, molding, shaping and shaving the shotcrete.
Figure 7. Spray the final coat. A powdered colorant may be added to the final mix to provide color.
To add color to the final coat, a powdered colorant can be added to the shotcrete mix. Spray the final coat (Figure 7).
Figure 8. A concrete stain with a sealant can be applied when the final coat of shotcrete is cured.
When the exterior is completely set, the shotcrete can be left as sprayed, but a clear concrete sealant must be applied. A concrete stain with a sealant or exterior paint can be rolled onto the cured finish (Figure 8).
It is vital to clean your concrete pump after each use and perform necessary maintenance according to the owner’s manual when the job is complete.
Reprinted from the Winter 1999 issue of the Roundup: Journal of the Monolithic Dome Institute