Walker Art Center representatives who are in charge of the sculpture by Claes Oldenburg and Coosje van Bruggen had noticed some surface irregularities on the cherry and were concerned about the condition of its coatings. A failure analysis was performed by closely inspecting the cherry from a lift while it was still attached to the spoon. While the cherry had been repainted three previous times throughout the years, it was noted that the paint was fading, exhibiting slight discolorations, along with some microscopic surface cracking. These conditions were most likely brought on by more than 20 years of extreme conditions, such as temperature variations, UV rays from the sun and being exposed to water as the sculpture is part of a water feature. Because of that perfect storm for paint problems, and after being displayed for more than two decades, it was really a choice between refinishing the entire cherry or repairing different areas of the sculpture year after year.
After examining multiple options, Walker Art Center representatives decided to refinish the sculpture’s “cherry.” In February, they removed the cherry part of the sculpture and sent it by flatbed truck to Industrial Painting Specialists (IPS), a local coatings facility in Hugo, MN. Specifications were designed for how the cherry should be coated after taking several issues into consideration. Rob Roy, one of my NACE instructors who I’ve stayed in contact with throughout the years, was able to provide me with background information about the sculpture. Roy had consulted on the sculpture as it was being built in Connecticut. Networking through NACE helps professionals maintain the standards that are taught to them when they get their certification.
The sculpture is subjected to the harsh array of Minnesota conditions, such as temperatures that can range from more than 100 °F in the summer to -30 °F in the winter. When the temperature changes, the sculpture’s base metal, which is aluminum, can expand and contract through a process called coefficient of thermal expansion and contraction. If the sculpture expands in the summer and then contracts in the winter, the paint could present problems with adhesion at a microscopic level. The sculpture is also wet much of the time. It contains an internal watering system, which keeps the cherry looking shiny, but also creates harsher conditions for the coatings. It is for this reason that marine-grade immersion materials, which are often used to recoat yachts, were chosen for the project. Because the sculpture is displayed outdoors, it is subject to high ultraviolet conditions, which can cause problems such as fading and degradation for highly pigmented colors. Additionally, because the project is literally a piece of art, it had to look good.
The first step in the cherry’s refinishing was to remove all of the old coating materials by hand abrasive blast cleaning. This yielded a surprising insight into the sculpture, as it was discovered that the cherry was constructed of aluminum and not stainless steel as first thought. The Braun Intertec nondestructive examination (NDE) group used a testing method called positive material identification (PMI) to confirm the material’s type. In order to protect the aluminum, a first coat of Sherwin-Williams SEAGUARD MP multi-purpose epoxy primer was applied, followed by a coat of Sherwin-Williams SEAGUARD 5000 HS Epoxy to protect the primer. Each layer of coating material helps to protect the underlying layers.
Numerous layers of the fairing compound were applied in light coats before being sanded. This process was repeated several times until the final shape was accepted by Joe King, associate registrar of the Walker Art Center who served as the project manager of the cherry’s refinishing. After the final shape was accepted, the coating process began again. Another coat of Sherwin-Williams SEAGUARD 5000 HS Epoxy was applied over the fairing compound and the entire surface of the sculpture.
In late April, the cherry was finally ready to be painted with a Sherwin-Williams Pro-Line Y7001 deep gloss linear polyurethane red topcoat that was commissioned especially for the project and aptly named “cherry red.” Two coats of red polyurethane were applied, and the cherry was lightly re-sanded to remove any remaining surface imperfections or sanding lines. After the final red topcoat application, a final inspection and acceptance by King, the project manager, two coats of Y7001 linear polyurethane (untinted) clear were applied to discourage fading and aging from exposure to UV rays. The clear coat acts like a pair of sunglasses for the cherry. It helps make the red color last longer, which is important with such an iconic piece.
Tim Williams, a National Association of Corrosion Engineers (NACE)-certified Level 3 coatings inspector at Braun Intertec, performed the failure analysis, designed the specifications and oversaw the recoating of the “Spoonbrige and Cherry” sculpture, which is displayed in Minneapolis.
