OUTDOOR SCULPTURE CONSERVATION at THE OHIO CONSERVATION CENTER: Outdoor sculpture conservation is one of our most active specialties. In 2014 we removed to our facility a monumental outdoor sculpture by James Rosati (1911-1988) for complete repainting. This was our second time handling this large outdoor sculpture aluminum artwork. The first time was when we were asked to install it after it had been repainted, purportedly, by a conservator.
The work, Heroic Shorepoints I, was commissioned for, and is sited at, the Health and Human Services (Hubert H. Humphrey) Building in Washington, DC. It was commissioned by the United States General Services Administration.
After a number of years following our installation of the outdoor sculpture some of the red paint began disbonding in sheets. Adhesion of coatings to aluminum is tricky and requires chemical treatment of the freshly blasted metal to form a stable oxide to which primers can adhere. Skipping that chemical treatment can lead to poor adhesion.
Our inspection of the exposed aluminum where the priming layer disbonded showed no evidence of an optimal 1.0-2.0 mil blast profile, nor was the metal discolored – possibly that being evidence of no chemical pre-treatment.
The past work had to be repeated and done properly this time. We worked with United Rigging company, as we often do, to crane this outdoor sculpture onto a truck and drive it to our blast and coatings facility in Oberlin.
There, after each section was abrasive blasted to remove existing coatings and provide an optimal surface profile, the metal was immediately chemically treated.
In the past, and still continuing today to a reduced degree, hexavalent chromate conversion coatings were used to prepare aluminum for coatings. The hexavalent chromium is a known and serious carcinogen. In the past we have used Alodine 1202, but only on a small scale. We may never use that conversion coating again now that safer alternatives are showing promise.
In its place, we used Pantheon’s PreKote for the initial preparation of the bare aluminum. PreKote cleans the surface to be painted while enhancing the adhesion of coatings and improves corrosion protection – all with a superior, non-hazardous and safe technology. This easy-to-apply process deposits a molecular layer that bonds to the surface of metal or composite material. This layer allows the coating, when applied, to get closer to the substrate surface than traditional pre-treatments creating a stronger bond with the surface.
PreKote also provides a polar/non-polar molecule that attaches itself to permanently embedded contamination; this molecule attracts the coating. In contrast, traditional conversion coatings containing heavy metals such as chrome or zinc have no mechanism by which to attach themselves to permanently imbedded contamination. Since the coating cannot attach itself to those areas, it is a common cause of coating blisters, out-gassing (pinholes), skips, etc.
After the PreKote treatment, a conventional epoxy and acrylic urethane coating system was used to finish the outdoor sculpture in its original color.