Unlike objects housed in a museum, sculptures installed outside face a variety of environmental factors. Along with gathering dirt, spiderwebs, and the ever-unpleasant bird droppings, outdoor art is also subject to the weather. Conditions including extreme fluctuations in temperature, UV light, and excessive moisture can contribute to the deterioration of public art. In the case of Sol LeWitt’s Circle with Towers, water movement through the structure resulted in several recurring maintenance issues. In order to mitigate future damage, RILEM tube testing was undertaken to assess the efficacy of a water-repellent coating.
Built of concrete masonry units (CMU) and grey pointing mortar, Circle with Towers by Sol LeWitt was installed on UT Austin’s campus in 2012. Located outside of the Bill and Melinda Gates Computer Science Complex and Dell Computer Science Hall, the structure consists of a circular base with eight vertical towers. After construction, orange-pink stains began to show on the surface of the masonry. Conservators and staff also identified areas of efflorescence (the formation of salt crystals on a masonry surface), cracks throughout the pointing mortar, and dark stains across the sculpture. The structure, along with the surrounding environment, was examined by conservators and a forensic building engineer in order to determine the root cause of these issues. They found that water movement through the absorbent CMU was to blame for the range of poor conditions. As a result, they recommended applying a water-repellent coating to the surface.
The purpose of applying a water-repellent coating to the sculpture is to reduce the absorbency of the CMU, effectively minimizing water movement and its harmful consequences. In order to assess the success of this coating, it was necessary to first establish the absorption rate of the individual masonry blocks and overall sculpture prior to and after treatment. Established in the 1980s by the International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM, based on the French name) the RILEM tube test was chosen to calculate the absorption rate of the material. The test utilizes a special graduate cylinder style tube with a wide lip, which is attached it to a wall using removable putty. Water is then added to the cylinder and any change in volume is then tracked over a set period of time.
Prior to testing, a proposal was developed by MSHP students Sydney Landers and Ali Wysopal, with guidance from conservator Izabella Nuckels, outlining the purpose and scope, methodology, and testing procedures to be followed. After receiving approval from Landmarks, testing was carried out by Ali Wysopal.
In part to establish efficacy as well as to assess any visual alterations made to the concrete, initial water absorption tests were performed on uncoated and coated portions of a sacrificial CMU. This precaution ensured that no aspect of the test would harm the material before testing on the sculpture itself.
The preliminary test results showed that the repellent coating effectively reduced the absorbency of the CMU, with the coating causing only a slight darkening of the block's surface. Based on these results, it was determined that the water-repellent was effective and plans were made to apply the coating to the sculpture. In tandem with this treatment, a second and third round of testing was carried out on the untreated and treated sculpture. These subsequent tests were performed in order to establish the absorption rate of the structure before and after the application of the water-repellent coating. As predicted, the coating lowered the absorption rate substantially. Results showed the average absorption rate of the newly coated sculpture to be under 0.004 mL per minute, in comparison with the uncoated object which had an average absorption rate of 1.3 mL per minute.
To ensure that this new, lower absorption rate is maintained, Landmarks collections staff will need to perform a RILEM test annually following the procedures outlined in the proposal. Over time, it is expected that this repellent will begin to wear away and lose its ability to repel moisture. If left untreated after this breakdown occurs, the previously noted deterioration issues will return. By tracking the masonry’s absorption rate, Landmarks staff can remain apprised of the coating's durability, thereby helping to ensure the long-term preservation of the sculpture.