The Watts Tower was created by Sabato Rodia from 1921-1954 and was constructed without the use of mechanical methods. It is composed of Portland cement, steel, ornamentation (glass, tile, stones, sea shells), wire mesh, and armature. Now a National Historic Landmark, the towers and other sculptures are showing signs of deterioration and material loss. Beginning in 2011, the Los Angeles County Museum of Art (LACMA) and the City of Los Angeles collaborated to conduct a materials evaluation in order to update the conservation plan and identify a new maintenance routine. Initial observations and investigations identified some of the issues to be mortar cracking, loss of ornament, armature corrosion from past treatments, adhesive and cohesive failures, and incompatibility of repair materials (i.e.,hydraulic cement, Portland cement, and traditional materials). The conservators wanted to better understand what repairs were successful and new causes of deterioration.
The team established a hypothesis that included multiple contributing factors to the deterioration of the towers. These factors included environmental concerns such as seismic and wind loads, but also thermal expansion, stresses, and moisture intrusion. Adjoining materials with different rates of thermal expansion led to the eventual detachment of ornamentation. With support from the UCLA engineering department, the team utilized displacement monitors to monitor the cracks in the tower. The team also employed infared thermography to visualize the heat profile of the central tower while also using time lapse photography. The results indicated that there was an uneven heating and cooling of central core. In conjunction with the displacement monitors, a tilt meter, accelerometer and thermocouples were used to measure the displacements caused by the thermal loading. It was determined that the central tower had a north tilt due to thermal expansion during the day. The accelerometer data also showed an increase in vibration frequency with change in temperature.
Another concern were the wind loads caused by the Santa Anna winds hailing from the deserts in the months of October through March. The winds caused ornament loss due to increase of movement and vibration. It was also determined that new cracks formed and existing cracks widened and narrowed during wind events. A dynamic wind sensor and weather station were used to monitor rain, temperature, humidity, and wind speed. The sensors confirmed that wind and seismic activity affected the tower, tilting the tower in correlation with wind speed. Two wind events in October 2012 and January 2013 corresponded with the base crack displacements.
The team concluded that it was necessary to accept that movement occurs and that re-treatment is necessary. To limit the amount of necessary intervention, it was important to use flexible repair materials that allowed for movement, such as elastomeric crack fillers. Polymer modified mortars with lower modulus of elasticity and flexible adhesives for ornament would also allow for movement. The treatment plan also included initiatives to slow the corrosion rate, increase the water repellancy and to modify the environment to provide a wind break northeast of the towers. It is also necessary to re-scan the tower every five years to determine if long term displacement has occurred.
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AIC Blog Archives: Conservators Converse
Former Blog of the American Institute for Conservation