Seeing Beneath the Skin
In the 1960s, among the products advertised in the backs of comic books—“Live Sea monkeys!” and “Trick Black Soap”—were “X-Ray Specs.” For only one dollar, these glasses supposedly let you look through your hand to see the bones, or perhaps under the clothes of your friends. Whether the glasses worked or not, none of us at ARG knows, because of course we never ordered them. But recently, ARG Conservation Services acquired a thermal camera that fulfills the promise. It cost a great deal more than a dollar, but it offers us a much more tantalizing ability: the capacity to “see” beneath the skin of buildings.
Infrared photography is a powerful diagnostic tool that can help us understand what’s going on within a building envelope. Essentially, the thermal camera creates an image of the heat radiated by different areas and components of a building. Often, where a wall has been opened up in the past for repair and then patched and plastered over, the area is visually indistinguishable from the surrounding solid wall. But the patched area will radiate heat differently, so the infrared camera can tell us where the opening was—and let us know that’s not a good place to drill a core for seismic reinforcement.
If a portion of a wall or foundation is cooler than its surroundings, that may mean it is saturated with water, something not always detectable by the naked eye. This can be very useful in learning where we need to repair cladding materials or stop a leak.
With historic buildings, often the original drawings have long been lost. Even if they exist, the original structure may have been changed or damaged since the drawings were made. The thermal camera can help us identify the location and condition of structural elements, such as reinforcing bar and concrete.
We’re already using it in a number of projects. For the local broadcast station KPIX, we’re trying to understand the performance of past building repairs and determine areas where there might be moisture build-up. On another project, we’re using it to help us identify where steel might be corroding.We used it just recently at the Elks Club to zero in on the location of a water leak in the facility’s pool. In preparation for the seismic strengthening of San Antonio Mission at Fort Hunter Liggett in Monterey County, the thermal camera helped us discover windows that had been plastered over. They were indistinguishable from the rest of the wall, but beneath the plaster, they were just voids. If we hadn’t detected them, and the structural engineer started drilling cores in those locations, construction would have to stop, the rig would have to be moved, and everything would have to be replanned. The savings in change orders can be huge.
The thermal camera is just one more diagnostic tool in our bag of tools, of course. We use it to confirm or identify areas that might need more exploration and research. Two of us took an extensive training course from the camera’s manufacturer to learn how to analyze the data. Once we’ve studied the thermographic images, we might decide to engage in exploratory drilling or bring in a moisture meter.
A lot depends on the time of day we take the thermal photo, too, so we have to figure out ahead of time whether a given situation would be best photographed in the evening or in the morning. Different sides of the building heat up and cool down at different times. We have to decide which conditions will give us the shot that shows us the most information.
Thermal cameras have a wide range of uses—contractors use them to identify electrical issues, and medical professionals use them to diagnose circulation problems. As far as we know, we’re the only preservation firm that has one. We’re still discovering new ways we can use it to enhance the services we offer.
Now if we could only figure out how to keep our sea monkeys alive.