Finding Leaks Before They Leak
By Ken VanBree
In my last column, I introduced infrared imaging and showed how it could be used to check for water leaks. Thermography can also be used to find latent defects that will turn into future water leaks.
A certain class of building defects continues to plague the construction industry despite a variety of defensive techniques put in place to prevent them. These defects occur when a nail or screw comes into contact with a copper water pipe and the problem isn't immediately detected. Galvanic action between the steel fastener and the copper pipe or oxidation of the fastener will eventually lead to a hole in the pipe; however, it may take months or years for the leak to develop.
Thermal imaging can be used to detect this class of latent defect before it becomes an ex- pensive water leak or mold remediation. The technique relies on the high conductance of the metal screws or nails. By running hot water through the pipes, a metal fastener that is in contact with a water line will heat up more quickly than the surrounding wall board, providing a hot spot easily observable with an infrared camera.
The nearby picture shows four views of a test wall that illustrate the technique. The upper left image shows the wall after wall board has been installed but be- fore tape and mud has been applied. The wall board screws are clearly visible. In the image on the upper right a thermal image of the wall has been superimposed on the first image. The thermal overlay shows that three of the screws are much hotter than the surrounding wall board. The reason is because these screws are in contact with a water pipe in the wall that is carrying hot water.
The image in the lower left shows the back side of the wall where a screw is resting on the water pipe without penetrating it. In the image on the lower right the additional screw is clearly visible in the thermal image. This last image also shows that the wall board screws are still visible in the thermal overlay despite the fact that they are covered with taping mud. The mud was still wet in this image, which accounts for the dark (cooler) streak on the right side of the thermal overlay.
The test wall in these images was built to develop the techniques for locating latent construction defects. Additional details on the technique and its application to real world situations are given in a paper entitled "Using Thermography to find a class of latent construction defects" given at InfraMation 2005. A copy of the paper can be downloaded from our website at: www.imagingperspective.com.
June 2005 Builder Architect Edition Issue