Can you inspect for mold behind a wall?

Nov 2, 2018

Superman has x-ray vision, mold inspectors do not. So unless your inspector gains superpowers, how can they inspect obscured areas like inside of wall cavities for mold growth? We have a number of different options on how we can check the inside of wall cavities during mold inspections, ranging from totally noninvasive measures up to destructive methods.

Infrared Camera and Moisture Meter Inspections

An infrared camera is not x-ray vision and is not actually looking for mold. What an infrared camera is actually detecting is very small changes in surface temperature of the wall. If a material is wet, the water will evaporate from the surface of the material. Evaporation is an endothermic process, meaning that surrounding heat is absorbed in the process, which gets released. Because of that, the area where the evaporation is happening will appear cooler on the infrared camera image. However there are other causes for a cooler surface on a wall, so it is important to use a moisture meter to confirm that the surface is actually damp. Moisture is a key indicator of mold growth. Mold needs moisture in order to grow on building materials, so if you can find moisture, there is a high chance that there may be associated mold growth on that material. Because an infrared camera is detecting temperature, using a moisture meter in tandem with an infrared camera can help us rapidly assess a room for moisture, and find the areas where mold may be most likely to be growing in a wall cavity. A thorough moisture analysis is a key step in any good mold inspection.


A borescope is a tiny camera on a long flexible tube. A small opening, typically less than an inch across, can be cut into a wall to insert the borescope into the wall for observation. Attachments onto the end of the borescope can help direct the view to the reverse side of the wall. This method can be helpful in finding areas to cut into further or to sample from. However, due to obstructions such as insulation, general debris, and framing lumber, the borescope oftentimes does not give a clear view of the space.

Wall-Check Air Samples

Infrared cameras and borescopes are helpful tools in determining if there are any reasons for concern in walls, but they do not check for mold directly. To actually find out if there is mold growing in a wall cavity, a laboratory sample is needed. The least invasive way of collecting a sample inside a wall cavity is to take a wall-check sample. A wall-check is an air sample that is collected directly from inside the wall cavity. Once a site is selected a small hole, the diameter of a pencil, is drilled into the wall. An inner wall sampling attachment is put inside the hole to pull air from the wall cavity. Since only a small hole is needed, this minimizes the repair and potential exposure risks. Some limitations from wall checks are that they only test a small area of the wall cavity since studs and other obstructions can block free airflow inside the wall cavity, so proper site selection and a little bit of luck are crucial. It is also very easy to “overload” the sampling media with drywall dust and other debris, making it very difficult for the laboratory to analyze.

Invasive Visual Mold Inspections

The most conclusive way to find out if there is mold growing in a wall is to cut into the wall for a visual inspection. This can be a small opening just to get a flashlight and mirror inside, all the way up to entire sections of the wall. Proper containment and personal protective equipment should be used when doing this type of inspection to avoid possible dispersal of airborne mold and worker exposure. Also, inspectors should be aware of any possible asbestos or lead paint risks before cutting into walls, and to have suspect materials tested beforehand. With the walls opened up, and discolored area can be sampled. This type of testing will require repairs that most mold inspectors are not equipped to do, so it is a good idea to have a contractor ready to patch the walls back up afterward.

Each mold issue is unique, so an experienced inspector will need to use one or more of these methods to assess potential mold issues in enclosed spaces. If you have concerns with potential mold in a wall, or any other mold concern, contact us to discuss what our team can do to help.

Additionally here are some videos explaining how we can test inside wall cavities.