Module 4 · Evidence-Based Diagnosis
4.5 Thermography and Its False Positives
9 min read
Thermal imaging is the most persuasive-looking evidence in damp surveying and among the most frequently misread. The images are vivid, clients find them compelling, and what they actually show is surface temperature — from which moisture is one of several possible inferences. Used for the questions it answers well it is genuinely decisive; used as a moisture detector it manufactures confident errors.
Learning objectives
By the end of this lesson you will be able to:
- State what a thermal image physically records.
- Identify the questions thermography answers well.
- Recognise the common false positives and false negatives.
- Set up an inspection so an image means something.
Key terms
- Emissivity
- How efficiently a surface radiates thermal energy. Varies by material and finish, and an uncorrected mismatch produces apparent temperature differences that are not real.
- Thermal gradient
- A temperature difference across the element being imaged. Without one, there is nothing for the camera to show.
- Evaporative cooling
- The temperature drop at a surface where water is evaporating. The mechanism by which damp sometimes appears cool on an image.
- Thermal mass effect
- A dense element responding to temperature change more slowly than its surroundings, appearing anomalous for reasons unrelated to moisture.
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