Module 4 · Evidence-Based Diagnosis
4.3 Salt Analysis in Practice
8 min read
Module 1.4 established why salts matter: they hold moisture from the air, so a wall can read persistently damp with nothing arriving. This lesson is the practice — where to sample, how to run the test, and how to read a result that is semi-quantitative rather than a laboratory number. It is the cheapest test in the toolkit and the one that most often changes a diagnosis.
Learning objectives
By the end of this lesson you will be able to:
- Sample for salts at the right locations and depths.
- Run a semi-quantitative field test and interpret its bands correctly.
- Combine salt results with moisture content to separate hygroscopic from active moisture.
- State a salt finding in a report without overreaching what the method supports.
Key terms
- Semi-quantitative
- Producing a concentration band rather than a precise figure. Adequate for the diagnostic question, and must be reported as a band.
- Salt profile
- How salt concentration varies with height and depth. Where the salts are concentrated marks where evaporation has historically occurred.
- Nitrate
- Strongly hygroscopic salt from organic decomposition. Its presence indicates prolonged contact with ground water carrying those products.
- Sulphate
- Usually from the masonry, cement or flue gases. Not usefully hygroscopic, but expansive — the agent of sulphate attack.
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