Hygroscopic Salts & Damp Misdiagnosis
Hygroscopic salts are one of the most misunderstood causes of apparent dampness in buildings. They are frequently responsible for persistent moisture readings, damp-looking walls, and repeated misdiagnosis — even when no active damp source exists.
Understanding how hygroscopic salts behave is essential to diagnosing damp correctly and avoiding unnecessary remedial work.
What Are Hygroscopic Salts?
Hygroscopic salts are naturally occurring mineral salts that attract and retain moisture from the air. Once present within plaster or masonry, they can cause walls to appear damp even when no liquid water is entering the structure.
These salts are commonly introduced into walls through historic moisture, previous damp issues, or ground contamination and can remain active long after the original source of moisture has been resolved.
How Hygroscopic Salts Cause False Damp Readings
Hygroscopic salts readily absorb atmospheric moisture, particularly in humid conditions. This absorbed moisture can trigger elevated readings on moisture meters, giving the impression of ongoing dampness.
In reality, the moisture is being held by salt contamination within the wall rather than entering the property through rising damp or penetration.
Why Moisture Meters Can Be Misleading
Many damp assessments rely heavily on resistance-based moisture meters. These tools react to conductivity within materials, which is significantly influenced by salt content.
As a result, salt-contaminated plaster can produce high moisture readings even when the wall is structurally dry. Without understanding this limitation, hygroscopic salts are often mistaken for active damp.
Common Situations Where Hygroscopic Salts Are Present
Hygroscopic salts are commonly found in:
• Older properties with a history of damp
• Walls previously affected by rising damp
• Areas where damp proofing work has been carried out in the past
• Solid wall construction with original plaster
• Properties with long-term condensation issues
In many cases, the original damp issue may no longer exist, but the salts remain.
The Link Between Hygroscopic Salts and Misdiagnosis
Hygroscopic salts are a major contributor to damp misdiagnosis. Walls affected by salt contamination can repeatedly be labelled as damp, leading to unnecessary chemical damp proof courses, replastering, or other invasive work.
Without addressing the presence of salts or understanding their behaviour, treatments often fail to resolve the perceived problem.
How a Proper Damp Survey Identifies the Difference
A proper damp survey considers the presence of salts alongside building design, ventilation, moisture sources, and environmental conditions.
By assessing patterns, context, and history — rather than relying solely on meter readings — it is possible to determine whether moisture is active or being attracted by hygroscopic salts.
Why This Matters
Treating salt contamination as active damp leads to wasted money, unnecessary disruption, and ongoing frustration.
Understanding hygroscopic salts allows damp issues to be diagnosed accurately, ensuring that any recommendations are genuinely required and effective.
Concerned About Persistent Damp or Conflicting Survey Results?
If you’ve been told damp is present but the issue never seems to resolve, hygroscopic salts may be a contributing factor.
An independent damp survey can help identify the real cause and prevent unnecessary work.