Salts in Masonry Walls

 Salts in Masonry Walls

In certain circumstances/scenarios, salts within a property can lead to the cosmetic and physical deterioration of building materials and the appearance of damp patches. 

The salts which cause the dampness problem are chloride and nitrate salts of sodium and sometimes, calcium. These salts are hygroscopic (or in some cases, deliquescent) and because of this, they are seldom visible.  

The dampness, due to their presence, becomes apparent when the humidity in the building is high.  Sometimes the dampness will appear when the room is humid and disappear when the air is dry.  The amount of water absorbed by salt contaminated masonry, mortar or plaster will vary with the humidity of the air and the amount and character of the salt. 

Salts which are visible as efflorescence are seldom hygroscopic and are usually sulphates. 

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Getting technical about salts

For those interested in learning more about hygroscopic salts, in 2020 PCA’s Dr Paula Lopez-Arce released a set of short papers focussing on salts in porous construction and building materials. These papers aim to provide a better understanding of the problems which affect the durability of many types of buildings, materials and structures in all kind of climates and weather conditions. They focus on questions often raised such as 

• Type and sources of salts / Decay of building materials: Why are salts important? Where are they coming from? How do they interact and behave with the environment and the building materials?
• Concentration, distribution and measurement techniques: Where are the salts localised? How can we identify and measure them?
• Remediation solutions: Which remediation actions can be taken? Are these effective?