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 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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Sources of the masonry salts

Sources of salt contamination include; 

  • Ground Water - through either lateral penetration or capillary rise 
  • Combustion gases in chimney flues contain  traces of acids which form chlorides, nitrates and sulphates in the masonry. This is a common source of contamination at the surface of chimney breasts and reveals at all levels (upper floors as well as ground floor level).
  • Prolonged leakage of tap water or central heating water.
  • Sea spray (or flood).
  • De-icing salt, de-ionising salt.
  • Leakage of soil water or contamination with urine.
  • Direct rain penetration through walls can results in an accumulation of sulphate on the internal face of walls. 


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?

Paper 1 – Types and Sources of Salts

  • Salts in porous materials: what are they and why are they bad?
  • Where are these salts coming from?
  • How do the salts interact with the environment?

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Paper 2 – Salts Distribution in Walls and Decay of Building Materials

  • How do the salts interact with the porous materials?
  • Types of damage and deterioration patterns

 Download Document >>  

Paper 3 – Salt Analysis: Diagnosis, Assessment and Treatments

  • This latest paper summarises the analyses from several laboratory and on-site tests of salt damage and the evaluation of treatments.

Download Document >>


A variety of damp related technical documents are available

For professionals looking to read a bit more regarding 'Codes of Practice, Guidance Notes and other Technical Documents towards dampness related issues, you can always visit our Damp Control Technical Library.  Alternatively, there is a variety of free dampness related CPD webinars below.

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Free training - Dampness related CPD videos

Want to learn more about salts and dampness?

For those professionals interested in learning more about the dampness, the reasons for why salts appear and how you can investigated and apply appropriate remedial damp treatments,  there is a variety of PCA training options for surveying professionals as well as technical/trade professionals. 

Use the search tool below to find available dampness related training courses or simply go to our training & qualifications section.  Alternatively, if you want to chat to someone, contract our training team on 01480 400 000 or contact them online.

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Surveying dampness in historic buildings

For more helpful information, help and advice specifically for professionals on surveying dampness in historical buildings, click the link below.

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Damp proof courses & membranes

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