Guide to damp related salts in buildings

Sources and Behaviour

• Found in the ground and can rise into walls via capillary action.
• Accumulate at the point of maximum moisture rise, forming a "salt band."
• Commonly seen on chimney breasts due to rainwater leaching through soot.
• Found in barns used for housing animals due to urine containing chlorides.

What are Hygroscopic Salts?

Types of Hygroscopic salts

• Nitrates (NO3)
• Chlorides (Cl-)

Hygroscopic salts, such as nitrates (NO3) and chlorides (Cl-), are soluble salts present in the ground. They can access a property when moisture from the ground rises into walls via capillary action. These salts accumulate at the maximum height of the rise, forming a "salt band." This phenomenon is commonly seen on chimney breasts where rainwater has leached through soot and in barns used for housing animals due to the presence of chlorides in urine.

Indications of hygroscopic salts typically appear as flat damp patches where paintwork isn’t blistering or spalling. These patches can be mistaken for recent water ingress or leaks. Because hygroscopic salts absorb moisture from the air, addressing the source of moisture and replacing affected plaster is crucial. A simple test to identify the presence of these salts involves boiling a kettle repeatedly in the room and observing if the damp patches worsen. Additionally, nitrates and chlorides trigger conductance moisture meters.

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What are Efflorescent Salts?

Types

• Sodium Sulphate (Na2SO4)
• Magnesium Sulphate (MgSO4)

Efflorescent salts, such as sodium sulphate (Na2SO4) and magnesium sulphate (MgSO4), are commonly found in building materials and groundwater. These salts dissolve in water moving through a structure and re-crystallize upon evaporation, forming white crystalline deposits. This process often causes paint to delaminate and spall. Unlike hygroscopic salts, efflorescent salts do not absorb moisture from the air and do not trigger conductance moisture meters. Addressing the source of moisture, removing surface salt deposits, and monitoring any physical damage are key steps in managing efflorescent salts.

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Free Lime

Free lime, or calcium carbonate (CaCO3), forms when significant water movement over new concrete leaches lime and mineral salts. This is most commonly seen in wet basements with new concrete. The water dissolves calcium hydroxide from the concrete, which reacts with carbon dioxide to form calcium carbonate. This then precipitates as a solid deposit when the water evaporates, appearing as an off-white limescale-like deposit.

Expert Help from Trace Basement Systems

Trace Basement Systems specialises in diagnosing and treating salt-related damp issues in buildings. Their expertise covers all types of salt contamination, including hygroscopic salts, efflorescent salts, and free lime. They offer comprehensive solutions that include identifying the source of moisture, removing affected materials, and implementing long-term preventative measures to protect your property from future salt damage.

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Conclusion

Understanding and identifying different types of salts in buildings is crucial for addressing moisture issues and maintaining the integrity of the structure. Proper diagnosis and remediation can prevent further damage and preserve the property. For professional assistance, consider consulting Trace Basement Systems, experts in managing and mitigating salt-related damp problems.

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Author

James

Note: This guide aims to provide a concise overview. For more detailed information, refer to specific studies or consult a professional.

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Trace understand problems of moisture in buildings, if you have requirements or questions, please contact us.