I work in building conservation, and I would say that for this property with lime pointing, the ‘damp proofing’ will cause more trouble than you started with. It never works in my opinion, but just masks the problem. I’d guess the reason the moisture showed itself at the base of the chimney is because it was condensating and running down the flue walls, gathering at the bottom, so they thought rising damp. Also causes problems using wallpaper inside and vinyl paints (particularly external walls), if you used breathable paints the moisture would breathe out or in through the entire wall not just in patches. In this case, I would also recommend that ALL flues of the chimney are vented sufficiently at the top and bottom. Warm dry air from the interior will travel up the flue and be released at the top vent, carrying with it the moisture, therefore reducing RH on the flue walls. Even better….install a woodburner but vent the flue if it’s lined. The patch extends across the chimney breast because of the flue(s) for the flats below passing the fireplace shown. I’ve seen evidence of it on past work and have resolved it by this method. Old houses were built with old materials, so if you only use them, the house will not have problems. Stain blockers and waterproof materials just hide it and it will then be ongoing, which is unhealthy for occupants and the house. We spend much time undoing the problems caused by modern materials and illogical ‘damp proofing’ measures. Blocking it would be a nightmare to undo, and the bricks and lime externally will never breathe out the trapped moisture with all that gunk injected in there.
Thank you for your detailed and insightful comment! 😊 I completely agree with you, especially regarding the issues caused by modern damp-proofing measures. 🏠 In cases like this, the real culprit is often hygroscopic salts - they’re not a source of moisture but typically result from the historic burning of coal. When chimneys become damp (due to replastering, a leak, or other moisture intrusion), these salts are released and can cause patches of damp. However, the temporary moisture is just a trigger, not a root cause, the root cause being the salts - agin it is not a source of moisture, so can't cause mould, rot or any damage to the properties structure. You can read more about this here: 🔗 damp.ai/hygroscopic Key Points to Address the Issue: Replastering Isn’t the Solution if there iOS a source of moisture: Simply replastering won’t solve the underlying problem. These methods mask the issue rather than fix it and can trap moisture, risking rot, making things considerably worse. The trouble comes if there is an actual source of moisture, be that condensation or leak, the damp proofing makes it worse. Condensation in the Flue: You’re right that moisture can condense inside the flue, typically because the flue is thinner than then main external wall. This can be mistaken for rising damp, leading to unnecessary and damaging treatments. Breathable Materials: Using breathable paints and materials like lime plaster allows moisture to move freely in and out of the walls. Vinyl paints and modern materials trap moisture and lead to ongoing problems. 🎨🧱 Avoid Damp-Proofing Injections: Injecting damp-proofing chemicals into walls, especially with lime pointing can be disastrous. It damages the wall, traps moisture, damages the breathability of the structure, will always look unsightly and is extremely difficult to undo. A Practical Alternative for Hygroscopic Salts By the way, while I recommend using an oil-based primer to cover hygroscopic salts, I recognise that this approach shares some similarities with what damp-proofers do. However, there are three key benefits: Easily Removable: If hygroscopic salts are misdiagnosed and there is, in fact, a source of moisture, the primer can be removed without major disruption. 🛠️ Minimal Coverage: The primer only needs to be applied to small areas, not wall-to-ceiling, so it won’t significantly impact the breathability of the wall. 🧱💨 Cost-Effective: It works much better than damp-proofing at hiding hygroscopic salts, without the need for destructive work, and for a fraction of the price. 💰✅ A Holistic Approach: Old houses need to be treated with respect for their original materials and design. When you stick to lime, breathable finishes, and proper ventilation, these buildings perform beautifully. Modern interventions often create more problems than they solve - as you said, it becomes an unhealthy situation for both the house and its occupants. Thanks again for sharing your experience - the more we educate homeowners and professionals, the better we can protect these beautiful historic buildings! 🏛️✨ Best of luck with your work in conservation, Simon 🌐 Try our AI tool: damp.ai - feedback is always welcome! 😊
Thank you for your kind words! 😊 I’m glad you found the information helpful. It’s surprising how often hygroscopic salts are mistaken for rising damp, especially on upper floors like chimney breasts where rising damp can’t occur 🏠💧. Understanding these subtle differences can save a lot of unnecessary treatment and expense 💸. If you have any questions or specific damp issues you'd like advice on, feel free to use damp.ai - always trying to help solve the root cause of damp, not just the symptoms! 🤝
A good way to find this hygroscopic salt dampness on old chimney breast walls, is to humidify the room. Even boiling a kettle can make them show up. On property surveys we spend a bit of time looking for these areas, because even if they are visually unseen on the day of the survey, they always show up on a standard resistance type damp meter. Great videos as always & very informative, even to other surveyors.
Thanks for the great tip, Nigel! 🙌 Humidifying the room (or boiling a kettle ☕) is such a practical way to highlight those hygroscopic salt areas! 🔍 While some people call these walls "contaminated," I don't - they aren't a source of moisture 💧, mould 🦠, or rot 🍂. It's really just a feature of the salts. Covering them up is simple! 🛠️ I usually recommend an oil-based primer 🖌️ because it's affordable 💷 and easy to apply. But any impermeable coating works, even insulation! 🏠 Thanks again for the kind words and for sharing your insight! 👍😊
@@dampsurveys the biggest issue with this type of chimney salt damp staining is that they look unsightly. You pay £100's of thousand buying a property, or you spend £1,000's on decoration, only for these patches to randomly appear & sometimes disappear. Is a very misunderstood phenomena that I see often. It confuses, surveyors, builders, architects & other professionals regularly.
Thanks, Nigel-what an insightful observation! 😊 I completely agree. Hygroscopic salts are often misunderstood, leading to unnecessary and expensive treatments. The rising damp industry has built an empire on this misunderstanding, costing the UK billions annually. If we could spread the word about what’s really happening with these salts, we could collectively save £2 billion a year. Please do help amplify the message! What Are Hygroscopic Salts? Hygroscopic salts are not a source of water themselves. They exist in a state of dynamic equilibrium, continuously absorbing moisture from the air when humidity is high and releasing it when humidity is low. This constant exchange creates visible damp stains that appear and disappear based on environmental conditions like temperature and humidity. Why They’re Misleading: 1️⃣ Not Drying Water Unlike water from leaks or condensation, the moisture associated with hygroscopic salts doesn’t behave in a predictable way. It’s linked to changes in the surrounding air and doesn’t leave a cooling thermal signature like actual drying water would. 2️⃣ Triggering Factors Hygroscopic salts are often mistaken for signs of rising damp, but they are brought to the surface after damp events, such as: 🧪 Chimney removal or replastering. 🧪 Leaks or rainwater penetrating damp. 🧪 Intense condensation. 🧪 Damp-proofing treatments, where slurry is applied to slightly moist walls. 🧪 I’ve even seen cases where dry lining was installed using aqueous adhesive, causing the salts to activate and show through. Using an expanded foam adhesive would have avoided this issue entirely. 3️⃣ Unsightly but Harmless While the stains are unsightly, they rarely indicate a structural issue. Treating the walls with oil-based primers, like Zinsser Cover Stain, is often more effective than removing the plaster entirely-especially if the underlying wall is already dry. Managing Hygroscopic Salts 🔎 Step 1: Eliminate Moisture Triggers Ensure there’s no ongoing source of moisture, such as: 🎨 Leaks in the chimney or roof. 🎨 Penetrating damp from rain. 🎨 Poor ventilation leading to condensation. 🔎 Step 2: Monitor and Confirm Use data loggers to track humidity levels around the affected area and confirm the environment is dry before applying treatments. 🔎 Step 3: Treat the Aesthetic Issue Apply Zinsser Cover Stain with a 300mm overlap to seal the visible stains. This approach avoids over-application, which can inhibit the wall’s breathability. Suggested Videos: 1️⃣ "Hygroscopic Salts Triggered by Rain Part 1" - th-cam.com/video/HJR7MqbnRZ4/w-d-xo.html 2️⃣ "Hygroscopic Salts Triggered by Rain Part 2" - th-cam.com/video/cRVhGlNmT3I/w-d-xo.html 3️⃣ "Hygroscopic Salts Triggered by Rain Part 3" - th-cam.com/video/KykkQ4u_siE/w-d-xo.html 4️⃣ "Damp on Chimney Breast" - th-cam.com/video/LgkJcD5FTgc/w-d-xo.html Let’s Spread the Word! This is an incredibly misunderstood phenomenon that confuses surveyors, builders, architects, and more. But together, we can demystify damp. Visit damp.ai for more insights, and don’t forget to subscribe to my channel for daily videos addressing real-world issues like this. 🌟 📚 Coming Soon: My eBook this summer will cover these topics in greater depth, helping homeowners and professionals alike to make informed decisions. Stay tuned! 🚀
I work in building conservation, and I would say that for this property with lime pointing, the ‘damp proofing’ will cause more trouble than you started with. It never works in my opinion, but just masks the problem. I’d guess the reason the moisture showed itself at the base of the chimney is because it was condensating and running down the flue walls, gathering at the bottom, so they thought rising damp. Also causes problems using wallpaper inside and vinyl paints (particularly external walls), if you used breathable paints the moisture would breathe out or in through the entire wall not just in patches. In this case, I would also recommend that ALL flues of the chimney are vented sufficiently at the top and bottom. Warm dry air from the interior will travel up the flue and be released at the top vent, carrying with it the moisture, therefore reducing RH on the flue walls. Even better….install a woodburner but vent the flue if it’s lined. The patch extends across the chimney breast because of the flue(s) for the flats below passing the fireplace shown. I’ve seen evidence of it on past work and have resolved it by this method. Old houses were built with old materials, so if you only use them, the house will not have problems. Stain blockers and waterproof materials just hide it and it will then be ongoing, which is unhealthy for occupants and the house. We spend much time undoing the problems caused by modern materials and illogical ‘damp proofing’ measures. Blocking it would be a nightmare to undo, and the bricks and lime externally will never breathe out the trapped moisture with all that gunk injected in there.
Thank you for your detailed and insightful comment! 😊 I completely agree with you, especially regarding the issues caused by modern damp-proofing measures. 🏠
In cases like this, the real culprit is often hygroscopic salts - they’re not a source of moisture but typically result from the historic burning of coal. When chimneys become damp (due to replastering, a leak, or other moisture intrusion), these salts are released and can cause patches of damp. However, the temporary moisture is just a trigger, not a root cause, the root cause being the salts - agin it is not a source of moisture, so can't cause mould, rot or any damage to the properties structure. You can read more about this here:
🔗 damp.ai/hygroscopic
Key Points to Address the Issue:
Replastering Isn’t the Solution if there iOS a source of moisture: Simply replastering won’t solve the underlying problem. These methods mask the issue rather than fix it and can trap moisture, risking rot, making things considerably worse. The trouble comes if there is an actual source of moisture, be that condensation or leak, the damp proofing makes it worse.
Condensation in the Flue: You’re right that moisture can condense inside the flue, typically because the flue is thinner than then main external wall. This can be mistaken for rising damp, leading to unnecessary and damaging treatments.
Breathable Materials: Using breathable paints and materials like lime plaster allows moisture to move freely in and out of the walls. Vinyl paints and modern materials trap moisture and lead to ongoing problems. 🎨🧱
Avoid Damp-Proofing Injections: Injecting damp-proofing chemicals into walls, especially with lime pointing can be disastrous. It damages the wall, traps moisture, damages the breathability of the structure, will always look unsightly and is extremely difficult to undo.
A Practical Alternative for Hygroscopic Salts
By the way, while I recommend using an oil-based primer to cover hygroscopic salts, I recognise that this approach shares some similarities with what damp-proofers do. However, there are three key benefits:
Easily Removable: If hygroscopic salts are misdiagnosed and there is, in fact, a source of moisture, the primer can be removed without major disruption. 🛠️
Minimal Coverage: The primer only needs to be applied to small areas, not wall-to-ceiling, so it won’t significantly impact the breathability of the wall. 🧱💨
Cost-Effective: It works much better than damp-proofing at hiding hygroscopic salts, without the need for destructive work, and for a fraction of the price. 💰✅
A Holistic Approach:
Old houses need to be treated with respect for their original materials and design. When you stick to lime, breathable finishes, and proper ventilation, these buildings perform beautifully. Modern interventions often create more problems than they solve - as you said, it becomes an unhealthy situation for both the house and its occupants.
Thanks again for sharing your experience - the more we educate homeowners and professionals, the better we can protect these beautiful historic buildings! 🏛️✨
Best of luck with your work in conservation,
Simon
🌐 Try our AI tool: damp.ai - feedback is always welcome! 😊
This is all really good information for anyone who thinks they may have damp problems, thank you.
Thank you for your kind words! 😊 I’m glad you found the information helpful. It’s surprising how often hygroscopic salts are mistaken for rising damp, especially on upper floors like chimney breasts where rising damp can’t occur 🏠💧. Understanding these subtle differences can save a lot of unnecessary treatment and expense 💸. If you have any questions or specific damp issues you'd like advice on, feel free to use damp.ai - always trying to help solve the root cause of damp, not just the symptoms! 🤝
A good way to find this hygroscopic salt dampness on old chimney breast walls, is to humidify the room. Even boiling a kettle can make them show up. On property surveys we spend a bit of time looking for these areas, because even if they are visually unseen on the day of the survey, they always show up on a standard resistance type damp meter. Great videos as always & very informative, even to other surveyors.
Thanks for the great tip, Nigel! 🙌 Humidifying the room (or boiling a kettle ☕) is such a practical way to highlight those hygroscopic salt areas! 🔍 While some people call these walls "contaminated," I don't - they aren't a source of moisture 💧, mould 🦠, or rot 🍂. It's really just a feature of the salts.
Covering them up is simple! 🛠️ I usually recommend an oil-based primer 🖌️ because it's affordable 💷 and easy to apply. But any impermeable coating works, even insulation! 🏠
Thanks again for the kind words and for sharing your insight! 👍😊
@@dampsurveys the biggest issue with this type of chimney salt damp staining is that they look unsightly. You pay £100's of thousand buying a property, or you spend £1,000's on decoration, only for these patches to randomly appear & sometimes disappear. Is a very misunderstood phenomena that I see often. It confuses, surveyors, builders, architects & other professionals regularly.
Thanks, Nigel-what an insightful observation! 😊 I completely agree. Hygroscopic salts are often misunderstood, leading to unnecessary and expensive treatments. The rising damp industry has built an empire on this misunderstanding, costing the UK billions annually. If we could spread the word about what’s really happening with these salts, we could collectively save £2 billion a year. Please do help amplify the message!
What Are Hygroscopic Salts?
Hygroscopic salts are not a source of water themselves. They exist in a state of dynamic equilibrium, continuously absorbing moisture from the air when humidity is high and releasing it when humidity is low. This constant exchange creates visible damp stains that appear and disappear based on environmental conditions like temperature and humidity.
Why They’re Misleading:
1️⃣ Not Drying Water
Unlike water from leaks or condensation, the moisture associated with hygroscopic salts doesn’t behave in a predictable way. It’s linked to changes in the surrounding air and doesn’t leave a cooling thermal signature like actual drying water would.
2️⃣ Triggering Factors
Hygroscopic salts are often mistaken for signs of rising damp, but they are brought to the surface after damp events, such as:
🧪 Chimney removal or replastering.
🧪 Leaks or rainwater penetrating damp.
🧪 Intense condensation.
🧪 Damp-proofing treatments, where slurry is applied to slightly moist walls.
🧪 I’ve even seen cases where dry lining was installed using aqueous adhesive, causing the salts to activate and show through. Using an expanded foam adhesive would have avoided this issue entirely.
3️⃣ Unsightly but Harmless
While the stains are unsightly, they rarely indicate a structural issue. Treating the walls with oil-based primers, like Zinsser Cover Stain, is often more effective than removing the plaster entirely-especially if the underlying wall is already dry.
Managing Hygroscopic Salts
🔎 Step 1: Eliminate Moisture Triggers
Ensure there’s no ongoing source of moisture, such as:
🎨 Leaks in the chimney or roof.
🎨 Penetrating damp from rain.
🎨 Poor ventilation leading to condensation.
🔎 Step 2: Monitor and Confirm
Use data loggers to track humidity levels around the affected area and confirm the environment is dry before applying treatments.
🔎 Step 3: Treat the Aesthetic Issue
Apply Zinsser Cover Stain with a 300mm overlap to seal the visible stains. This approach avoids over-application, which can inhibit the wall’s breathability.
Suggested Videos:
1️⃣ "Hygroscopic Salts Triggered by Rain Part 1" - th-cam.com/video/HJR7MqbnRZ4/w-d-xo.html
2️⃣ "Hygroscopic Salts Triggered by Rain Part 2" - th-cam.com/video/cRVhGlNmT3I/w-d-xo.html
3️⃣ "Hygroscopic Salts Triggered by Rain Part 3" - th-cam.com/video/KykkQ4u_siE/w-d-xo.html
4️⃣ "Damp on Chimney Breast" - th-cam.com/video/LgkJcD5FTgc/w-d-xo.html
Let’s Spread the Word!
This is an incredibly misunderstood phenomenon that confuses surveyors, builders, architects, and more. But together, we can demystify damp. Visit damp.ai for more insights, and don’t forget to subscribe to my channel for daily videos addressing real-world issues like this. 🌟
📚 Coming Soon: My eBook this summer will cover these topics in greater depth, helping homeowners and professionals alike to make informed decisions. Stay tuned! 🚀