Damp around internal air vent on blocked up fireplace

It sounds like you're dealing with a challenging situation regarding dampness around the internal air vent of your blocked-up fireplace. Here are some considerations and steps you might take to address the issue: 1. **Assess the Cause**: Damp patches appearing at the corners of the air vent could be due to various factors, including moisture seeping through the bricks or breeze blocks, inadequate ventilation, or water ingress from the chimney area. It's essential to accurately diagnose the root cause before proceeding with any repairs. 2. **Review Construction Materials**: Breeze blocks are typically more porous than bricks and may be more prone to allowing moisture penetration. However, both bricks and breeze blocks can be used for fireplace infill, but proper sealing and damp-proofing measures should be implemented to prevent moisture issues. 3. **Evaluate Ventilation**: Poor ventilation can contribute to damp problems, especially in enclosed spaces like blocked-up fireplaces. Ensure that there is adequate airflow around the air vent area to allow moisture to dissipate. Installing a vent cover with mesh can help prevent debris and pests while still allowing airflow. 4. **Consider Damp Proofing**: If moisture continues to be an issue, it may be necessary to implement damp-proofing measures. This could involve applying a damp-proof membrane or sealant to the affected area to prevent moisture ingress. Additionally, re-plastering with a waterproof or damp-proof plaster can help mitigate future dampness. 5. **Professional Assessment**: Given the complexity of the issue and the potential need for structural repairs, it may be beneficial to consult with a qualified building surveyor or damp-proofing specialist. They can conduct a thorough assessment of the problem and recommend appropriate solutions tailored to your specific situation. 6. **Historical Considerations**: The age of your home and the construction materials used may present unique challenges when addressing damp issues. It's essential to consider the historical context of the property and any preservation requirements when planning repairs or renovations. 7. **Regular Maintenance**: Once repairs and damp-proofing measures are implemented, ongoing maintenance is crucial to prevent future damp problems. Regularly inspecting the area for signs of moisture and addressing any issues promptly can help preserve the integrity of your home. By taking a systematic approach to address the dampness around your fireplace air vent, you can effectively mitigate the issue and ensure a dry and comfortable living environment. If you're unsure about the best course of action, don't hesitate to seek professional guidance from experts in the field of building preservation and damp-proofing.

Chimney breasts were the original damp proofing systems, houses were built to have mild draft also, these combined kept damp under control. Fast forward to today, the same properties have double glazing, central heating, increased occupancy (conversion into flats) has inadvertently created secondary issues like condensation etc. Coal is mined and is a sedimentary rock, it also has chlorides and nitrates which over time saturate chimney breasts and the salts migrate. This would need to be surveyed and a specification of remedial treatment outlined by an expert, please do not disturb the bitumen as it may be harmful and would need to be tested!

I have been out to these problems in the past, the most likely issue will be not chimney elephants foot installed. This will Still allow air down the chimney to keep ventilation but these stop water penetration and water running down. The water will be sitting on the concrete harth and starting creep into the blocks or when it’s coming down the chimney it’s hitting the vent area