Damp on chimney breast of Victorian end terrace house
I have had two large isolated circular patches of damp on my chimney breast. My renderer can’t see any cracks in the outside wall so has removed the plaster to see if it dries out on the inside. I have been using a damp meter for the past 4 weeks but am consistently getting a reading if 17 in one small area – this doesn’t change with heavy rain. My chimney was taken down and sealed some years ago due to damp in my loft which now seems dry. Ventilation was put in and a chimney sweep said ventilation is good so I don’t think that is the cause. Grateful for your advice!
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Answer:
Based on the information provided, there could be a few potential causes for the damp patches on your chimney breast:
- Penetrating damp: Even without visible cracks from the outside, moisture can penetrate through porous bricks or mortar over time, especially in an old Victorian property. This could be causing the damp patches internally.
- Rising damp: If there are no issues with the roof or chimney, the dampness could be coming up from the ground through capillary action in the brickwork. This is especially common in older properties without proper damp-proof courses installed.
- Condensation: Poor ventilation or insulation can lead to moisture condensing on cold surfaces like chimneybreasts. However, you mentioned having good ventilation, so this may be less likely.
Here are some suggestions:
- Continue monitoring the damp patches with the meter after removing plaster to see if they dry out over time. This will help identify if it’s penetrating or rising damp.
- Get a damp specialist to do an invasive damp survey and analysis. They can better pinpoint the source with specialized equipment.
- Check the external ground levels and any damp proof course/membranes that may need repairing or installing if rising damp is suspected.
- Improve ventilation further if condensation is still a possibility after other causes are ruled out.
- As a last resort, damp proofing injections or a damp proof membrane may be needed if the source cannot be eliminated otherwise.
Persistent damp can lead to structural issues, so getting professional evaluation is recommended to identify and properly address the root cause in your Victorian home.
