This case study is interesting in that the client had a damp proofing company say the issue was rising damp and recommended expensive damaging chemical treatment. Indeed the lower wall did look very damp, but the elephant in the room was mould and lots of it.
The client followed our recommended remedial actions and sold the property for a premium, see before and after photos.
Inside the hexagonal reception, we see mould. Mould only grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficiently ventilation. Ventilation is most effective when air is extracted at the source of humidity; bathroom, kitchen, drying clothes and occupied rooms. A secondary cause of excess humidity is low temperature. The hexagonal ceiling is not receiving warm air or there is heat loss.
There is a kitchen extractor fan, but it is not always used. Warm humid air is moving to the cold unheated hexagonal reception.
Mould and condensation forms dark dribble marks on the wall. The angled window ledge loses heat as it nears the cold outside, resulting in increased relative humidity, and risk of mould and condensation.
The bedroom is open plan to the kitchen and bathroom.
Condensation marks can be seen dribbling away from the single pain stain glass window.
We tested with a Protimeter damp meter in conductance mode. Damp meters measure electrical conductance. Water is a poor electrical conductor. It is salts in water that conduct electricity. Despite criticism, damp meters are a good test of dryness. Protimeter readings below 20WME are considered dry. At the time of the survey the wall was dry at 13WME, despite the recent rain. This demonstrates that the root cause is not penetrating damp, but condensation.
Dampness and mould is most visible in the bathroom, despite the bathroom having no external walls. I understand the condensing dryer is a recent purchase and that previously clothes were dried on radiators.
The bathroom is the root cause of most of the excess humidity. The extractor fan no longer works.
Controlling humidity is only effective when vapour from the source of humidity is isolated and extracting. Here we see a Door Doorway Gym Exercise Bar stops the bathroom door from being closed. The laundry room door is left open. Most of the mould and condensation will stop if a new extractor fan is installed, with a 30 minute overrun and the door is kept closed.
There are calcium sulphate salts on internal walls. These salts come from the building fabric, which dissolve in condensation, then diffuse and concentrate on the evaporating surface. They are benign, normally surface deep and will stop moving once humidity is back under control.
The dampness in this lower ground floor church conversion was not caused by rising damp, as incorrectly diagnoses by a damp proofing company. It was caused by excess humidity.
After following our recommendations.