- Client
- Appointed by PDP Green
- Services
- Building Pathology · Environmental Monitoring
- Period
- 2015 – 2019 (interim assessment)
A complex combination of causes.
SMT Associates was appointed by PDP Green to investigate damp conditions within the Earl's Chamber at Chepstow Castle and subsequently monitor the effectiveness of remedial works. Our investigations and monitoring extended from 2015 to the interim assessment in May 2019.
The unoccupied chamber presented a complex combination of cold masonry, high humidity, salt contamination and localised water penetration. Initial environmental monitoring recorded an average internal temperature of approximately 5°C and relative humidity of 96%, leaving the chamber highly vulnerable to condensation on cold surfaces.
Understanding the causes
Our assessment combined visual inspection, repeat moisture-meter surveys, thermal imaging and environmental data logging. Monitoring included the room environment and probes installed within the masonry, allowing conditions to be assessed over time.
Interpreting the evidence required particular care. Salts in plaster and mortar can produce elevated electrical moisture-meter readings, so readings from masonry were treated as comparative indicators rather than direct measurements of its moisture content. Visible wet joints, surface temperatures, environmental conditions and changes in timber moisture were considered together.
Tracking the building's response
Following remedial works and commissioning of the air-handling system in January 2018, repeat inspections demonstrated progressive improvement. Thermal imaging showed that the masonry surfaces had warmed, while environmental monitoring recorded substantially lower relative humidity.
By the May 2019 assessment, average temperatures at the two internal monitoring positions were approximately 20–21°C, with average relative humidities of 40% and 52%. Floorboard moisture readings had reduced from approximately 14–27% in 2015 to 7–12%. Previously wet mortar joints also showed visible improvement.
These findings supported the conclusion that the fabric was drying and the risk of surface condensation had substantially reduced under the monitored conditions.
Evidence to guide conservation
The interim assessment recognised that drying massive masonry walls takes time. Continued monitoring and limited gravimetric sampling were recommended to confirm the remaining moisture within the masonry and distinguish it from the effects of salt contamination.
The project demonstrates how building pathology can support historic-building conservation: identifying interacting causes, interpreting measurements in context and checking the effectiveness of remedial work over time.