Linking the exposure conditions of defective blocks with expansion in an Irish home by monitoring and microstructural analysis

County Donegal is the epicentre of Ireland’s crumbling‑concrete‑blocks crisis, with thousands of homes exhibiting severe cracking, loss of strength, and reduced structural integrity within 10–15 years of construction. The damage was initially attributed to high mica content, which was thought to increase vulnerability to freeze–thaw deterioration. However, recent research has demonstrated that internal sulphate attack (ISA) is the primary cause of the observed degradation in defective Donegal homes. This study aims to document the exposure conditions and expansive behaviour of concrete blocks in the outer and inner leaf walls, as well as the rising wall, below ground level and an internal partition wall of a home that was confirmed to be defective as part of the Irish Government grant scheme to repair homes. To characterise field conditions and expansion, manual and automatic in-situ expansion, temperature and relative humidity monitoring was performed since January 2024 at selected locations within the inner and outer leaf walls and an interior partition wall. During the same period, temperature and relative humidity (R.H.) sensors, together with fibre‑optic vibrating‑wire gauges (VWG), were installed in both leaf walls and at a selected location in the rising wall to enable automated monitoring of expansion with temperature and RH. The findings rule out freeze–thaw as a potential deterioration mechanism in the home, as expansion was recorded during warmer months, and outdoor temperatures remained well above 0 °C throughout the winter of 2024. Microstructural (SEM/EDS) analysis confirms ISA in the blocks of the inner, outer, and rising walls. Results also indicate the potential for further expansion at least in the rising wall. Monitoring will continue for approximately one more year to further capture the exposure conditions and ongoing expansive behaviour.