An investigation into the non-uniform decay of Hardwick Stone

Hardwick stone as used on the vernacular Hardwick Estate buildings decays in a non-uniform way. Typically stones at Hardwick decay cavernously leaving the mortar matrix behind. Levels of decay can vary dramatically from stone to stone with one stone showing advanced decay whilst adjoining stones are relatively intact. Ten sample buildings giving a total of 1587m² of elevations and with a good geographical spread across the estate were surveyed. Ratings were assigned according to condition. It was shown with 95% confidence that the weathering on the western elevations is significantly worse than that seen on the eastern elevations of the sample buildings. Northern elevations had high levels of stonework in good condition, while western elevations had the lowest. The prevailing wind direction on the Estate is west to north-west. The difference in levels of decay below 1 metre and above 1 metre has been shown to be significant at the 95% confidence level with a slight correlation between levels of stone decay and building height (above sea level). The survey also highlighted stone decay parallel to, but offset from, the roofline where there were no overhanging gables present. In contrast, buildings constructed with protruding cills were often observed to have areas of decay underneath the cills. Stone decay often appears to be associated with the path of the chimney.