Weathering of building stone: Approaches to assessment, prediction and modelling

In the natural environment, weathering and breakdown of stone is an accepted part of long-term landscape development but the same acceptance of change and deterioration is not extended to stone used in construction especially when such deterioration affects historically and/or culturally important structures. The value of an integrative approach to improve understanding of weathering and failure of building stone is examined through review of three investigative approaches. First, condition assessment of the structure is an essential component of any remedial programme as this facilitates identification of the nature, extent and severity of deterioration and provides a measure of the degree of intervention required. Summary data are reported from a Staging System that seeks to impose a more formal structure on condition assessment providing a commonality of methodology, terminology and meaning whilst also providing a procedure for forecasting extent of treatment required and likely outcome in terms of ‘life expectancy’ of the structure. The second approach to investigation is assessment of the appropriateness of replacement stone. This involves many analytical procedures but gas permeametry in particular is becoming an increasingly useful portable, non-destructive analytical technique for predicting potential durability. Summary data are presented from analysis of Dumfries sandstone and Leinster granite illustrating spatial variability in stone surface permeability and the implications of this for post-emplacement weathering response and long-term durability. The final approach involves modelling potential stone decay pathways. The ability to more accurately model stone behaviour has significant implications for the design of conservation strategies and the avoidance of inappropriate treatments that may, inadvertently, trigger the sequence of