Building stone has a finite life that can be drastically curtailed when it is placed in the often-aggressive environments experienced in today's urban settings - yet stone masonry is still widely recognized as an adaptable and sustainable construction material, with a low carbon signature, and as a repository of much of the world's tangible cultural heritage. Arising from this, it is essential that the choice of new and replacement stone and the conservation of decaying stone is underpinned by a detailed knowledge of how different stone types decay in specific environments and what factors trigger decay and control its rate once it is initiated. Data are limited from the wide range of stone types seen in structures existing today - the performance characteristics of only a limited number of comparatively durable stones are known and these are largely resistant to physical damage and decay is driven primarily by dissolution. The rate of solution of stones is influenced by factors such as rainfall amount, timing, atmospheric conditions and chemistry and thus, with knowledge of micro-environmental conditions in and around the building stone, decay rates are largely predictable from short-term observation. Despite rather advanced non-destructive methods currently used for assessing the deterioration process and their rates, the fate and extent of inner contamination of building materials remains largely unaccounted for by such methods. Therefore qualitative online health monitoring of these building materials using embedded sensors is essential, not only from the standpoint of economic planning and maintenance, but also on cultural, technical and scientific grounds. Novel sensor systems designed specifically for use in buildings constructed from stone can provide the data that conservators need which enable them to understand better the complex processes that are on-going and to model better and thus plan repair and maintenance procedures in a cost efficient and timely way. This work builds upon several previous EPSRC grants into both fibre optic sensor systems, civil structural monitoring and heritage stonework. However in particular this follow on application builds upon the successful technical achievements of a grant focusing on the test, evaluation and design of a suite of new sensor systems for stonework monitoring for both moisture and chloride transport. The work enabled a more detailed evaluation of the decay processes and the beginning of a better understanding of several key applications-focused issues from that grant funded. Recognizing that the Follow-on Fund is concerned with development towards an identified commercial opportunity, this project can be summarized as the development, commercialization and marketing of fibre optic sensor systems for monitoring ingress of moisture and moisture-borne salts in the context of structural monitoring and decay prevention of stonework, both historic and modern. Through carefully considered technical and commercial plans, it is intended to refine the sensors for the specific monitoring environments of stone masonry strucures and develop probes which can be used in stonework in a minimal invasive manner. The commercial feasibility will be established through in situ evaluation, market testing and working closely with an SME with specialised knowledge in monitoring the built environment.