Developing a Robust, low-cost Exposure Trial Methodology for Monitoring the Deterioration of Earthen Material

Exposure trials have long been used as an approach to assess changes in natural and building materials when exposed to outdoor conditions. They involve placing replicated, well-characterised material samples in monitored environments to observe, measure, and quantify their changes over time. To date, they have predominantly been undertaken on stone materials and have rarely been used to assess change in earthen materials used in built cultural heritage, even though deterioration of earthen materials can occur over time periods commonly used in exposure trials. The implementation of exposure trials can be limited by practical, methodological and cost challenges. A robust and replicable methodology that uses widely available and relatively low-cost equipment is required to optimise their use in earthen heritage research. We used a range of laboratory and in situ tests at six field sites located on three continents to develop a robust, low-cost exposure trial methodology for earthen materials. We developed an easily replicable and standardised test rack design holding samples in specially developed acrylic sample holders; methodologies for capturing change to the samples, such as using a semi-quantitative visual assessment method and photogrammetry, were tested and standardised; and a standardised approach to digital data storage was constructed. While extensive planning and pilot studies are essential for developing robust methodologies that are repeatable across sites, this can take longer than anticipated due to practicalities of working internationally. Nevertheless, time invested in planning successfully resulted in a robust, low-cost exposure trial methodology for earthen heritage that can be implemented at sites globally.