In-situ visual analysis and practical sampling of historic mortars

The practical aspects of sampling of historic mortars are dependent on external factors, such as conservation philosophy, which can constrain sampling activity, and/or laboratory analysis, which offer the answers to questions posed by an investigation. However, the utility of conclusions reached depends on the quality, and the relevance, of the samples taken for answering these questions. Two major controls operate on sampling practice; the objectives of an investigation and the analyses (physical, chemical or descriptive) needed to fulfil the objectives. A clear statement of the problems being investigated is needed and the full context of the investigation must be outlined before samples are taken. This can be achieved by structured recording of building characteristics, including the construction history of the building or "stratigraphy", decay states and the materials used. Visual analysis is a powerful and cost effective method of investigating problems, material variations and for selecting locations for sampling, if suitably experienced personnel are employed. Hypotheses can be formulated as to the cause of damage or the academic subject under study. Then specific sampling targets can be identified with knowledge of the variability of the materials available and the hypotheses to be tested. Laboratory and field analyses use a variety of instrumental techniques that each have minimum sampling requirements. The problems to be accommodated in standardising sampling practice include access to structures, acceptance of those trusted with sampling and the variability of reasons for sampling.