Environmentally-induced stone decay: the cumulative effects of crystallization–hydration cycles on a Lincolnshire oopelsparite limestone

An investigation has been undertaken at St Andrew’s church, Walpole St Andrew, Norfolk, to establish the underlying causes of the observed stone decay to the upper parts of the six stone piers. The stone decay was first recorded in the early 1930s. The salt-contaminated masonry within the church has been shown to undergo severe salt decay during the summer, with little damage occurring over the winter months. The south aisle piers have been shown to decay 2.5 times faster than the north aisle piers. Although crystallization–hydration cycles have been identified, the rate of decay is at its greatest when the cycling is relatively infrequent. This was not the expected trend. Furthermore, it has been shown that during extended periods where the ambient relative humidity is less than 75%, the rate of decay reaches a maximum. It is the length of this ‘drying’ period that apparently has the greatest influence on the rate of decay and could explain the significant difference in the rate of decay between the south and north aisle piers. The results have serious implications for passive conservation, where it is often recommended to lower the ambient relative humidity to well below the equilibrium relative humidity of the salt contaminant, to avoid crystallization–hydration cycles. Since, at the time of building, the church was situated on the coast, it is possible that the sodium chloride contamination occurred during the building process (1440–1520), particularly since the area was prone to sea-flooding at this time. Alternatively, the salt could have been applied as a treatment during the general restoration of 1897. Whatever the source of the salt, it seems likely that the ambient environment was changed by the insertion of a sealed floor in 1897, which could account for the onset of the salt decay.     

Learning More About Learning Improves Teacher Effectiveness

The present study examines the possibility that teacher knowledge about learning may have an impact on the effectiveness of a school. Thirty-two secondary qualified teachers engaged in a professional development program that provided a framework for reflective study of the learning process, analysis of key aspects of learning in their classes, and identification of the implications for teaching. Changes in teacher effectiveness were monitored in several ways: (1) changes in the display of effective teacher behaviours consistent with a social-constructivist model of learning, (2) changes in perceived ability to facilitate learning in classes, and (3) changes in student performance. The findings support the prediction that involvement in a systematic exploration of the learning process, with teachers explicating their knowledge of learning, has an direct impact, on the display of effective teaching behaviours and on teachers' personal explicit theory of learning.