The Globigerina Limestone of the Maltese Islands, widely used in construction and for restoration purposes, comes in a variety of types, with the Franka and Soll types (local terms) being the end members. The Soll type manifests widespread and often serious problems of durability and weathering resistance. The Franka type tends to be more durable. The selection of these materials is generally entrusted to quarry workers and builders, who primarily use visual criteria. This can lead to unsuitable stone being used. The current study uses ultrasonic and thermographic methods to distinguish between the two types at the extreme ends of the range, and to determine how their water absorption characteristics (fundamental when durability is being considered) can be evaluated. Results show that the Franka and Soll types behave very differently; ultrasonic testing showed that the Franka type possesses a significantly higher velocity compared with the Soll type; the thermographic technique verified that the Soll type absorbs less water by capillarity. Having an objective test to distinguish between stone types can lead to fewer errors in the choice of stone; such errors at present are possible because of the subjectivity of the methods used, with ensuing grave economic and practical consequences.

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