Sandstone was always widespread used in large scale building works in the past centuries, for its abundance and easy carving nature, however this latter also meant lower resistance to the elements and to air pollution with the start of the industrial revolution. Conservation work on historic buildings (stonework, mortar) is often hindered, if not prohibited, by not knowing the composition and sources of the materials used for their construction. Standard test methods are not relevant or not practical in most of the cases simply by not been developed with the peculiarities of historical samples in mind, i.e. these do not consider the difficulties with small sampling sizes, limited chances to repeat a measurement, or the preference of non-destructive assessments. Modern laboratory techniques, however, can be instrumental for providing the required pieces of information, even with minimal or no salvaging of the precious original samples. Adopting such specific assessment methods (CT scanning, X-Ray Fluorescence spectroscopy, X-Ray Diffraction and Mercury Intrusion Porosimetry etc.) will enable selecting the correct proxy materials, which are identical with the originals and therefore comply with the guidelines of the Venice Charter for the Conservation and Restoration of Monuments and Sites. Successful application of such sophisticated laboratory characterisation work is presented in case studies involving Kelso abbey and Glenfinnan viaduct in Scotland.