In most cases the naturally or anthropogenically induced weathering creates only a weathering zone at the building stone. This is located on the object surface and reaches a material depth of a few millimeters or centimeters.
In relation to the architectural body, the loss or damage of the weathering zone is to be described as marginal. However, from a conservation point of view, the loss of the surface is to be regarded as extremely serious. The object surface contains a wealth of information about what constitutes the cultural value of the historical object: its surface treatment, design, setting and deco- ration, that is, its human-made texture.
Only a few non-destructive, or destructive, measuring methods are available for the investigation of this delicate range. These in
clude the measurement of cohesion by means of ultrasonic velocity and the surface hardness.
Stone conservation would also have to deal with a further, methodically problem: Tests for the evaluation of suitable stone consolidants are usually carried out by testing series of fresh rock material. The results from these test series are then transferred to the application at the object. In this case, it is ruled out that weathered rock has entirely different properties than quarry fresh material.
In this ACS-study, the test bodies used were artificially aged in different ways. The aim was to produce as similar as possible weathering forms to the test bodies as they are observed on the outdoor objects. The artificial alteration took place by salt crystallization, by heat applied on one side and by ice crystallization. The applied methods of aging are presented and the effect of artificial weathering is reproduced with the above methods. In addition, the artificially altered test bodies were investigated by the measurement of porosity, water absorption and thin sections, and were compared with the weathering characteristics found on the historical objects, three sandstone steles. After solidification with silicic acid esters, the test bodies and the objects were subjected to the same examination procedure and the results were compared comparatively. The results show the possibilities and limitations of the assessment of stone consolidation measures on objects made of sandstone and open up new perspectives for a realistic examination of the evaluation of the consolidation effect on test bodies and historical objects in situ.
The study performed by Wedekind, Schmidt and Fischer will be presented on the 26th of January at a International Conference of the HAWK (University of Applied Sciences and Arts) in Hildesheim. The international conference will take place on the occasion of the 30th anniversary of the study-courses of conservation / restoration at the HAWK. From 25 to 27 January 2018 in Hildesheim, experts and interested parties will find together under the title "Consolidation and Communication". What is new about the HAWK conference topic is that it does not want to concentrate on the consolidation of a special material area, as is customary, but explicitly wants to intensify the communication between the different material areas in conservation and restoration. Experts from Germany, Great Britain, Italy, Austria, Switzerland, the Czech Republic and Malta will present experiences and studies.