Two Looks Back to Move Forward. Today’s Evaluation of Opposite Approaches of Concrete Repair in Heritage Preservation

Two general approaches in concrete heritage preservation can be distinguished since the 1980s. Both have been met with approval from the official preservation authorities in German-speaking countries up to the present day. However, regarding the conservation of material substance and appearance, they are diametrically opposed and differ strongly regarding continuous reparability, reversibility, and monitoring. The following re-assessment is based on a historic analysis of the formation of the two approaches, which were for the first time widely discussed on the repair of the Antoniuskirche in Basel (repair 1987–1991) and the Liederhalle in Stuttgart (repair 1991–1993) respectively. The latter has been acknowledged as a best practice example for localized repair and careful preservation, whereas the first has been discussed as an exemplary case for renewal with imitation of the original surface appearance. However, as revealed trough a recent in situ condition survey and accompanied archival research, this one-sided perception has so far lacked to consider the diversity of the actual repairs. After about 30 years, we re-evaluated the two prominent cases of early concrete repair in heritage conservation to discuss the appropriateness and suitability of the approaches and their long-term consequences, also in light of the comprehensive contemporary discussions. Based on an ongoing DFG-funded research project, the paper points to new methods of systematic photographic survey and color measurement for the examination of repaired concrete surfaces, which are highly relevant for their assessment, monitoring and thus for future decision-making processes.