The portals on the brick building: Construction of St. Mary’s Church in Rostock began in the 13th century and the sacred brick Gothic building was completed in the middle of the 15th century. Two portals are made of limestone. They were restored between 2009 and 2011. The south and north portals of the large transept of St. Mary’s Church in Rostock are […]

The portals on the brick building: Construction of St. Mary’s Church in Rostock began in the 13th century and the sacred brick Gothic building was completed in the middle of the 15th century. Two portals are made of limestone. They were restored between 2009 and 2011. In contrast to the other portals and window pinnacles, the south and north portals of the large transept of St. Mary’s Church in Rostock are made of Gotland limestone. The north portal is made of light beige crinoid limestone with gypsum backfill mortar, while the south portal is made of gray-blue peloidal limestone with backfill mortar based on swamp lime. This makes them a special feature compared to the otherwise continuous brick construction and emphasizes the building’s characteristic transept.

The portals, which are cut deep into the structure, are divided by pilaster strips and archivolts. The north portal also features ornamental floral decoration. Additions and adaptations used in connection with the assembly are clearly visible. Bricks embedded in plaster mortar complete the portal. As the pointed arch portals were installed as a second use, it can be assumed that, due to their quality, they were removed from the previous building and later reassembled in the transept. This is reflected in the north portal by the different stone materials of the inner wall and the outer archivolts. The strong joints at the south portal. The limestone portals superficially showed a cementitious, obscuring reworking of the heavily damaged natural stone surfaces. This layer was characterized by cracks, was hollow in places and showed flaking and spalling. The physical properties of the extremely hard reworking layer and the building-damaging chlorides and nitrates embedded in it led to the decision to remove this layer.

Damage caused by salt and acid formation due to the permanent build-up of moisture was noticeable underneath. This led to structural destruction and fissuring. The damage is caused by the absorption of water from the soil and air. The water transports various chemical compounds and these are deposited on the surface or in the resulting cavities. Existing salts originate from deposits such as dirt (soot, grease, bird droppings, microorganisms, etc.) and building materials containing cement. The former “protective sludge” also causes subsequent damage to the original substance from top to bottom. The north portal mainly showed a strongly softened, sanding surface, while the south portal showed flaking, shell-shaped surface lifting combined with cavities. The restorers removed the cement slurry from the limestone in order to reduce the potential for damage to the natural stone surfaces and thus preserve the underlying limestone in the long term. They treated this slurry dry using the low-pressure particle blasting method. They manually thinned out any remaining residue. Depending on the size and layer thickness, they used compressed air and compressed air micro-chisels or the low-pressure blasting method to restore open-pored surfaces. Grout containing cement mortar, putty and rusting iron parts were removed. Due to the different types of stone on both portals, suitable supplementary materials were developed in the laboratory and later tested in test areas on site.

Read more about the restorers’ approach to the restoration of the limestone portals of St. Mary’s Church in Rostock in STEIN in February 2014.

Pictures: Hans Leisen, Marcus Mannewitz and Boris Frohberg

Too little space and inadequate storage conditions: RESTAURO spoke to specialist restoration planner Johannes Baur from Munich about sustainability and the sensible use of technology in museum depots Johannes Baur has not only been advising cultural institutions for a good twenty years, but has also been realizing museum depots and archives – and doing so internationally. The fact that there was an urgent need here came to the attention of […]

Too little space and inadequate storage conditions: Restauro spoke to specialist conservation planner Johannes Baur from Munich about sustainability and the sensible use of technology in museum depots

Johannes Baur has not only been advising cultural institutions for over twenty years, but also realizes museum depots and archives – internationally. The specialist conservation planner from Munich, who has his own office, noticed that there was an urgent need for this as early as the mid-1990s while working as a furniture restorer at the Munich City Museum.

Planning projects run in parallel

Museums were complaining about a lack of space and inadequate storage conditions in their depots. At that time, Johannes Baur was responsible for setting up an external depot, among other things. Today, his clients include the Prussian Cultural Heritage Foundation (Berlin), for whom he provided advice and specialist planning for the museum depot in the new building of the Museum of the 20th Century at the Kulturforum (Herzog & de Meuron). Johannes Baur is also involved in the extension of the Kunsthaus Zurich (Chipperfield Architects). In addition to these two major projects, the expert has numerous others running in parallel. Two permanent architects are now part of the team. Johannes Baur had already converted the office completely to digital before coronavirus and invested heavily in technology. Nothing works without CAD programs anymore. “We are in constant contact with other planners to coordinate the different plans,” reports Johannes Baur. “The projects are in the cloud, so we can access them from anywhere at any time. The lockdown was therefore not an issue. We communicated via video conference and moved the plans back and forth.”

Expertise in warehouse technology

Customers come via recommendations and tenders. But the revamped website also attracts a lot of attention. “When it comes to depot planning, we offer all service phases from one to nine (according to HOAI). And we have a great deal of expertise, including in storage technology.” One challenge that is often underestimated is structural engineering, which must be addressed at an early stage, says Johannes Baur. “We often only get involved in service phase three or even five. However, the earlier we are involved, the better.”

Johannes Baur recommends planning conservatively

Baur attaches great importance to sustainability when planning depots and archives. “Energy requirements and the costs of energy and building maintenance now exceed the acquisition budgets of museums. I therefore always suggest planning conservatively, especially when building depots. In contrast to permanent exhibitions, which are replaced every ten years at the latest, not much changes here, so for me the planning approach is 50 years plus.”

Focus on low tech

Johannes Baur generally relies on low tech. He is reluctant to install electric travel systems, for example. “Up to certain loads, a system with handwheel operation will still be working perfectly in twenty or thirty years’ time. However, you need to be involved relatively early on in the project phase, as otherwise high rooms may be planned. And that’s where large travel systems become necessary, which in turn can no longer be operated manually once they reach a certain size. So technology wherever it makes sense.” We often receive inquiries about what needs to be considered. “As with architects, our work is divided into an advisory area and a planning area. We often take on the role of mediator. Of course, we know the language of restorers, but also that of structural engineers and architects. And there are always challenges in communication.”

In the Collection Center: workplaces for conservators

Incidentally, Johannes Baur doesn’t really like to use the term depot or central depot. “I now prefer the term collection center. Because this is where work should be actively carried out – and, depending on the situation and space requirements, workstations for conservators should also be created. And we can also take really interested visitors there. In addition, there can be a meaningful link to museum education, for example.”

Reading tip: How to plan, build and use a depot or archive in a needs-based, environmentally friendly and sustainable way is shown in the newly published “Handbuch Depots und Archive – Handlungsempfehlungen für Planung und Betrieb”, edited by Dr. Kristina Holl and Prof. Dr. Ralf Kilian. Graduate conservator Katharina Haider wrote a review of the new publication for RESTAURO (8/2022). This covers the conception, planning and use of depots and archives, includes new buildings and conversions and is just as committed to sustainability, climate protection and energy efficiency as it is to preventive conservation.