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The main reason for undertaking the renovations is that the building was leaning from the vertical axis. The leaning has reached up to 460 mm maximum deviation of the tower wall from the vertical axis, and has been caused by insufficient load-bearing capacity of the ground on which the whole church is built. According to static calculations, the ground’s load-bearing capacity has been exceeded by up to 2.7 times. This has led to the sinking of the foundation structures – the pillars – 150 to 200 mm. Therefore, the building is leaning because the weight of the towers has shifted the center of gravity of the structure to the west. J. B. Santini tried to solve this problem, too, by adding a vestibule. Another major problem of the building was the dampness of the structures caused by the missing damp-proofing of the load-bearing walls and the floor, as well as by moisture condensation due to frost penetrating the flat terrace roofs.
During this time, important preparations were underway – exploratory bore holes in both the interior and the exterior, and also negotiations regarding planning, scheduling, sequence of projects, and financing of the complete and complex renovations. It was decided to finance the whole construction from our own resources – that is, from the income from tourism, without subsidies, grants, and funds. We made this decision because it gave us a certain kind of freedom to conduct the renovations “our own way”, without unnecessary paperwork and tenders, and with suppliers of our own choosing. Further, we needed to approach the design and realization teams and agree on long-term coopera-tion. Ing. Vít Mlázovský was named the chief project designer and Lanostav s. r. o. became the general contracting company.
The renovation of the terraces (2015-2016) included covering them by a temporary roof and com-pletely removing all the layers, down to the reverse side of the stone vault. The vault was recon-structed and structurally secured by pull pins, and the damaged parts of the masonry were redone, together with the perimeter wall. At the same time, the plinth section of the church was restored, and a drain was fitted in the newly built underpinning. The drain is covered by a lead-lined trough which allows the terrace to be drained by vents in the wall. All this was covered by a drainage layer of aggregate and sand, in which sandstone pavement was embedded. This new composition of the terraces has eliminated the condensation caused by frost penetration and, moreover, it has allowed us to open the terraces to the public. The impetus to renovations of the hanging decorations in the interior of the lower chapel was the fall of one of the pendants made of thigh bones. Subsequent research confirmed our concern: the an-choring components and steel wires had rusted to the point of starting to fail. It was a ticking bomb waiting to explode. The Parish and restorer Tomáš Král prepared a schedule of repairs and still in the same year (2015), the most seriously damaged components started to be restored. The restoration process is as follows: detailed photo-documentation is conducted prior to taking down the pendant, individual parts are labeled, and the pendant is removed, packed, and sent to the restorer’s work-shop. In the workshop, each pendant is blow-cleaned by pressurized air, taken apart, and each part is mechanically cleaned by nylon brushes, disinfected, and stabilized in lime water. Then the individ-ual parts are fastened to new anchoring components, and the old anchor pins in the walls are re-placed by new, stainless steel ones. The whole process is done in a way that will make dismantling the pendants in the future easier. In the final step, the pendants are fastened to the prepared an-chors. Complicating the work, because the chapel continues to be open to visitors, the restoration must be carried out after closing time, in the evening and at night. Moreover, dismantling too many pendants at once would leave nothing for the visitors to see. In 2016, after the most seriously damaged pendants were repaired, we decided to restore the chan-delier. During the dismantling of the chandelier, we discovered that the chandelier’s anchor was only wedged in the vault by a no-longer-functional oak wedge and a piece of lead. The chandelier is com-posed of a wooden vertical stem, four circular storeys, and cradling supported by wrought-iron strips. The surface of this wooden frame is covered in bone decorations fastened to the frame with spikes and screws. The width of the chandelier frame is 1,915 mm, the height of the frame is 2,086 mm, and the total weight of the chandelier is approximately 150 kg. There are 1,041 bones in the chandelier decorations.
In 2017 and 2018, damp-proofing of the Ossuary masonry was done by creating drainage and venti-lation channels around the perimeter of the whole building. We also started to repair the façade of the lower chapel of the Ossuary. The exposed perimeter masonry, mostly made of stone, was recon-structed, including filling in of the joints with mortar, re-masoning and repairing the load-bearing pillars, and finishing the openings of the Baroque windows. The windows were removed and refur-bished, together with restoring the stained glass, and then they were re-fitted into the prepared openings. Damp-proofing construction work, which exposed the Ossuary foundations down to the level of the footing base (2,5-3 m), were preceded by rescue archaeological research. During this research, all deposits and all evidence of burials were removed within a 2-metre belt along the whole perimeter of the Ossuary. This represents the largest sample of its kind that has been examined in Europe; the findings contain information about the Mediaeval population that occupied Kutná Hora and the sur-rounding area. The uncovering of the cemetery brought several surprises. It was originally presup-posed that burials next to the church did not begin until after the church was built. However, several tens of graves were disturbed during the church construction, which means that the graves were older than the church. Before the Ossuary was built, an older structure stood nearby. Corner rem-nants and one wall of this structure were also found. The rest of this structure lies under the current cemetery and is not open for research. Rescue archaeological research at the Ossuary was started on 30 May, 2016, and continued until 16 August, 2018 (from the originally planned four months it was extended to 2 years and three months). The number of excavated skeletons was 1,817, and 32 mass graves were discovered. One part of the mass graves was dug in 1318 for victims of the Great Famine, and the other for victims of the Plague in 1348-1350. Some of the mass graves disturb each other, and so we can unequivocally date four of them to 1318 and another seven to 1348-1350. In 2018, some of the renovations moved into the interior of the Ossuary, where a working space for restoring the bone pyramid was created. A temporary entrance was made in the northern Gothic window and a wooden structure with a staircase was built, which enabled construction work and transportation of bone remains to proceed. The preparations for the interior renovation included assembling a temporary dust-proof wooden partition with a photo mural and “viewing windows” to minimize the impact of the work in progress on the visitors’ experience of the Ossuary tour and to offer the visitors some satisfaction.
The dismantling of the pyramid was started in January 2019 by taking apart the polychrome wooden crown. First, the pyramid was fully documented, photographed and mapped. The dismantling of the pyramid was done storey by storey, from January 2019 to the end of March 2019. The bones were put in carton boxes and taken to the restorer’s workshop. Altogether, 1,500 boxes were filled with bones. Inside the pyramid, there were 6 cubic meters of construction debris which smoothed out the unevenness and helped to strengthen the pyramid. From April 2019 to October 2019, the bones were cleaned and preserved in the restorer’s workshop. Various cleaning options were tested, including, for example, washers, but in the end the bones were washed manually, with water under gentle pressure and using nylon brushes. Then the bones were disinfected and stabilized in lime water, and dried by large blowers hanging above the multi-tier racks. After drying, the bones were placed back into boxes and prepared for transportation to the Ossuary. The process of reassembling the pyramid is now under intensive consideration, with the goal to start putting the pyramid back together in the winter of 2020/2021. Under the pyramid, the floor was made of bricks, and around it, there are Santini’s original two-coloured (black-red) diamond-shaped floor tiles. The individual segments are composed into a complex geometric figure with the effect of a flower and also of cubes stacked on top of each other. During the whole of 2019, intensive work was done on the emerging space in the front part of the original trench, in the so-called “bookshop”. The development of this space had been approved ear-lier, when various possible ways of relieving the constantly overcrowded Ossuary entrance were be-ing examined. At that time, a trench was dug around the church for masonry rehabilitation. And, thanks to the unexpected discovery of an historical entrance into the lower chapel, the idea was conceived to use this entrance and connect the original lower chapel with a new addition which would house a souvenir shop, a small exposition, and facilities for guides. Architects Filip Kosek and Jan Říčný from the Prague architecture studio RCNKSK were asked to design the newly created space of the “bookshop”. The interior of this addition is supposed to evoke as much as possible the atmos-phere of being underground and to remind visitors that this place is a former graveyard. Therefore, it was agreed that the final coat of the interior perimeter walls would be done using the rammed earth technology. However, to date there is no one in the Czech Republic who would have experience with this technology, and so we approached Austrian expert Hanno Burtschner, and during the au-tumn months, earth ramming was tested right in the space of the emerging addition. Prior to this testing, the foundation for the addition’s perimeter wall was laid, and then a supporting wall made of permanent formwork blocks was built, including quality damp-proofing. The rammed earth tech-nology itself was applied using the same formwork that is used for concrete. The earth mixture is composed of soil, sand, fine and coarse gravel, clay, and an appropriate amount of water. The mixed materials are then poured into the formwork and rammed, either manually or by a pneumatic ham-mer. This process is repeated several times. After the formwork is removed and its imprint smoothed out, the wall dries out and gains its final compactness. The individual layers of the rammed materials form horizontal lines that have a strong aesthetic effect. The ramming of the wall at the Ossuary took five weeks (April 2020 – May 2020). Experts had to prepare 14 cubic meters of materials. The final length of the wall is 27 m and its height is 2.2 m, so altogether it covers approximately an area of 60 square meters. The wall was rammed in layers of 9 cm which were rammed down to 5 cm. The wall consists of 46 layers. In the summer of 2020, inten-sive work was also done on the ceiling of the addition which will be made of concrete but will be shaped into “bellies”. The moulds for these “bellies” were made of mortar, clay, and sand, and each “belly” is an original piece hand-made by sculptors. By the end of 2020, damp-proofing is to be ap-plied on the ceiling, and then the finishing of the crushed-stone walkway around the whole perimeter of the Ossuary is to be done. Together with the construction work in the “bookshop”, we continued with renovating the interior of the Ossuary’s lower chapel, with special attention given to the chapel’s problematic structural stability. Strengthening all of the pillars was suggested, using the method of widening the existing foundation structure by underpinning made of worked stone blocks with mortar of compressive strength 5MPa. The existing foundation of the northwest pillar was gradually, section by section, underpinned all around by a new foundation under the existing footing base. In December 2019 and the second part of January 2020, carpenter’s lagging was installed in four vault zones of the north-west pillar, and during February and April, the northwest pillar was underpinned. The plan view of the trench was a square with sides of almost 5 m. The depth of the trench was approximately 1.5. m. The foundation is underpinned by four rows of worked stone blocks and fastened by stainless pull pins. After the underpinning was finished, the foundation was covered with a mixture of gravel and dug-up loess loam, foam glass was added in the upper layer, and everything was thoroughly com-pacted.