On Charles Bridge, more stones need to be replaced than expected

Prague - During the renovations of Prague's Charles Bridge, workers will have to replace many more stone blocks of the parapet than originally anticipated. According to heritage conservationist Ondřej Šefců, the mistakes made during the reconstruction of one of the city's most significant landmarks in the last century are to blame. The stones were set in hard mortar, and voids were filled with cement. This trapped water, which damaged the stone blocks.
    "The stone did not benefit from that. Using natural stone in cement mortar is a great crime," Šefců told ČTK, who is supervising the current repairs. Many stones that could otherwise remain on the bridge are, according to him, in such poor condition that their reuse is inappropriate both economically and from a heritage perspective. Four to six blocks out of ten will need to be replaced. "We are finding quite terrible things," he added.
    According to information from the construction company SMP CZ, the parapet is being dismantled one to two rows of blocks below the original roadway level. In places where cement was used, the joints must be sawed with a diamond chain saw. The company stated that the stones have also been damaged by salt. "Practically the entire row of stones below the roadway is damaged," the company indicated on its website.
    The renovation of Charles Bridge began last August. According to Šefců, the bridge segment on the northern side near Malá Strana has been rebuilt, the section near Čertovka is currently being built, and the section at Kampa has been dismantled. The main reason for the reconstruction is to install new waterproof insulation so that the masonry does not tear during water infiltration. The bridge will also receive better ventilation.
    The insulation laid during the restoration project that ended in 1975 was already faulty by the late 1970s, according to Šefců. "It was typical for that time that the first faults appeared three years later," noted the heritage conservationist.
    The current renovation, costing around 220 million crowns, which should be completed by mid-2010, is also accompanied by archaeological surveys. Near the Malostranská Bridge Tower, archaeologists uncovered the side of the bridge. The stones bore marks similar to those on the bridge tower. The repair project had to be modified, and the masonry was preserved. Experts also uncovered ceramic shards, the oldest of which likely date back to the 8th to 9th century. Their age corresponds to the area's earliest settlement.
    Another survey was conducted to determine where the bridge ends in Malá Strana. It is important to ascertain this so it is known how far the insulation should be laid, Šefců said. Archaeologists also conducted a probe at Křižovnické Square. According to Šefců, the theory that another arch exists there was not confirmed; it was not found. Excavation will also take place on the Old Town side to determine where the bridge ends.
    During the repair, new engineering networks will also be installed in the bridge, and gas lighting should be introduced. In the second phase, the stone cloak of the bridge will be reconstructed. All work is being carried out so that the bridge remains passable at all times.