St. Nikolai memorial church, Hamburg

The spire of the St. Nikolai memorial church in Hamburg is one of the tallest in the world. Although a few parts of the outer walls are virtually all that remain of the rest of the church, the spire still rises to its full height. Extensive refurbishment work was, however, necessary in order to secure and maintain the spire. Repairs to the masonry formed a crucial part of the work, with all the joints having to be repointed – a total length of about 40 km.

The consortium responsible for the refurbishment work carried out preliminary laboratory trials to establish the bond and shear strengths of various mortars. The TKF trass-lime pointing mortar from tubag supplied the most convincing results. An unusual solution was chosen to adapt the mortar to the special demands of the stones treated with a water repellent: A bonding slurry – TNH trass-stone bonding slurry from tubag – was used to enhance the bond between the sandstone or clay brickwork and the pointing mortar. Although this standard product was fine for some areas, the special conditions on the church tower called for a project-specific mortar. In the end, the building materials of the tubag (a Sievert SE brand) range which are specially developed for the repair of historic buildings proved to be a logistical advantage. For example, the consortium was able to make use of another tubag product to make good the masonry and the fitting of new stones. The tubag TWM trass cast stone mortar harmonises excellently with the pointing mortar and the bonding slurry.

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