Restoration of listed historic buildings by means of a post-construction damp-proof course taking the Bad Doberan gatehouse as an example
Rising moisture is the most common cause of moisture penetration in brickwork. The most efficient method of sustainably repairing damage is capillary obstruction of one brickwork level by installing a post-construction horizontal damp-proof course. This effectively eliminates the capillary absorptivity of the brickwork and restores the natural moisture balance of the brickwork.
It has been tried and tested for many years, and it is state-of-the-art knowledge that high-grade, well-formulated polyurethane resins work perfectly in this context under normal conditions.
But what can be done if the brickwork is fissured, damp and also damaged by salt? This was examined by the Dahlberg-Institut für Diagnostik und Instandsetzung historischer Bausubstanz e.V. Wismar (DIW) when restoring the gatehouse of the Cistercian Monastery in Bad Doberan, Germany, with WEBAC Injection Resins.
While doing so, the state of dampness and salt damage before and after the installation of a post-construction dampproof course with WEBAC PU Injection Resins was examined on site and in the laboratory.
The monastery complex in Bad Doberan is one of the most impressive examples of medieval North German brick Gothic architecture. The complex is surrounded by a roughly 1.4 km long curtain wall. There are four entrance gates; the gatehouse is located at the west gate of the complex and was erected in the 13th century. Its present style dates back to the year 1763.
The gatehouse sits on a natural stone base connecting to a short, rugged brick wall and brickwork structure. The wall thickness varies between 36 cm and 51 cm. The post-construction horizontal damp-proof course had to be installed directly at floor level, which was partly in the area of the rugged brickwork.
At first, quick-foaming WEBAC PU Injection Foam Resin was pre-injected into the fissured brickwork to fill cavities and gaps and to prevent any uncontrolled emergence of the subsequently injected polyurethane resin. Low-viscosity PU Injection Resin WEBAC® 1403 was then used for the final sealing injection.
The state of dampness and salt damage to the brickwork was examined over a period of 42 months, i.e. before restoration, immediately after the injection and six months thereafter.
To do so, 3 to 8 cm long brickwork samples (drill cores) were taken at three defined measuring axes. The moisture content, moisture saturation, degrees of moisture penetration and salt content of the drill cores were determined in the laboratory. At the same time, electrical measurements on moisture distribution in the brickwork were performed at the measuring axes.
It turned out that, at total degrees of moisture penetration of up to 99 %, the post-construction installation of a damp-proof course by injecting low-viscosity PUR Injection Resin WEBAC® 1403 is possible despite strong jaggedness and fissures and significantly reduces the water load on the brickwork.
The partly high load caused by hygroscopic salts has no influence on the effectiveness of the injection material.