To ensure the long-term preservation of the historic building, the state of North Rhine-Westphalia, as the owner of Augustusburg Palace in Brühl, commissioned the restoration of the terrace complex. Sealing countless intricate details, dealing with unpredictable weather conditions, coordinating with various trades, and complying with historic preservation regulations were the most significant challenges in the renovation of this UNESCO World Heritage Site. To protect the structure from moisture intrusion in the long term while preserving its original character, the use of the Triflex BWS balcony waterproofing system proved to be the optimal solution. The liquid polymer, based on polymethyl methacrylate (PMMA) resin, conforms precisely to complex structural elements. The system was specifically developed for waterproofing beneath existing coverings and offers permanent resistance to alkalis and hydrolysis. As a result, the old natural stone slabs of the terrace could be reinstalled after waterproofing with Triflex liquid polymer.