Performance of Lightweight Wet-Room Floor with Two Waterproof Membranes

The purpose of this paper is to present and evaluate the performance of a lightweight wet-room floor structure with two waterproof membranes with a water-resistant cast compound between the membranes (twin floor). The twin floor was developed for use in existing buildings with a reduced load-bearing capacity of foundation or floor division. A watertightness test in the laboratory clearly indicated that wet-room materials for structures with one membrane were workable in the twin floor. Hereafter, two twin floors were constructed in an existing building including sensors for measuring temperature and moisture content in the cast compound. Multiple moisture measurements and watertightness tests near one floor gully showed potential water ingress in the cast compound through either the primary membrane, floor gully, or their assembly. Neither in the laboratory tests nor in the full-scale twin-floor tests was water penetration through the secondary membrane observed. In conclusion, the twin-floor showed promising results for working in practice. However, a redundancy layer is crucial to implement in the twin floor, because of the difficulties in testing and constructing the twin-floor structure.