In general it is not recommended to use the Siniat DIrect Bond Lining System below ground level or on any substrates subject to moisture ingress. A mechanical fix lining system, should be used instead.

The nature of the gypsum bond would absorb moisture over time which can lead to the degradation of the bond. 

If the back ground is treated to prevent moisture influx, this will also likely prevent the use of the direct bond as it seals the surface. The gypsum bond requires a degree of suction from the background to form the bond properly.  In such circumstance, it may not be allowed to penetrate this tanking system restricting the mechanical lining to an independent (IWL) type which would not require support from the substrate.