Floor tiles need a solid inflexible base in order to prevent the tiles from moving over time and so causing cracks in tiles and/or grout lines. 10mm thermal tile backer board is ideal for this purpose since it also provides excellent insulation, particularly valuable if undertile heating is also to be fitted. The WetBase is 20mm thick ,approximately the same as conventional floorboards, and so in order to achieve an even level floor area throughout, the area beneath the wetbase needs to be raised by 10mm using a section of 10mm tile backer board placed across the top of the joists and its supporting platform.
By over-boarding the floor boards with insulated tile backer board, (and taping all joints) a level, stable and waterproof floor is achieved ready for tiling.
Please see the WetBase installation instructions for full details etc.