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BAL Board under shower tray

Discuss BAL Board under shower tray in the Tanking and Wetrooms area at


New to the forum and my first post on this after doing a bit of searching. I'd be interested to know your thoughts/experience of fitting BAL Board or Hardiebacker under the shower tray. The reason I ask is that with the build-up i'm looking at, if I installed the shower tray on the ply base then the top of the tray (55mm thick) would be almost level with the marble tile finish.

The project is a bathroom refurbishment in a Victorian first floor bathroom. Joists are sound and level, old floorboards a bit ropey so i've replaced with 22mm WISA Spruce T&G Ply. Over that:
12mm BAL Board (or 6mm if I can get away with it)
Schluter Ditra Heat Duo (7.5mm thick integrated decoup and UFH membrane)
15mm marble tiles

If anyone knows the thickness of the bed between these layers it would be interesting to know, i've roughly allowed 5mm for adhesive bed, which means the shower tray is sitting proud by about 10mm or so. Not much room for error!

Thanks in advance,

Reply to BAL Board under shower tray in the Tanking and Wetrooms area at

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