Acoustic Board under tiles

I have just removed old tiles from a small shower room. The acoustic board lying beneath the tiles above the concrete floor had turned to mush and there was a lingering smell of mould.

I will have to replace the acoustic board but don't want this to happen again. Does anyone know of any new types of board that are suitable for bathrooms or wetrooms. Or do i need to ensure the new tiling is sealed very well. Any ideas?

I dont know anything about "acoustic boards" under tile on a wet room floor.

If you posted pics of the floor and the bathroom it would help.

There's a vast range of boards and preparations for bathrooms but first you/we need to find the cause of the "leakage"?

you cant really reliably seal tiling. using a cement based backerboard would be the best choice, or tank the surface prior to sealing (this is a membrane that can be painted on or used as a sheet)

accoustic board would be unusual, you'll usually discover plasterboard behind a shower like that