You'll have several other issues caused from using the wrong material.
Biggest one is the tub is now unsupported and may crack.
Even if at some point it does hardens up by now someone has likely stood in that tub and compressed the mud leaving a gap.
Biggest one is the tub is now unsupported and may crack.
Even if at some point it does hardens up by now someone has likely stood in that tub and compressed the mud leaving a gap.