Do I cement Hardy backer board to the floor?

[ColinM50]

In the process of ripping out the bath and replacing with a shower. The shower tray will be on a plinth to get enough drop for the waste so my plan is to build up a 5 or 6 inch frame, for the shower tray and put the hardy backer board on that frame then the tray on top

Now the Q is, do I need to put say 12mm ply or OSB on top of the frame before putting the HBB down and do I put cement down on top of the HBB before placing the shower tray?

Advice I've had from tile supplier and tray supplier is conflicting. One says yes t'other says you can but probably not necessary.

What would/did you do?

TIA

[Slagathore]

ColinM50 said:

In the process of ripping out the bath and replacing with a shower. The shower tray will be on a plinth to get enough drop for the waste so my plan is to build up a 5 or 6 inch frame, for the shower tray and put the hardy backer board on that frame then the tray on top

Now the Q is, do I need to put say 12mm ply or OSB on top of the frame before putting the HBB down and do I put cement down on top of the HBB before placing the shower tray?

Advice I've had from tile supplier and tray supplier is conflicting. One says yes t'other says you can but probably not necessary.

What would/did you do?

TIA

I'd want the plinth as solid and rigid as possible, so would probably go with some Birch Ply (sealed/primed etc) or the No More Ply floorboard panels. They are incredibly strong. With their glue and some screws on to the plinths, that's probably as solid as you could get.

That would also eliminate the need to use HBB under the shower tray as well.

Then a flexible adhesive bed to put the tray on.

You can get pre-formed rigid foam trays with space for waste etc if that is easier? Then the shower tray can sit on top or some you can tile on to.

[andyxxx]

It would not be necessary, but you won’t harm anything by doubling up.
Just ensure the frame is 100% solid