Shower tray on decoupling mat?

[peteypops]

I'm fixing an acrylic shower tray to an upstairs bath room floor - moisture resistant chip board floor on posi-joists, all brand new. The surrounding floor tile will be decoupled, probably with DITRA. I currently have the standard tray-sized hole, filled with plywood plus mortar on top design.

 

It occurs to me that this might be overkill, why would I not just run the decoupling mat everywhere and thinset the tray to the decoupling mat? Vertical displacement is not going to be an issue, so I believe i'm really only looking to protect against differential expansion, which is what decoupling mat is specifically for.

 

Any thoughts on this?

[Temp]

I used flexible tile adhesive. Seems OK.  However some trays aren't very flat on the bottom or strong enough. The mortar base is intended to solve both issues.  

[peteypops]

I've used tile adhesive before to good effect, but as you say, that will depend on the tray itself.

[peteypops]

6 hours ago, peteypops said:

I'm fixing an acrylic shower tray to an upstairs bath room floor - moisture resistant chip board floor on posi-joists, all brand new. The surrounding floor tile will be decoupled, probably with DITRA. I currently have the standard tray-sized hole, filled with plywood plus mortar on top design.

 

It occurs to me that this might be overkill, why would I not just run the decoupling mat everywhere and thinset the tray to the decoupling mat? Vertical displacement is not going to be an issue, so I believe i'm really only looking to protect against differential expansion, which is what decoupling mat is specifically for.

 

Any thoughts on this?

Correction, it's a stone resin shower tray with an acrylic surface, so they call it acrylic.