Shower Base flexes after mortar bed installation. Advice?

[Tuttles Revenge]

Is it only flexing in that one corner or the whole pan overall? If its just the corner, then packing, stuffing in bags, cake icing is the likely solve.. I would go the extra mile now and do that around the whole thing..

And the super easy solve for this shower pan is to apply a self leveling compound and avoid trying to shim..

 

[Zerocool749]

Hi everyone!

A couple days ago, I used everyone's advice and fixed the problem! I cut a notch in my bottom plate, filled a mortar bag, and backfilled under the shower base. I left the pan flexed up and filled with mortar for support. Now, it is rock solid when I step in the area. The back area of the shower base is a little out of level, but nothing too bad. My first row of tile will cover that.

If you look close, you can see the notched bottom plate. There is another bottom plate made of pressure treaded lumber underneath, anyway.

Thank you all again!