Shower base nightmare

[TJ55939]

So I had a plumber/friend help me with my new 48 x 32 swanstone shower base. i tore up the subfloor laid new 3/4 in plywood down so I know it's good and sturdy. He wanted to use quikcrete mortar so I mixed it up to his desired texture (like peanut butter). He laid down about 3/4 in of it all the way around. One problem was that this shower base is so low to the ground that the tub was 1/4" off the ground after we tried to set it. After scooping out tons of mortar it started to set up and we couldn't get the base to sit sturdy (it kept rocking). I ended up ripping out all the mortar cleaning the area and the pan and starting over. I decided to use window and door low expansion spray foam instead of mortar which the plumber was okay with. He only wanted to use maybe 3/4 of the can. We set it in and everything seemed okay. I screwed the tub to the walls and already furred out the studs for durock. Went to stand in the tub today and it's creaking (mind you the shower drain is not installed yet). Should I rip the base out and do something else? Or maybe when he comes back to hook up the drain it will solidify the issue (I doubt it). I'm an electrician and I didn't sign up for this. Please help.

 

[Terry]

The Swanstone needs almost nothing. If things are flat, then often nothing. I mainly consider using mortar if things are out of level to help shim. I don't use expanding foam on a new install. I kinda don't see the point in it, as it can continue to compress with weight. You may have noticed that while working with that pan, it's rather sturdy. If I want to just stick something like that, I may lay a few lines of construction adhesive down and drop the pan down on that.
Mortar is mainly good if there are large voids below. For example, setting a tub on a deck, and using it to support the bottom of the tub so that the flange doesn't have to hold the weight of the tub when water is added. For that, I drop a few piles down that can squish out. Trying to do a full bed is pretty much impossible. It would be like magic if you could be so good that you can hand spread and have it flat and perfect.
The mounds I use under tubs just squish out and away, being pushed down by the weight of the tub. I don't need a full touching surface, just a few spots here and there that help to stablize.
But hey! All of what you have done now makes you much more experienced and crafty. It's how we all get there. I like to say I've made plenty of mistakes. Sometimes I try things to see why they don't work and sometimes to see if they will work. I collect all of that and refine how I do things.