help, what to use for under bathtub

We are installing a drop in tub and I'm trying to find the best product for under it. There is about 3/4" between the feet on the tub and the platform that is there.




I tried the top one and I may have mixed it too wet as it is just crumbling now

thanks in advance!

Trevor

I have successfully used the top one (mortar mix) for decades.
Of course it has to be wet enough to move around, but it should be as dry as possible, i.e. not a slurry You should be able to form peaks.
We leave space between chunks so that the mortar has room to spread. Of course, it is ideal to have eyes on the open space and pack it in from open sides, but you don't always get such an option on remodel work.

Am I being too impatient on it setting up? It has been about 15 hours and if I poke at it with a screwdriver chunks will break away and then crumble. I'm afraid once they close up the front of the tub panel tomorrow it will then just crack out from under the tub over time and we won't have access to it again.

With such a small amount of distance between the feet and the bottom I'm afraid if I mix it drier it will not push out of the way enough.

I'm wondering if I'm over reacting at the condition of the mortar.

If I jab at it with a screwdriver it will chip away but jumping up and down in the tub at the area the feet are doesn't have any effect on it.

I'm up against a time limit though as they are coming out tomorrow to close in the front access to the tub