Had an acrylic shower base (single threshold) installed by a plumbing company. Come to find out the base is not level and when the shower is on the water pools to the back of the shower, it eventually drains but its takes aboout 12-hours to be water free in the base.

When it was installed I asked the plumber about using thin-set mortar to set the base in for additional support etc.. He recommended using sand and not to use the mortar. So I went with his professional opinion.

I called them about water pooling to the back of the wall and they said the floor wasn't level and that even if they used the mortar bed to set the base in it, it still wouldn't make the shower base level. They said I need a carpenter to come in to fix the floor in order to make the shower base level.

I am not a professional installer of shower bases but based on what I have read setting it in a thin-set mortar base will make it firm and when you push it down in the mortar base that's when you level it?

Trying to get a correct answer on this as I think they took a short cut with the sand recommendation. No shims were used either.