more mortar bed questions
I'm about to set a tub w/mortar bed and have some follow-on questions to this thread. Here's the background:
-Acrylic drop-in tub, 3-wall alcove installation
-Bottom of tub is 1/2" off floor at drain end and about 3 1/2" off floor at opposite end (all edges level and resting on stringers (ledgers?))
I've estimated that I'll need about 1.5 cubic feet of mortar. Based on other posts, I was planning to use Structolite gypsum plaster for this.
I've seen two contradictory posts about whether to put poly sheeting under the mortar in addition to on top of it. One said pour directly onto ply subfloor, the other said to use poly underneath to protect moisture from wicking out and drying mixture too quickly. Which is right? Does it really matter? Either way, I will put the poly between the mortar and tub itself.
Also, are there any issues with using Structolite in a thick application like this (up to 3 1/2")? Seems like other tub sets only require an inch or so. Will it set properly? Can/should I add a little regular quickcrete mortar to the mix to help it set? Is Structolite the lightest weight product (more or less) that would be appropriate for this application, or is there something else I should consider?