Toilets, Sinks, Showers, Tubs and Disposals - what should tub and shower sit on?

I have a 60" x 60" corner jacuzzi tub and also a 48" x 34" shower pan that my plumber is going to set. He has gypsolite plaster sitting at my house that he intends to use. But the instruction manual for the shower says:

"mortar cement is required to level an uneven subfloor. Do not use plaster, gypsum cement or drywall compound for this application, as these materials do not provide adequate structural support"

so, I don't think this is right stuff to use. I have not found anything this specific in the manual for the jacuzzi, but I don't have time right now to look some more as I have to leave. I am not really leveling with it, the floor is already level. for the tub, we will have corian placed and then the tub will be set on the material he bought and then pushed down to get about 1/8" gap between tub lip and corian, which will then be caulked. the layer of gypsolite plaster, or whatever is used, will be about 3/8" thick-at max. so do I have to create a scene and tell him that even though this is what he always uses, it is not right?

Well, he's just using the plaster to provide support for the floor of the shower and tub. Thats very common, though many newer tubs and showers say they don't require any additional support. Most have a "web" of molded supports on the bottom. There should be something in the install instructions addressing whether additional support is required or desired.

The lines you quoted were only addressing the actual condition of the floor, not the setting of the unit.

the shower pan does have a web. I actually am not too concerned about the shower as it really doesn't have that much weight-just the person in it and a little water. but the tub will weigh quite a bit. I don't know offhand how many gallons of water it holds, but with the weight of water and two people, I am sure it is a lot of weight. and it will be sitting on maybe 10 4"x4" pads on the bottom that will be sitting on the plaster. if it gives way at all, the tub could shift and the lip could contact the corian causing either the corian to crack or the tub to crack as neither could support that amount of weight.

Ok found total weight for tub--estimated at 1264lb. found this in the manual:

Materials that may be used are a floor leveling compound,
mortar, plaster or minimal expansion structural foam having a density of a minimum of 5 lbs/cubic ft.; however the
bath must remain level in order for it to drain properly and all foam feet must make full contact with the leveling
material.

so I guess it is OK to use the plaster. surprising. I didn't think it was strong enough to support that kind of weight without crushing.

I personally have had good success with the installation of mortar bases on shower bases and/or tub/shower combinations.

Ok found total weight for tub--estimated at 1264lb.

That is quite a load for a relatively small area. Does it say anything about any additional structural support at the joists? Mortar will add even more weight to the floor. Is that rating empty or full of water/people?

no, nothing mentioned about additional support. The tub was on the drawings, so that should have been factored into the load calculations when framing was designed. they are 11 7/8" wood I joist (boise cascade AJ 20) with a span of 18' 7 1/2". That weight is for full of water and people and will span I believe 4 joists. what weight they use for people I am not sure. what is water-about 8.3 lb/gallon and tub is max of about 89gal and tub weights 122lb. that adds up to 861. that leaves about 400lb meaning they used about 200lb for each person.

Ahhhh. Okay. Just thought I'd bring it up though. Thanks. Interesting.