Some tubs need to be installed in a complete mortar bed, other manufacturers actually prohibit the use of a cement bed and they just get their feet adhered to the subfloor with construction adhesive. Different manufacturers have different requirements. Read up to see what your tub needs.

It does look like the base platform that the tub sits on is is really out of level and he used the mix under just the left end to prop it up a bit.

I do have a question...is the tub properly supported at the back right corner? It looks like the left feet are on a plywood shim plus a mortar bed. It looks like the right front foot is just on the platform base (or subfloor). I don't see the black "knob" on the rear right foot. Is that rear right foot dangling in the air, or is the white support block on that right rear corner actually (and adequately) supported by the thickness of wood that looks to be mostly behind it?

Thanks, Mongo.
According to the instructions for the tub (Kohler K1013 Portrait drop in soaking tub), the tub should be set in a mortar base with the leveling blocks (feet?) resting directly on a level subfloor. The mortar is not supposed to be under the leveling blocks according to the directions. The right side of the tub is floating 2 inches above the subfloor--not resting on anything.

The plumber is insulted that I questioned the install. He said he would do what I want (what should I want him to do?), but he has installed many tubs before and what he did was appropriate. He said the mortar is merely to support the middle of the tub. He said he did not use plastic between the tub and the mortar because he sprayed the bottom of the tub with silicone since plastic sometimes tears. This sounds reasonable to me. He said that he could spray foam under the right side if I am nervous about it not being supported on that side. I have read that foam insulates, but doesn't support the tub. I'm also concerned that rodents are attracted to the foam. The project manager (not a contractor) said the foam dries very hard and should work. Basically, the tub is resting on that bit of mortar--and hanging from the tub deck above the subfloor everywhere else.

What should I do?

Thanks!

When a manufacturer stipulates that the bottom of the tub must be supported by a full mortar bed, if it's not you'll likely end up with excessive flexing in the bottom of the tub when it's used.

Not all tubs are engineered the same way, thus the varying installation instructions.

Why let him gamble in your house? He can roll the dice somewhere else. While it's unlikely that you'll have an actual warranty problem with the tub (versus an installation problem), should you ever have a tub problem, Kohler will walk away since they'll have the "get out of jail free card" of the tub not having been installed according to their specifications.

So simply have him install it IAW with manufacturer's instructions.

That way there will be no guessing about future tub flex or movement issues, both of those can lead to noise when weight is put in the tub. Nothing worse than a squeaky bath.

Not all tubs are engineered the same way, thus the varying support methods in the installation instructions.

Closed cell foam does cure hard, but it still flexes, and over time it can shrink. Foam is fine as an under-tub filler (not for support, just as a filler) for me for tubs that don't need to be set in a mortar bed. Foam can provide a little extra sound deadening and additional insulation. But again, I don't depend on it for structural support.

Sheet plastic is a better slip and release agent than silicon. And faster. And less messier. And cheaper.

It's pretty easy to dry set a tub level and at the appropriate height over an unlevel subfloor, then measure the distance between the feet and the subfloor, cut infill blocks of the appropriate height, set and secure the blocks, then lift the tub, place the cement bed, then reset the tub so the feet are on the support blocks and the remainder of the tub base is supported by the mortar bed.

I used to be a rocket scientist, and this ain't rocket science. You are correct to want to have this tub reset. Your plumber shouldn't be insulted, he should simply improve his work methods. Do it once and do it right. As he'll find out it's easier, faster, and less expensive in the long run.

"but he has installed many tubs before and what he did was appropriate"

Well................he is an idiot !

I don't care how you slice it up, or how "he's done it for years", - leaving 25% or more of a tub unsupported and floating in air is not only inappropriate it IS SIMPLY NOT ACCEPTABLE - anywhere !

Mongo is right - let him gamble somewhere else.