Tiling over USG LEVELROCK brand gypsum underlayment - Advice Needed

[cjhusky]

Just recently stumbled upon this site, doing some research. Tons of knowledge, experience, and passion in here.

I've spent the last few hours reading through the forum posts on tiling over gypsum underlayments (mostly gypcrete brand) and there is a lot of great information here. I have not however, seen much information posted with regards to USG's LEVELROCK product. It seems that in reading the instructions for installing finish flooring requirements for these products, that there are differences in these products and their requirements. So I'm hoping that some of the professionals with experience in laying tile on this type of substrate can help us out.

I'm the GC on a residential job that's about 5,000SF. Nearly 1/2 of it is til (porcelain, ceramic, travertine, and slate). I have a single-shingle sub that's doing the tile install for me on this job and he's awesome. However, neither of us has experience with laying tile over LEVELROCK, or any other kind of gysum-based underlayment for that matter. I want a quality job, but cost is a factor, as I had not planned on needing to use NobleSeal TS or Ditra. They are great products, but overkill IMO for this application. In fact, in one of the docs I'm attaching, they claim Custom Building Products provides a 10-year warranty with their FlexBond Fortified Thin-set mortar when used over the LEVELROCK in place of a crack isolation membrane. Does CBP warranty the same for other gypsum-based underlays (i.e. gypcrete, etc.) or only LEVELROCK? It sure looks like you could get a darn good bond to this stuff with just a modified thinset.

Here's the details of the job:
Floor joists are TJI's (engineered 11.5" I-Joists) at 16" o.c.
subfloor is 3/4 T&G plywood
LEVELROCK underlay is 1.5" thick with 1/2" radiant PEX tubing embedded
LEVELROCK was primed by the sub that laid the product; I'm checking with them in the AM, but I believe it was the SE-100 primer that is spec'd
LEVELROCK is DEFINITELY dry! READ: It's been in place for nearly 6 months and has had heat going through it virtually the whole time.
My only concern is that I've had several rough subs in there since the LEVELROCK was laid, including sheetrockers, mud, tape, texture, and painters. They've made a mess of the floor, but not in terms of chuncks or anything, just paint overspray and lots of dirt to sweep. I think USG says you can verify the integrity of their primer using a black light, so I'll try that and see if additional coats of primer are needed.

So for the folks tht have past experience here, with relatively limited deflection given the structural support here, is it reasonable to assume i can just go with a modified thinset mortar here for my tile and stone? Other recommendations, advice, wanrings, etc, would be much appreciated.

I've attached the documents I have about the USG LEVELROCK product.

Thanks in advance!!!

-Chris