Yeah well even Franklins Titebond 531 Plus twp part epoxy system will not warranty it below grade. Their system is one of the best.
Read this very carefully. And especially the warranty part at the bottom of the page - Exclusions from Coverage
Then since he had SLC put down it needs to conform to this:
"If filling/flattening compounds are used, they must be Portland-based cementitious material and have a compressive strength equal to or greater than 3000 psi when cured. When using cementitious materials, they must be rated for the moisture content in the concrete slab. Always use the highest rated materials for moisture because the moisture levels will change."
Even their best all in one adhesive thats rated for below grade - the warranty also states "
Exclusions from Coverage
The above warranty does not apply if: (1) all instructions regarding preparation for, installation and use of flooring products and this Product are not strictly followed (2) the Product is used as an adhesive and moisture control for below-grade applications;"
Always read the fine print.
Now Stauf has a Level-Seal ULC 500 that says nothing about NOT using it below grade whoever you better consult with their technical dept. They also have a product called
ERP-270 Perma-Seal.
http://www.staufusa.com/index.php/259/@.html?articleID=9500&action=detail
I'd say that if I were going to touch this job I'd do sealer, plastic then float. I've done sealer, plastic,felt then floating plywood with a nail down solid wood floor successfully. But that was built into the side of a leaky mountain, not totally below grade.
If there's NO vapor barrier under the slab fahgetaboutit.