Glue underlayment to concrete subfloor

I have radiant floor heat inbedded in light weight concrete on the second story of my house and want to glue underlayment to the concrete. I have been reading a lot of similar posts but they are able to screw into the concrete. I can’t for fear of hitting the radiant heating tubes. Any recommendations on adhesives and just how flat does the light weight concrete need to be. Oh, my finished floor will be Armstrong vinyl composite tile. (not the self-stick) Thanks for your help.
Replies
Can't you put the vinyl tile directly on the concrete?
Two adjoining floors are about half an inch higher than the concrete. Tile in one room and engineered hardwood in the other.
chuck
is this the same room (laundry) that was a problem in your other post?
You should have left these questions in the previous thread-background would have been taken care of .
but, if a small space-to add a qtr inch-maybe 1/4 inch tile underlay-bed it in PL premium or look to bostik for a proprietary adhesive (better idea) to glue it down. Hit the seams and surface (skim coat it) with Dependable crack filler. Light sand and put down your vinyl tile.
or, leave lower, install a transition pc at the openings.