My installer wants to use Ardex to level an area of concrete that is attached to a room of plywood in order to install a hardwood floor.

Then he is planing on taping down 6 mil poly and then attaching 5/8 cdx new ply to the concrete and wood floor via fasteners-"he seals the holes" and then he will glue my 7/16 solid to the new ply.

But I am curious regarding the ardex and it's possible breakdown. The uneven area is in a hall where much foot traffic will be. The ardex will be under ply and poly but I wonder if it could crack because of the concrete fasteners and nails and provide a crunchy floor??

Also, the current subfloor has old paint and gunk all over it. He does not sound like he is going to bother cleaning it off. I think he is just going to dump the ardex on it as is. Is this ok???

I would like the floor to last 25 years.
Thanks in advance!

Ardex is some bad arse stuff!! It is the best. Nothing compares. It is expensive, compared to other sundries suppliers. I like their SD-F for most applications, Although I will use Mapei PlaniPatch Plus, for deep fills and cap it with a skimcoat a Ardex SD-F

OK then from your response I hope I can [i]assume[/i] that my fears are unwarranted. The instructions on ardex say to clean the floor first so I was concerned.

Yes, the substrate needs to be free of any loose debris and contaminants. Latex paint is the big bond breaker, with Ardex.