It has been suggested to me that I can glue or float (2) layers of birch plywood over 1/4" black acoustical underlayment to raise floor to meet existing marble. I will staple 2000 sf engineer on top. I cannot put a fastener into slab. Any suggestions/success stories? Underlayment is installed. Please respond I'm kinda desperate for info, alot of $$$ here for it to fail. 3rd floor condo moisture not an issue for now. TT

The condos we used to work on, we had to put the black insulayment down, or cork. Then we would use 3/8 plywood, with another layer of 3/8 plywood baskeweaved (ran the opposite directon). Then we had to use 3/4 screws to fasten them to eachother (but not penetrate the sound barrier.) finally we followed by using 1 1/2 in staples on the 3/4 flooring, none of the fasteners were allowed to penetrate the cement.

Hope that helped