I'm using walmanite 3' by 5' by 1/4" over an original Pine slate floor my grandfather put in. do i NEED to put some type of barrier like tar paper between them? there has never been a barrier and no insulation. my mother added padding and carpet but now she wants engineered bamboo clip together floating floor that will have a moister barrier padding between it and the wolmanit.
The floating floor needs the thin foam pad for it to function properly and most of the floating floor pads already have a vapor barrier as part of it. But adding an additional barrier is not needed (unless you have moisture issues).
If you where doing a nail down install (instead of float) I would recommend rosin or tar paper between the the floors. But it would not be for vapor barrier but to reduce noise between the two floors rubbing.