Last month Steve wrote this:
However, last year he wrote this:. . . your badly damaged original floor could be leveled with gypsum joint compound before adding a layer of gypsum (I'd use the "greenboard" version of gypsum, made for bathrooms, etc, since this is a floor and possible wetting may happen from mopping, etc) - then, I'd put a solid layer of MDF or OSB on top of the gypsum. . . (Source)
So, I think the answer may depend on whether or not you're floating your walls on it. :roll:I'm not a fan of using particle board as a bottom layer of floors that are over concrete - moisture and particle board aren't a good combination - also, if you're going to float the entire room on top of this floor, I'm not sure if using a sandwich of gypsum in the floor is a good idea either - I've not done this, and I'm a bit leary of that much weight pressing down on a particle board and gypsum floor without compression problems. (Source)