I remodel/repair for a living, and cannot see why you would thinset
anything to waferboard/OSB etc. I wouldn't be as concerned about the
waferboard dissolving as I would that the moisture would suck out of
your thinset too fast and you would just have a sandy mix underneath
your cement board.
If you want to use the cement board, try glueing your board down and
screwing it to hold. There are many good glues available for this,
just check with your tile supplier.
I would suppose that this floor is either a second story floor, or a
floor in a pier and beam house. You should know that the cement board
will work itself loose after a few years of foot traffic on a floor
that flexes, as I mentioned above. The screws hold fine, but the head
wallows around and "works" inside the hole until it is loose. Then
your problems start as it will soon start to crumble underneath. There
may be some out there, but I haven't seen any cement board that is
intended for weight bearing/foot traffic underlayment.
Here's what I do:
I put down two layers of 1/4" tempered masonite (the brown stuff, no
pattern - think peg board without the holes) making sure the joints are
perpendicular to each other. The first layer will act as a slip sheet,
and allow the floor to flex without harming your tile.
We nail this down with 6d sinkers (flatter heads than screws, and they
don't make a mushroom in the masonite) and do NOT use any glue or
adhesive. Tack the first layer down, then nail the snot out of the
second layer. When the second layer is installed and finished, we
spray a latex bonding agent on the floor similar to the stuff the
wallpaper guys used to seal a wall.
The tile is then installed with latex mastic, and grouted as usual.
My old tile guy showed me this 25 years ago, and I have never had a
complaint since I have done it that way.