Originally Posted by Brik
Only thing I have noticed is it seems to set faster when on wood than on plastic. Maybe it was just me. Also - I built a little dam out of cardboard to keep the mortar where I wanted it. stapled it to the ply deck.
Not just you; it will set faster because the wood will absorb the moisture from the mortar, whereas the plastic sheeting will prevent this, so the only drying will be from evaporation . I doubt if the moisture from a one time application like this would premanently harm the wood sub floor, but I routinely throw down some sort of barrier. Just whatever is around..felt, visqueen, house wrap.