Shower enclosure issue where wall meets the floor
After tearing down the existing walls in my shower enclosure, I found that in the original installation, the contractor put up the wonder board walls first, then poured the concrete floor, so now I have nearly a 3/4" gap between the stud wall and the finished floor. Should I just leave this gap there an bring the new backer board down to the level of the floor (Option A)? Or should I fill in this gap with concrete before hanging the new backer board (Option B)?
There are parts of the floor where the old backer board could not be removed, so I'm not able to push the new backer board down into the space uniformly. The shower pan membrane is under the concrete floor and extends up the wall about 8", so I feel ok if water gets into the space.