Had to tear plaster off behind sink as it was damaged, now I want to install a new backsplash. I am left with a rectangular section of the wall that is the exposed lath. I thought cementboard would be the right kind of backer for the tile, but on top of the lath it is not flush with the plaster next to it. It is about 1/8 inch out of flush. Using 1/4 which isn't recommended for tile makes is -1/8 inch out of flush with the plaster. What's my solution?