So you ve got that bottom row of tile.
Tiling out of plumb walls.
If this is the case you could remove the first course of tile and cut the board above the flange punch the board in and screw it.
Find the midline of the wall from ceiling to floor and mark it with a chalk line.
I hesitate to bring this point up but i think guess your walls are out of plumb because you capped the metal upturn flange of the tub with the cement board.
Check your floor for level and walls.
A batten board helps you start your bottom most course or row of tiles.
How do we deal with that doing tile.
Tips for tiling a wall 1.
Install the wall tile in a pyramid shape.
Measure the wall where you will place the tiles.
Hang a batten board to prevent tile slippage.
You will lay out your first tile directly on this line and your.
We are doing a remodel and have discovered the wall around a tub shower is out of plumb by 1 2 over 5 feet.
If this is not the case then forget i brought it up.