Tiling Walls That Are Not Plumb
Slide a 4 foot straightedge or level over the wall in all directions to check for plumb.
Tiling walls that are not plumb. Subway tiles are notorious for not being well made so i always tile all 3 walls at the same time so the grout joints match up on adjoining walls. Its logical to do one wall at a time but it doesn t work out that way. Do this prior to any tiling job. Check the wall first to see if it is straight.
The horizontal line assures the 3 walls are level with each other and the grout joints will line up wall to wall. Answer answer what should have been done while installing the hardibacker board on the walls is the framing studs should have been shimmed and adjusted to make sure the hardibacker board was plumb and square. Lippage can be eliminated on most walls by hanging new drywall or backerboard before tiling.