Choose a small tile 4 inches square or less.
How to straighten a wall before tiling.
Scrape the wall to remove any texture and to create a flat surface.
Hi you can chip the old glue off and loose paint and patch the walls to make a level surface for the tiles.
Remove any remaining dust oils and grease from the wall with tsp tri sodium phosphate or an ammonia based cleanser.
I cannot tell you the last time i tiled a perfectly flat shower and unless you are using mosaics or really small tiles you will have to vary your thinset application to fix any issues.
Then address any unevenness of the studs with furring strips or shims.
Inspect the drywall carefully to ensure it is securely screwed nailed to the studs.
Your answer is that you would deal with bowed walls by using thinset on your tiles.
Since the wall is open i would replace all the electrical boxes with the new adjustable depth boxes so you can set them to match your tiled wall.
Follow these other prep steps to prevent having to redo the job.
You would simply use more thinset on the parts that are in more and less on the bowed areas.
Seal seams on new drywall with drywall tape and compound and let dry.
Check the wall first to see if it is straight.
Patch any holes or cracks with spackling compound and sand the entire surface with medium grit sandpaper.
I would take out off the drywall if not from the whole wall then from the cabinets up take off the window trim casing and sill.
One handy tip my father in law taught me three years ago was if you plan on tiling a wall and the wall is uneven then the plastering doesn t need to be abs.
Wipe down with a damp cloth to remove any remaining.
Vacuum to remove dust.
Slide a 4 foot straightedge or level over the wall in all.
The smaller the tile the less it will show on a bowed.
I use csr cornice cement for patching it works well sticks to the paint also.
If the walls aren t clean the adhesive won t adhere to the walls and neither will the tiles.
Where the shower is and other wet areas are you will need to chip the old render off back to the brick and use a cement render as a waterproof base for ghe tiles.
How to tile walls that are bowed in the middle.