If it seems complicated try this.
How to tile a wall that is not flat.
You already have a backsplash that 4 piece of countertop up the wall.
Pull the tile up and look at the pattern that is create on the back.
If the tile has been cut make sure you re placing it in the right spot.
I butter the back of each tile but scrape off any excess adhesive and put the tile on wall and twist it a few times holding opposite corners.
A contractor was giving me an estimate on a tile job and he showed me how my walls are not flat.
Spread thinset mortar on the bottom center of the wall.
Spread the mortar with the flat edge of the trowel then groove the mortar with the toothed edge until it is uniform in depth.
Putting tile on top of that doesn t look good especially w a busy pattern countertop that you ve chosen.
He held up a straight edge against the surface and showed me where some of my walls back off away from being straight in some areas.
Mortar a small spot and then place a tile.
The best way is to arrange your wall tile in a pyramid shape.
If you can remove it cut off the back piece and scribe it along the wall.
Apply it to the tiled wall with a grout float making sure to get grout into all.
If you wanted to do a tile splash you should have forgone the 4 rolled back piece.
Then every subsequent row is a process of draping over the pyramid back and forth.
Test a tile to make sure the mortar is mixed and spread correctly.
Install tiles one through four as directed.
So the tiles end up not being flat to each other but it doesn t seem possible to correct this as if i squash down on the one side the other side pops up.
The plan is to use large tiles 12x12 then he said he d correct for it by floating the necessary tiles out a bit.
Take a tile for the edge of the wall and apply the adhesive to the back as if you were putting butter on a piece of toast.
In your case make the top edge level and do your cuts at the bottom whether or not you use base or cove at the bottom.
The way i would approach this would be to get your top row correct and level then work down to the floor.
The other alternative is to run the wall tile doewn behind the floor tile with a 90 degree corner there.
For the average small wall tiles which are currently popular you will want to use a 1x4 square notch trowel.
Grout any tile job by mixing powdered grout and water to the consistency of peanut butter or use premixed grout.