I m guessing its the thickness of the dot and dab then plaster board then tile adhesive then tile.
Gap between floor and wall tiles.
The tile council of north america recommends at least a quarter inch gap between the tile floor and the walls.
Caulking is the best choice for this application.
Gently push the tiles together so the spacers are tight in the joint.
As the tiles increase in size a larger gap becomes acceptable.
It might loosen them and might rot the floor.
If you have tile on the wall adjoining the tub select a caulk that matches the color of the grout.
These can be left in place and will not be seen when you have completed your tiling.
Gap between floor tiles and wall tiles.
Fill gaps larger than 1 8 inch.
The gap goes 3 5cm to 4cm back to the breeze block.
The large format 18 inch tiles should have inch space in between.
For smaller tiles is advisable to use small spacers.
Instead fill it with an elastic material capable of sustaining the movement of the floor and the movement of the wall.
Not filling the gap can allow water to migrate undeneath the tiles.
It shows how to seal a gap in the corner where the tile floor.
To read the rest of the thread look here.
Gently spread the tiles and place two spacers between them one at the top edge of the seam and one at the bottom edge.
The d i y video how to seal a big gap between tile floor and tile wall in a bathroom or shower.
If your gap is smaller than 1 8 inch in width use regular caulk.