The mortar is spread.
How to tile over uneven walls.
Hold the float at a 45 degree angle to the.
As for the floor being out i would pick a comfortable height the lower the better and establish a level line and back lay the tile to the floor but i would not do that if you are really talking about true cove tile because you will end up with a cut edge on.
Mark the wall in the middle with a chalk line to create a guide for the tiles.
Back buttering is a trick used for tiles of uneven thickness like ungauged slate or handmade tiles extremely large tiles or for tiles being installed on an uneven surface.
By uneven i think you mean that the walls are not flat.
The floor slanting is not that much of a problem even for a do it your selfer.
With a notched trowel apply the adhesive at the bottom of the cinder block wall.
Spread grout over the wall tiles with a grout float a rubber tool used for spreading grout.
Don t use plaster or ordinary sand cement render or you will have to wait a minimum of 10 days before tiling longer the thicker it gets.
Apply just enough of the adhesive to attach a few tiles at a time so that the adhesive stays moist and ready to receive the tiles.