Tiling a slope

I'm not sure what a 'backover' sloped wall is - do you mean a ceiling which slopes at 45deg? So that the face you're tiling would be facing slightly towards the floor? If that's the case, then you need a stiff acrylic pre-mixed tile adhesive. This will work fine.

If you mean a slope where the tiles are still above the solid material, then it must be the same as a vertical wall, do a couple of rows at a time .....

If you mean like a sloped celing, then I would guess they would stick, if you can hold them while the glue dries ......... Rick

Use a good quality high grab adhesive. And a hard hat...

Christian.

P.S. I've stuck tiles upwards onto a horizontal bed without issues before. I was using a top of the range BAL readymix for this. I think it was "White Star". The one suitable for commerical swimming pools, anyway. I used no specific restraints to do this, although it was a soffit only one tile thick, so I wasn't too worried about consistency of face position.