I regularily use a mixture of washed sand/
cement /flexible adhesive when bedding limestone flooring that is uneven in thickness or if screed is too far out of level.
If you use sand /
cement mix only min bed is 25mm plus old school used a
cement slurry on back
tile .
But with this mix and as long as you use plastering / washed sand can quite easily get a solid bed under stone down to 6mm thick.
I still use very thin coat flex adhesive all over back of
tile and on screed . so you make a sandwich of your mix in between.
MIXING PROPORTIONS:
I PART
CEMENT ( 1/2 BAG ) 12.5 KG( PREFERRABLY WHITE COZ GREY HAS REACTION WITH PALE POROUS STONES SOMETIMES)
I PART FLEX ADHESIVE ( 1/2 BAG 10.00 KG.)
3 BAGS X 25 KG WASHED SAND.
MANY STONE FIXERS USE THIS METHOD BUT IT IS NOT GUARANTEED BY ADHESIVE MANUFACTURERS OR ANY ONE EXCEPT YOU IF YOU FEEL HAPPY WITH IT.
IT SAVES ENORMOUS AMOUNT OF MONEY IF SCREEDS OUT OF LEVEL AND YOU HAVE TO LEVEL UP.
BUT YOU CHARGE MORE TO LAY STONE AND SORTING THEIR WRONG LEVELS OUT.
I HAVE USED THIS ON QUARRIES AND CERAMICS BUT DONT TRY ON PORCELAIN AS TOO DENSE AND NON POROUS.
DONT WALK ON TILES THE FOLLOWING DAY AT ALL.
DONT JUST PUT FIVE BLOBS UNDER TILES IT SHOULD BE SOLID BED.
CAN CAUSE SALT PROBLEMS WITH TERRACOTTA.
HOPE THIS IS OF HELP.
JOHNNY