I am replacing one 12" floor tile. How much premium two part mortar and part A polymer should I use and how do I mix it

Billy, Click on and read the links provided to learn how to tile a floor.
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http://novafloor.us/installation-guides
http://novafloor.us/wp-content/uploads/2014/09/Installation-Guidelines-for-Direct-Glue-Tile_Grout-v2-10_2015.pdf
http://novalis-intl.us/wp-content/uploads/2012/10/LUXURY-VINYL-TILE-INSTALLATION-GUIDE.pdf

who ever installed it probably didn't use a tile underlay like wonderboard or hardibacker. Also for areas like that you have to get the good thinset mortar like FLEXbond and the other thing too is Saltillo is not very user friendly when it comes to installing if you're not fast because its so porous i literally sucks the moisture from the mortar and there for doesnt bond to ur surface. If the thinset is thick and dry it aint gonna work. ALSO WITH SALTILLO YOU MUST HAVE 100% COVERAGE WITH THE THINSET.. Hollow tiles or no thinset under corners and what not just going to pop up. I butter the floor AND the back side of the tile when doing that type of tile. It's not very flat so there for you must have alot of thinset mortar under each and every tile. good luck. hope this helped. I been doing custom tile for 25 years so i got ya on this. Who ever was the installer lacked some knowledge on Saltillo. Tear it up and get something nicer.

Your not troweling enough glass thinset onto the wall. The thinset should be creamy and troweled evenly most people hold the trowel to flat or use to small of a trowel you also could lightly coat the back do the tile to give it a good mechanical bond

you cannot, only way is to replace crack tile. any "hairline restorer" "hairline paint" are simple cons and do not work! crack meant that these two bits move differently and need to be replaced with single unit, matter will go only worse.

I would try breaking the tile up with hammer instead of prying from side, as you maybe chip or crack adjoining tiles. This method should work fine, you may loosen surrounding tiles but just re-mortar any tiles that may become loose. Wear eye protection. Good luck

Mortar, go to a tile supply store and ask for the best tile mortar for granite.

Glue is fast and easy but pails in performance to that of mortar.