I have edited this post because I am doing what I always do when I don't know something....find someone who does!
I have put in a call to Granicrete, to determine the chemical make up of said product. I will call tile store where we purchase excellent setting materials....and owner will email Kiesel...to determine chemical compatibility.
Then if it is not recommended...I will inform the homeowner and let them know we must start from scratch. We are pretty good at that, unfortunately....since so many people do showers incorrectly.