What does the manufacturer suggest?

I could not find any recommendations on their websiteI . I might have seen something like refer to some masonry standards. I did try to go through some of those. I have read some general stone instructions you need grout outside but we have used (as so many others have) individual stacked stones on a walls/pillars in our front yard that have been fine for 15 years or so. I did not get a response from the question sent through their website. I can try again but I thought someone might know the answer here.