I've never lost any stone long term (never after the first few houres) inside. On durock, you may get a few that don't want to stay in the first few minutes, but after that, they should be fine. Also, I will never lay NTV without a bonding agent in the mortar. A few ounces per batch makes a huge difference in the mud, or you could use the thinset that NJ could recomend. The major difference between laying NTV & cultured, at least in my experiances, is you HAVE to lay NTV from the bottom up BED joints in place right away, meaning no going back later to grout.
I will admit that I've lost stone long term on the exterior of a house once though. It was cultured stone directly over a poured foundation wall at a partially exposed basement. About 25 stones fell over the winter, & 25 more were questionable when we went to replace the stone. We had laid the stone directly over the wall with no prep & my guys were having a hard time getting them stay in the first place. I should have known better in the first place, but I'd rather know what it takes to make the stone job fail on a small scale so I can have a better understanding what makes the stone job last long term. Very cheap lesson learned. On a side note, we did lose another 25 or so stones on this same house shortly after we set them originally. The drywallers had showed up late morning & had started hanging drywall on an exterior wall with nails. Unfortunately, this was a big house, & this hanger was FAST with his hammer! By the time someone got to him to tell him to stop pounding, the damage was done. Again not a big deal, but by this point, we were ready to get the job wrapped up & move on.
