I have coping around the exterior of my pool, with about 6 inches of tile below the coping. Each year, some of the tiles fall off. Each year. I've replaced the tile using a mortar supposedly appropriate for wet (in water) applications. The tiles generally do not stay in place for more than a season, maybe some for two. It's gotten progressively worse.
Last year, I got a recommendation for a pool repair guy who specializes specifically in these problems. He came over and tapped the coping with a rock. Some sections sounded hollow, others did not. He told me that the hollow sound meant that the coping had separated and that it needed to be replaced. He said that he could replace some or all of the coping (all at a cost of ~$5,000), which he'd fabricate to match the existing style. While it might be less money to replace only some of the stones, he might or might not have sufficient tile in my pattern to make repair feasible. Even if he does, I'm starting to thing that the scope of my problem will make full replacement the best option.
Does anyone have experience with this? Does this sound reasonable? Are there other, better solutions? And what might cause this problem (and, therefore, might be done differently to prevent it from recurring)?