Oh, just spotted flagstone coping. Tough one. I loooove the look of my flagstone, but it's been a challenge. Flagstone is basically compressed sand. It can flake and/or releases sand. Mine does both. Putting your feet or hands or butt in a puddle of sand while getting in and out is not all that fun. And the cleaner has to deal with it, of course, 'cause it gets into the pool. I believe there are quarries that produce flagstone without these issues, but mine is not from one of those! I had to treat the stone with a veeeerrrry expensive sealer (like $3K for a small pool, regular stone/paver sealer does nothing), that all but eliminated the sand problem. But it still flakes some. So if yours does what mine does, there is a semi-solution. Short of that, I don't know how to steer you to "the good stuff." Perhaps your PB knows of this, or others here know what to do about this potential problem.
Also, the way my stone was installed was with a very rough, organic edge to it. Looks great, but it's like broken stone (it is broken stone). I keep thinking one of the kids is going to bang into that, or scrape against it somehow and end up with a much worse wound than a smooth edge would have caused (though in five years that hasn't happened, so it could be a worry for nothing). Something to think about and talk with your designer about.
It's not comfortable to lean against, like from a bench or your shelf. Is this what you're getting:
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