We had two small (6") bubbles form on our shallow end after a year or so. Just this weekend, they broke up and I now need to patch them. The fractured pieces, however, reveal that the ultraguard is still bound to the pool surface, and it was the underlying material that broke up, forming the bubble. Yet another piece of evidence that you need to grind the &^%$# out of the surface and make sure it is solid before you start.