Calcium nodules are the first sign of delamination.
Calcium nodules (see photos below) are bumps that look like bird droppings or boogers on the plaster. They are most noticeable in colored pools because the calcium nodules are always white or slightly tan. As calcium nodules mature they create a hollow space beneath the pool’s plaster surface.
Although this process is not completely understood, these “hollows” or voids can be caused by a number of things, including plaster shrinkage, cracks, bad bond coats, and hollow spots between pool fixtures and the plaster. When the void fills with water, a process is set in motion as the water mixes with calcium hydroxide in the plaster. This results in volcano-like bumps or mounds on the floors and walls of your pool. As times passes the mounds increase in size and height. When someone steps on it or the pool cleaner runs over it enough times its “pops” and a creates a section or hole of broken plaster with very sharp edges known as a Pop Off. A Pop Off looks very much like a moon crater.
Most pop offs occur in replastered pools.
Most of these pools are plaster over plaster. If the plaster company has not prepared the pool properly before replaster, pop offs are more likely! For this reason I prefer “chipping out” all existing plaster down to the gunite before resurfacing. There are companies in our area that will chip out and there are companies that will not. If you are replastering, be sure and ask me!
You do not need to drain your pool to repair a Pop Off.
Pop offs can be reapired without draining your pool. I will cut out pop offs down to the gunite and patch to closely match your existing plaster. All work is done underwater without draining your pool.
Make sure and check my blog for articles & recent photos on Pop Offs & Calcium Nodules.
Swimming Pool photos of Calcium Nodules and Broken Plaster aka Pop Offs:
Finally, this is an EXCELLENT article on pop-offs and plaster delamination including illustrations: