Mike the Poolman


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Broken Pool Plaster, Calcium Nodules, Plaster Delamination, Pop-Offs

July 4, 2022

Plaster delamination is also known as a “Pop-Off”. A Pop-off is a section of plaster that has delaminated from its substrate creating a void between the plaster and gunite (or bond coat) and eventually breaks.

Pop-offs occur when cavities or voids form beneath a pool’s plaster surface, despite the best efforts of the plasterer. Although this process is not completely understood, 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.

Volcano-like bumps are a classic indicator of delamination. These “bumps” are referred to as Calcium Nodules. Calcium nodules are the first sign of delamination. The plaster beneath these calcium nodules is delaminating. Eventually, when someone steps on the hollow void or the pool cleaner runs over it, it “pops off” and leaves holes in the plaster with very sharp edges. .Many people describe them as looking like moon craters. I find that 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. when a pool is resurfaced,  I prefer the “chipping out” method which removes all existing plaster down to the gunite. 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!


Click here for a great article on Calcium Nodules from poolhelp.com

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