09/04/2026
What Are Those Little White โVolcanoesโ on Your Pool Surface?
Theyโre called "calcium nodules", and they are often misunderstood.
Unlike normal calcium scale that forms on top of the pool surface because of water chemistry, calcium nodules usually begin **behind the plaster**.
Small cracks, pinholes, hollow areas, or separation between the plaster and the pool shell can allow pool water to get underneath the finish. Once water reaches that area, it creates a calcium-rich environment behind the plaster.
That calcium-rich water slowly finds its way back through the tiny crack or pinhole. When it reaches the pool water, a chemical reaction occurs and **calcium carbonate begins to build up around that opening**.
Over time, it creates those small, hard, white spots that sometimes look like tiny **volcanoes** growing out of the pool surface.
Important: Calcium nodules are not automatically a sign of poor weekly pool service or bad chemical maintenance.
In many cases, the underlying cause is related to the pool surface itself โ such as:
โข Poor bonding between plaster and the pool shell
โข Delamination or hollow areas behind the plaster
โข Hairline cracks or pinholes
โข Improper plaster preparation or application
โข Movement or aging of the pool structure
Sometimes these problems don't appear until **many years after the pool was built or resurfaced.
Maintaining properly balanced water is extremely important for protecting your pool, but when true calcium nodules appear, simply adjusting the chemicals usually won't fix the underlying problem.
Understanding where the calcium is coming from is the first step toward determining the correct repair.