How To Remove Calcium Nodules From A Pool

Calcium nodules are a form of efflorescence, which means that water is coming from behind the plaster or tile and bringing calcium with it, which then forms onto the outside of the tile or plaster surface through hairline cracks. This is a similar formation as what you would see inside of a cave in the form of a stalactite or stalagmite. Sometimes there is a small pocket of water behind the plaster in between the Gunite and the plaster. Other times water is actually seeping through the 8 inches of Gunite and through hairline cracks of the plaster to form calcium nodules in the pool. If there's only a small pocket of water and you remove the calcium nodule, and the water neutralizes with the water that's in the pool, you will not form a new calcium nodule, once the old one is removed. If the water is seeping from behind the pool through the Gunite and into the pool, the calcium nodule will form again and again.

Removal of the calcium nodule can be done with a diamond sanding pad as long as you are careful not to scratch the plaster surface. You may need to do this once per year until you decide to resurface the pool. Make sure if you are going to resurface the pool that the company that you hire knows that you are having problems with calcium nodules and they take extra precautions to create a better bond coat or water tight seal before they resurface the pool. This will prevent your new pool surface from forming these nodules. 

The other reason why I have seen these nodules on certain pools is because the plaster company did not fully remove the old plaster before they shot on their new plaster. They simply scratched the surface or lightly sandblasted to try to create a rough enough surface for the new plaster to bond to, and that is not usually enough.