Maintaining a pool comes with a lot of responsibilities, one of which involves keeping an eye on little indicators that can tell you if something is wrong with the pool.

Often it might be difficult to notice the very small dips and cracks that build up to the larger problems. Among others, one of the ways you know something is wrong is when you notice calcium nodules in pools.

Yes, small, white calcium deposits in pools is a prime hint that there is some issue involved such as plaster delamination, crazing, or even severe structural cracks. Once you notice it, it’s best to call for help and get ready for some repairs before it adds up to more damage or higher repair costs.

Today, we will discuss all about “Calcium Nodules.” After reading this article, you will learn

• What calcium nodules are,
• How are they formed in pools
• How to temporarily get rid of calcium nodules,
• Actions to take once you notice them.

So let’s begin.

What Are Calcium Nodules?

In some pools, you will notice white or off-white bumps either in various spots on the pool floor, on the pool walls, or around any available cracks. These are calcium nodules in pools. If you try to touch them, you will find them to be rough, hard, and gritty.

Scientifically speaking, calcium nodules are small, rough deposits of Calcium Carbonate (CaCO₃) that can form on the surface of faulty plaster. They will only form when Calcium Hydroxide (Ca(OH)₂) from within the plaster comes in contact with pool water, maybe through pores, voids, or cracks, resulting in a reaction with Carbon dioxide (CO₂)and forming hardened Calcium Carbonate (CaCO₃) deposits.

Many will tell you that calcium nodules are caused by poor chemistry, i.e., due to aggressive Low-LSI water (or water undersaturated with Calcium Carbonate) and some will even try to tell them off as winter crystals.

But no. These are completely different. And while you can initially get rid of calcium nodules at a low cost, the more you wait to identify the root cause, the higher the chances your pool repair costs will be larger when you do it. (But yes, you should not straight out go for repair the first time you notice them unless you notice a visibly large crack. Be concerned when you see them forming too frequently after going through a removal process.)

Different Forms Of Calcium Nodules In Pools

Typically, you will find 3 forms of calcium nodules in pools:

• Floor Nodules
  These will appear round in shape and will form on horizontal surfaces.

• Wall Nodules
  You may notice calcium deposits dripping downwards from the pool wall, indicating cracks or crazing on the wall.

• Colored Nodules
  Pure calcium carbonate is white, meaning, most of the time, you will notice white calcium nodules. However, often nodules may absorb dirt, metals, or other contaminants, taking on different colors.
  For example:
  • Gray or Black – Often due to dirt, algae, or organic debris getting trapped in the nodule.
  • Brown – Caused by iron staining or organic material.
  • Green or Blue – Typically results from copper leaching from pool plumbing, heaters, or algaecides.
  • Yellow – This can be due to iron or organic staining.
  • Reddish or Rust-Colored – This usually indicates iron contamination from the pool water or corroding metal fixtures.

Now, let’s learn when calcium nodules may form.

Conditions That Lead To The Formation Of Calcium Nodules In Pools

Till now you have learned that calcium nodules are not formed due to chemical imbalance, but rather due to a chemical reaction between substances in the water and from within the plaster. In short, they form due to some underlying conditions in pools.

Let’s learn about these a bit more so that you know what you are dealing with when calcium nodules start to form in your pool.

1. Plaster Delamination (or Bond Failure)

Plaster delamination usually occurs due to poor plaster setup, to begin with.

Normally, you would want the plastering to be properly laid down with no gaps between the concrete and the plaster layer.

However, sometimes, while laying down the pool’s plaster layer, some separation may remain with its substrate (Gunite or Concrete). This may lead to the formation of small voids of air pockets.

Over time, water pressure creates tiny cracks or openings. This may let water enter these voids and dissolve the calcium hydroxide. And then this mixed solution may exit into the pool surface and react with the carbon dioxide there, forming Calcium Carbonate deposits, i.e., calcium nodules.

2. Crazing (or Surface Cracks)

Often, due to poor maintenance, pools will form cracks, better known as crazing, on the plaster due to excessive heat, wind exposure, or improper water curing.

Now, these cracks aren’t usually too large. But they are just enough to bring the pool water into contact with the calcium-rich components of the plaster, leading to nodule formation.

3. Structural Cracks

Structural cracks in swimming pools are definitely a concerning factor.

These are larger cracks that can go deep into the plaster or gunite, usually a result of poor construction practices, ground movement (like shifting soil from improper compaction), changes in groundwater levels, extreme weather conditions, improper design, or anything that may put too much stress on the pool’s concrete structure.

As you can tell, structural cracks give the pool water easy access to the plaster’s calcium hydroxide, leading to excessive calcium nodules in pools.

4. Improper Plastering Techniques

In some cases, you will find people going for amateur contractors to build their pools just to save some money on the construction costs. But what they don’t realize is, the construction is one of the most important steps when stepping up a pool.

You will need experts who understand proper mixing, can deliver the necessary water-to-cement ratios, and know the right proportion of chloride additives needed for plastering.

If done incorrectly, it may lead to shrinkage, forming cracks and voids, which, as you learned, results in nodule formation.

5. Replastering Issues

Similar to the previous point, this one is also dependent on the expertise of the people carrying it out.

You will hear about most pools experiencing calcium nodule formations right after replastering.

This is because when replastering, it’s quite difficult to achieve a strong bond between the old and new plaster. If not properly investigated early on, a weak bond can lead to delamination. And, as stated above, delamination is a prime cause of calcium nodules in pools.

What If You Have A Non-Plaster Surface?

The above reasons all indicate that calcium deposits in pools can only occur due to a plaster surface. But no, you can also expect to see calcium nodules in non-plaster surfaces.

• Tile Grout Nodules
  Nodules can form due to delamination in the grout/plaster/gunite interfaces. You will find cases where it may lead to a “volcano hole” where calcium continues to emerge.

• Fiberglass Nodules
  In case you have a fiberglass coating, you may still find nodules if there are pinholes in the coating. This will allow calcium from underlying plaster or gunite to seep through into the pool water.

So, just like plastered surfaces, you can also expect to find nodules of calcium deposits in pools with tiled surfaces or fiberglass coating.

How To Prevent Calcium Buildup In Pools

While calcium deposits in pools cannot always be completely prevented, you may follow these best practices to minimize their build-up.

I. Proper Plaster Application

It is important that you ensure the pool plaster is applied correctly with adequate curing time and minimal use of calcium chloride accelerators.

We always recommend you contact experts to carry it out and not amateurs. You want a pool that will last a long time, and not become a burden in the long run.

II. Bond Coating Before Replastering

Always go for higher quality. When replastering, make sure a high-quality bond coating is used to improve adhesion between layers and prevent delamination.

You want to ensure you get the utmost luxury with minimal maintenance cost.

III. Minimize Structural Movement

It’s best to build pools on stable ground to prevent excessive movement that can cause cracks.

IV. Regular Water Chemistry Maintenance

While poor water chemistry does not cause nodules, balanced water can help slow their growth.

Plus, poor water chemistry can lead to surface cracking which you certainly do not want.

How To Remove Calcium Nodules From Pools

Sure, you can prevent calcium nodules in pools. But what to do when they have already formed?

Here are a few methods that are commonly used.

1. Scraping or Sanding
   You may physically remove the nodules using a pumice stone or sanding block and smooth out the surface.

2. Acid Washing (With Caution)
   You may consider applying a diluted acid solution to dissolve calcium deposits. But be careful – excessive acid can damage plaster. It’s better to hire a professional who has done this before.

3. Drilling and Epoxying
   If you can identify the areas where the water reaches the Calcium Hydroxide, then you can consider drilling into the void and injecting epoxy. This will help seal the pathway and prevent water from carrying out more calcium hydroxide. Most professional pool builders with high experience will attempt this solution first before all else. But it’s not so quick or easy.

4. Plaster Repair or Resurfacing
   Despite the above efforts, if you notice that the calcium nodule formation shows no signs of stopping, then the final option is to replaster or resurface and stop the underlying delamination.

Avoid Misconceptions With Water Chemistry And Nodules – Know Your Facts

Now, you might ask how the misconceptions about “calcium nodule formation due to water chemistry” emerge.

Well, it’s just a misconception created by different amateur contractors to make people spend money on unnecessary solutions.

Here are the facts:

• Aggressive water prevents calcium nodule formation, while balanced water can actually make them more visible, but not influence their formation.

• High water hardness and pH can cause uniform calcium scaling, not form isolated nodules.

So, before you allow someone to implement a solution on your pool, make sure you have identified that what you are observing are in fact calcium nodules.

• First, understand that they are hardened and not soft or slimy.
• Try to rub some of the white substance and see if it is easy to rinse off the wall. If yes, it’s not a calcium nodule, but rather it could be just calcium scaling.
• If you do see a calcium nodule formation, then once getting rid of it, if it reappears on the same spot, then you can be sure there is delamination on that spot.
• Before attempting a DIY solution, make sure you are aware of the right condition and the problem. Consult with a professional if needed.

Final Thoughts

To conclude, calcium nodules are an indicator of plaster imperfections rather than a water chemistry issue. Now that you know their causes and the underlying structural problems they indicate, you can be ready to take action when you notice calcium nodules.

Having said that, we believe your pool is a mode of luxury that you want to be proud of. And if you properly maintain it, you are less likely to face any highly concerning issues.

But now that you know what calcium nodules in pools are and what causes their formation, make sure to be on the lookout. The first priority is always prevention. But if that doesn’t work, consider consulting with professional pool builders to help you identify the issue.

Remember, never go for amateur builders to handle what you love and enjoy. It may cost you a few extra bucks at times when hiring experienced professionals, but the output will be worth it. So if you are going to hire someone, hire professionals with proven track records to help you with your pool building and related solutions.

If you have any questions or experience to share, please do so in the comments below.

Cheers!