Why Are Calcium Crystals Forming in Pools?

[onBalance]

In recent years, calcium crystals have been forming during the winter at a higher rate in some newly plastered swimming pools. From the reports we have heard, this problem seems to occur more often in the northeast of the country. Apparently, pool builders, plasterers, and service techs involved have not been able to determine the cause of these sharp and abrasive crystals and how to prevent them from forming on new plaster surfaces, including quartz and pebble.

(It should be noted that calcium crystals are different in appearance and form than the typical calcium scale that develops due to high pH and/or hard water), or calcium nodules that develop due to plaster delamination (bond failure) and in cracks.

Some think that the root cause of calcium crystal formation is aggressive water. More specifically, the theory is that some pools are not being properly winterized and adjusted for the soon-to-be lower and cold-water temperatures that can make water aggressive (See LSI). Also, that calcium from the plaster is being dissolved by aggressive water and then somehow that causes calcium crystals to start growing on the plaster surface.

That raises some questions. If aggressive water is dissolving calcium carbonate, how does it also form and grow calcium carbonate crystals at the same time? Has the plaster surface been analyzed for LSI aggressive water attack for confirmation? Why don’t all plaster pools with aggressive water develop crystals? Of course, aggressive water doesn't add up as a credible cause.

Let’s explore some other possibilities for this crystal phenomenon.

Plaster Issues

What is not widely known in our industry is that when plaster workmanship is poor, two forms of soluble calcium can dissolve out of new plaster, without the water even being aggressive. Yes, in water that is perfectly balanced. Those plaster components are calcium hydroxide, and calcium chloride. When those two compounds “bleed” into the pool water, that increases the pH, alkalinity, and calcium level. Those increases should not automatically be assumed to have been caused by LSI aggressive water. It may be due to poorly made plaster.

It is worthy to note that the concrete and cement industry (ACI and PCA) acknowledges that cement quality, or lack thereof, plays a huge role in the amount of efflorescence and/or dusting (among other problems and defects) that develops on new concrete finishes. They have identified high water content while mixing, high calcium chloride content, and poor troweling techniques (excessive water troweling) as reasons leading to a weak, porous, and micro-cracking cement finish. Those are issues that enable efflorescence (calcium) to form on cement surfaces. Is pool plaster much different?

Are some plasterers adding extra calcium chloride to plaster mixes during colder temperatures to speed up the plastering process, so that it doesn’t take all day? Does this lead to calcium hydroxide and calcium chloride dissolving out of plaster regardless of the water balance, thereby increasing the pH, alkalinity, and calcium levels? Could this be a recipe for calcium crystals to develop? Yes.

Chemical Start-up Issues

Differences in startup chemistry processes can have a significant impact on new plaster surfaces. For twenty-five years, onBalance’s Bicarb startup (Positive LSI startup) has shown to help prevent “plaster dust” from forming in new plaster pools. Would that startup program help negate crystal formation over the winter?

The NPC’s Traditional startup does NOT prevent plaster dust in newly plastered pools. In fact, it enables it. A lot of plaster dust means that the plaster surface has lost material and becomes more porous which can lead to more soluble plaster material being easily dissolved out. Does this startup program contribute to the crystal formation problem?

We all know that improper water chemistry can lead to various problems. But it is obvious that there are other issues (and the plaster itself) that need to be investigated and analyzed to determine the cause(s) and prevention of wintertime crystals.

 

[JoyfulNoise]

Thank Kim! Great write up.

I have always been very against gunite/plaster builds in the northeast. If I ever lived back East, I would never build a gunite pool. Even if you managed to be the first on a builders schedule and you got started in the cold/wet spring, you’d barely get the pool finished by summer and then you would have a brand new plaster pool closing in the first winter. Given how difficult it is to maintain pH with a newly plastered pool, and no ability to add or monitor chemicals over the winter, it’s just too risky.

I would also investigate chemicals used. Sulfates (dry acid and MPS) are pushed by a lot of pool stores and professional techs. Calcium sulfate (gypsum) scale can form at ANY pH and once it starts growing it won’t stop. It’s a scaling process that is initiated and controlled by the presence of nucleation sites and there’s plenty of surface roughness in a plaster pool to start it off.

Do pool plaster compositions use any gypsum in them?

 

[ajw22]

For reference purposes, to see the differing views in the industry below is Ordenda Techologies explanation for calcium crystals...

Calcium Crystals vs. Scale

Calcium crystals grow out of plaster surfaces in pools during the winter. Most are calcite, but there are many forms. Learn how to prevent crystals in your pool.

blog.orendatech.com

 

[JamesW]

The lack of circulation probably allows a thin layer of high CSI water to form near the plaster surfaces and create scale crystals.

Possibly high pH and high calcium from the calcium hydroxide near the surface.

I would try to circulate the water to prevent any local high CSI conditions.

Brushing would also be a good idea.

Maybe, periodically pull back the cover and brush and balance.

 

[JamesW]

Orenda calls these two examples scale from high LSI pool water, but they are efflorescence, which has nothing to do with pool water chemistry.

Calcium Crystals vs. Scale

Calcium crystals grow out of plaster surfaces in pools during the winter. Most are calcite, but there are many forms. Learn how to prevent crystals in your pool.

blog.orendatech.com

 

[onBalance]

James, I agree with you that a lack of circulation (water movement) and brushing during the wintertime would aid in calcium crystals forming on poor quality pool plaster. This issue is somewhat similar to plaster dust forming in newly plastered pools. If no brushing occurs, then plaster dust and crystals can easily hardened onto the plaster surface.

As for Orenda's blogs on calcium scale, the different and various forms of calcium carbonate scale is complicated. And as I see it, some of their explanations for a couple of calcium scale formations are incorrect.

Matt, that is a good point about the issue of sulfates and the problems it creates. Also, it is my understanding that Portland Cement (which both concrete and pool plaster significantly contains) has a small amount of gypsum added to control the speed of hardening.

 

[JoyfulNoise]

Brushing would be a great idea … except when there is 3ft of snow on the ground with 4-1/2ft drifts and the location of the pool cover is anyone’s guess …

 

[onBalance]

Or a solid foot of ice under that pool cover. No getting underneath that with an aluminum pole.

 

[Poolspoolspools]

I have been working in the pool service industry in NJ for seven seasons now and these crystals have been the bane of my existence the entire time. With that said I actually owe a lot to them because they are really what had initially made me want to get more educated so that I could provide the best service possible because I thought it was my fault. I have read every piece of material I could get my hands on, all the NESPA books, countless forum posts, every orenda blog post as well as getting my NPC start up certification and I feel like I still know the same about them now as I did a few years ago. Infact I only found the post because of my yearly search to see if there was more info available.

I have followed orendas advice for 3 seasons and it is my opinion now that their prevention method does not work. I agree that this is a localzied lsi violation though. I have seen pools that were started up with methods that I didn't agree with form crystals and also not form crystals. I have seen pools started up in NPC fashion as well as onBalance form crystals and not form crystals. I have reviewed coworkers incorrect seasonal chemistry and the best balanced pools form crystals. Polished pools forming crystals the next season with monthy winter watch and chemistry adjustments.

It's always the same pools forming crystals though and they are growing by the seasons. I think I'm finally at the point where I can point the fingers to workmanship or maybe I'm just tired from all the brushing. . . It's probably my fault. . .see you next year

 

[onBalance]

Thank you for your perspective and experience. It is not an LSI violation.
Faulty workmanship and materials (additives) plays the biggest role with this plaster problem.
What is needed is to stop assuming it is a water chemistry mistake and for builders to take plaster samples from these problem pools and have them analyzed for defects.
I am willing to work with you in documenting the cause for this problem. Contact me with a PM.

 

[JamesW]

I think that if the water is not moving at all, the CSI within a few millimeters of the surface can be much higher than in the rest of the pool.

I would try to find a way to get some circulation in the pools and periodically check the chemistry to see how it is changing.

 

[onBalance]

The CSI can be much higher within a few millimeters of the plaster surface ONLY if the plaster surface itself is weak and porous and releasing SOLUBLE calcium hydroxide from within a defective surface and causing the CSI to rise.

Balanced water would not cause a high CSI next to the surface because all good plaster finishes (including quartz and pebble) result with a "calcium carbonate" plaster surface which doesn't dissolves in balanced water.

Aggressive CSI water does and would dissolve calcium carbonate until the CSI is balanced (0.0) but then would stop dissolving calcium carbonate and raising the CSI any higher.

Circulation and brushing can help to prevent calcium crystals developing on a plaster surface that is weak and porous and releasing soluble calcium hydroxide.

Let's be clear that this problem is not about aggressive water or the lack of water circulation and brushing because quality plaster that was applied correctly and the workmanship and material was good does not typically develop this problem.

 

[JamesW]

Let's be clear that this problem is not about aggressive water or the lack of water circulation and brushing because quality plaster that was applied correctly and the workmanship and material was good does not typically develop this problem.

Even if we accept that the main cause is related to defective plaster application or materials, the lack of circulation and brushing is still a valid point.

Without knowing beforehand which pools will, or will not, develop crystals, the best practice would be to find a way to create some circulation and brush if possible and make sure that the pH does not go sky high.

 

[JamesW]

In any case, you’re still trying to prevent the formation of the crystals.

Once the plaster is applied, you can’t do anything about the plaster if it is defective other than remove the bad plaster and replace it.

If you’re not going to replaster, you still want to prevent the formation of crystals, which will probably require some sort of circulation, chemistry management and brushing if possible.

You can do nothing and allow the crystals to form and then go to the plaster company and say “See, the formation of crystals proves that the plaster is defective and you need to replaster under warranty”.

However, it’s unlikely that the plaster company would agree and then you still have to deal with removing the crystals.

If you’re a service person who closed the pool, the homeowner will ask you why the crystals formed and you might blame the plaster company and the plaster company will say that it’s a chemistry issue and blame you.

So, the homeowner does not know who to believe because all they see is two professionals pointing fingers at each other.

 

[onBalance]

I agree that we want to prevent the formation of crystals. And yes, brushing and water circulation may help to prevent crystals. We are on the same page with that issue, and I have stated that twice previously. However, brushing the pool, trying to create water circulation during the winter isn’t always possible. And that is simply a Band-Aid approach.

Even if crystals can be prevented by brushing during the winter, that doesn’t resolve or address the fact that the plaster quality is likely to be very poor (in a particular defective pool) and that the plaster finish isn’t likely to last 20+ years as it would if plastered with proper workmanship.

The best and right way to prevent crystals is to use quality workmanship and materials when plastering. That is the reason I wrote this article and posted it. I am trying to get this information out to everyone that is, or will be, involved with new plaster pools.

Should we just allow some plasterers (who do bad workmanship) to get away with poor workmanship and not take responsibility? Should we not confront them? I believe that good plasterers don’t like the bad plasterers under-bidding them by rushing through a plaster job with poor workmanship and then getting away with it. Allowing that doesn't help them compete and make a profit.

If enough good builders, plasterers, service techs, and knowledgeable pool owners understand the true cause for calcium crystals to develop and confront the bad plasterers and demand replastering of defective plaster jobs, we might start making some progress with this issue.

 

[JamesW]

Should we just allow some plasterers (who do bad workmanship) to get away with poor workmanship and not take responsibility? Should we not confront them?

Yes, we want to hold the plasterers accountable.

Ideally, all plaster would be done perfectly every time, but in the real world, service people still have to deal with imperfect products.

Even if we agree that crystals are due to quality control issues related to application or materials, the industry and trade groups will still debate and deny.

Until the industry agrees or you come up with some sort of widely accepted definitive test that proves that the plaster is defective, all the customer sees is a debate between the service person and the plaster trade companies and plaster industry groups.

If the customer gets crystals and determines that the plaster quality is at fault, they can ask the plasterer to redo it under warranty, but what if the plasterer denies responsibility?

When a property owner sees the scale and asks the service tech why it happens and the tech blames the plaster company, how does the property owner know that the service person is actually correct and not just some incompetent person trying to blame everyone else for problems they created?

What proof is available that a homeowner can refer to that definitely proves that the crystals are due to bad workmanship or bad materials?

 

[JamesW]

If a homeowner gets crystals, they can ask the plaster company to redo it under warranty and a few might, but most probably won’t.

The only way to force the company to replaster for free is to file a civil suit.

To win, you would need to get an industry professional expert who can testify that the crystals are due to poor quality materials or workmanship.

The professional would also need to provide a lab report from a certified lab that specifies what the defect was or you need a reference that says that crystals that grow during the winter can only be due to poor quality materials and workmanship.

What lab will do such analysis?

What accepted trade reference says that the crystals that grow during the winter can only be due to poor quality materials and workmanship?

The plaintiff bears the burden of proof by a preponderance of evidence.

 

[onBalance]

As is mentioned in my original post above, both the PCA and ACI state that adding a high amount of calcium chloride, a high amount of water, and wet troweling is known to cause shrinkage and porosity of cement surfaces, which then can result in efflorescence forming on various cement products.

You asked, "What lab will do such analysis."

There are many certified cement labs that will analyze cement products for its' calcium chloride content, water content, and a weak porous surface. I assure you that an analysis of new plaster of pools that end up with a severe crystal problem will have a high calcium chloride content. That is evidence.

Anyone claiming that "aggressive water" causes the formation of calcium carbonate crystals need to explain how crystals can form (a scaling situation) in or by aggressive water. And why don't older pools typically result with crystals as do some recently plastered pools? "What trade group reference says that crystals can only grow in aggressive water? Let's demand those answers."

What is needed in our industry are people who will stand up, speak up, and encourage others to consider having the plaster analyzed instead of simply giving up and suggesting that the service tech or pool owner should have run the filter pump and brushed the pool during the winter. That alone gives protection to the bad plastering companies.

 

[JoyfulNoise]

You both are making excellent points and I feel that you’re a lot closer on the issue than further apart. But I think before anyone can really make a definitive claim, the “crystals” need to be chemically analyzed. One of the assumptions here is that these crystals are calcium carbonate. That may be true or it may not be. “Scaling” or precipitation of calcium and magnesium bearing compounds is quite complex. While calcium carbonate precipitation is dependent on pH, neither calcium sulfate nor calcium phosphate scale is. Those precipitates are driven mainly by concentration and nucleation at a suitable location. These crystals could be a mixed precipitate as well - calcium and magnesium carbonates, sulfates and phosphates. The scale that forms on my tile surfaces is somewhat reactive to acid but not all it dissolves even in concentrated MA. So I knew there’s much more to the scale that I see on my pool than simply being CaCO3. This is very likely a multifaceted problem that involves both complex water chemistry and surface chemistry issues.

Unfortunately swimming pools are luxury items and not at all considered to be critically important in nature. Unlike a medical procedure or a bridge, no one will die from their plaster looking ugly. The kinds of rigorous scientific and engineering studies that go into making safe medicines or building a structure that can withstand an earthquake are not going to be undertaken by an industry that builds luxury personal items. You might be out $10k from a lousy plaster contractor but few people will shed a tear over that. But that shouldn’t stop the people here from investigating and looking for better answers so that all pool owners can benefit from these inquiries and make better choices to safeguard their investment.

I still boil it down to this simple conclusion - people who live in the Northeast are nuts for building plaster pools. Vinyl is a much more appropriate choice for the climate and environment there. Leave the plaster for us desert rats to deal with and you all have fun with your giant plastic bag full of water …

 

[onBalance]

Thanks Matt. I have been able to have crystals from several pools analyzed. They were comprised of calcium carbonate.